/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include "resolv_cache.h"
#include <resolv.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include "pthread.h"
#include <errno.h>
#include <arpa/nameser.h>
#include <sys/system_properties.h>
#include <net/if.h>
#include <netdb.h>
#include <linux/if.h>
#include <arpa/inet.h>
#include "resolv_private.h"
#include "resolv_netid.h"
#include "res_private.h"
#include "private/libc_logging.h"
/* This code implements a small and *simple* DNS resolver cache.
*
* It is only used to cache DNS answers for a time defined by the smallest TTL
* among the answer records in order to reduce DNS traffic. It is not supposed
* to be a full DNS cache, since we plan to implement that in the future in a
* dedicated process running on the system.
*
* Note that its design is kept simple very intentionally, i.e.:
*
* - it takes raw DNS query packet data as input, and returns raw DNS
* answer packet data as output
*
* (this means that two similar queries that encode the DNS name
* differently will be treated distinctly).
*
* the smallest TTL value among the answer records are used as the time
* to keep an answer in the cache.
*
* this is bad, but we absolutely want to avoid parsing the answer packets
* (and should be solved by the later full DNS cache process).
*
* - the implementation is just a (query-data) => (answer-data) hash table
* with a trivial least-recently-used expiration policy.
*
* Doing this keeps the code simple and avoids to deal with a lot of things
* that a full DNS cache is expected to do.
*
* The API is also very simple:
*
* - the client calls _resolv_cache_get() to obtain a handle to the cache.
* this will initialize the cache on first usage. the result can be NULL
* if the cache is disabled.
*
* - the client calls _resolv_cache_lookup() before performing a query
*
* if the function returns RESOLV_CACHE_FOUND, a copy of the answer data
* has been copied into the client-provided answer buffer.
*
* if the function returns RESOLV_CACHE_NOTFOUND, the client should perform
* a request normally, *then* call _resolv_cache_add() to add the received
* answer to the cache.
*
* if the function returns RESOLV_CACHE_UNSUPPORTED, the client should
* perform a request normally, and *not* call _resolv_cache_add()
*
* note that RESOLV_CACHE_UNSUPPORTED is also returned if the answer buffer
* is too short to accomodate the cached result.
*/
/* the name of an environment variable that will be checked the first time
* this code is called if its value is "0", then the resolver cache is
* disabled.
*/
#define CONFIG_ENV "BIONIC_DNSCACHE"
/* default number of entries kept in the cache. This value has been
* determined by browsing through various sites and counting the number
* of corresponding requests. Keep in mind that our framework is currently
* performing two requests per name lookup (one for IPv4, the other for IPv6)
*
* www.google.com 4
* www.ysearch.com 6
* www.amazon.com 8
* www.nytimes.com 22
* www.espn.com 28
* www.msn.com 28
* www.lemonde.fr 35
*
* (determined in 2009-2-17 from Paris, France, results may vary depending
* on location)
*
* most high-level websites use lots of media/ad servers with different names
* but these are generally reused when browsing through the site.
*
* As such, a value of 64 should be relatively comfortable at the moment.
*
* ******************************************
* * NOTE - this has changed.
* * 1) we've added IPv6 support so each dns query results in 2 responses
* * 2) we've made this a system-wide cache, so the cost is less (it's not
* * duplicated in each process) and the need is greater (more processes
* * making different requests).
* * Upping by 2x for IPv6
* * Upping by another 5x for the centralized nature
* *****************************************
*/
#define CONFIG_MAX_ENTRIES 64 * 2 * 5
/* name of the system property that can be used to set the cache size */
/****************************************************************************/
/****************************************************************************/
/***** *****/
/***** *****/
/***** *****/
/****************************************************************************/
/****************************************************************************/
/* set to 1 to debug cache operations */
#define DEBUG 0
/* set to 1 to debug query data */
#define DEBUG_DATA 0
#if DEBUG
#define __DEBUG__
#else
#define __DEBUG__ __attribute__((unused))
#endif
#undef XLOG
#define XLOG(...) ({ \
if (DEBUG) { \
__libc_format_log(ANDROID_LOG_DEBUG,"libc",__VA_ARGS__); \
} else { \
((void)0); \
} \
})
/** BOUNDED BUFFER FORMATTING
**/
/* technical note:
*
* the following debugging routines are used to append data to a bounded
* buffer they take two parameters that are:
*
* - p : a pointer to the current cursor position in the buffer
* this value is initially set to the buffer's address.
*
* - end : the address of the buffer's limit, i.e. of the first byte
* after the buffer. this address should never be touched.
*
* IMPORTANT: it is assumed that end > buffer_address, i.e.
* that the buffer is at least one byte.
*
* the _bprint_() functions return the new value of 'p' after the data
* has been appended, and also ensure the following:
*
* - the returned value will never be strictly greater than 'end'
*
* - a return value equal to 'end' means that truncation occured
* (in which case, end[-1] will be set to 0)
*
* - after returning from a _bprint_() function, the content of the buffer
* is always 0-terminated, even in the event of truncation.
*
* these conventions allow you to call _bprint_ functions multiple times and
* only check for truncation at the end of the sequence, as in:
*
* char buff[1000], *p = buff, *end = p + sizeof(buff);
*
* p = _bprint_c(p, end, '"');
* p = _bprint_s(p, end, my_string);
* p = _bprint_c(p, end, '"');
*
* if (p >= end) {
* // buffer was too small
* }
*
* printf( "%s", buff );
*/
/* add a char to a bounded buffer */
char*
_bprint_c( char* p, char* end, int c )
{
if (p < end) {
if (p+1 == end)
*p++ = 0;
else {
*p++ = (char) c;
*p = 0;
}
}
return p;
}
/* add a sequence of bytes to a bounded buffer */
char*
_bprint_b( char* p, char* end, const char* buf, int len )
{
int avail = end - p;
if (avail <= 0 || len <= 0)
return p;
if (avail > len)
avail = len;
memcpy( p, buf, avail );
p += avail;
if (p < end)
p[0] = 0;
else
end[-1] = 0;
return p;
}
/* add a string to a bounded buffer */
char*
_bprint_s( char* p, char* end, const char* str )
{
return _bprint_b(p, end, str, strlen(str));
}
/* add a formatted string to a bounded buffer */
char* _bprint( char* p, char* end, const char* format, ... ) __DEBUG__;
char* _bprint( char* p, char* end, const char* format, ... )
{
int avail, n;
va_list args;
avail = end - p;
if (avail <= 0)
return p;
va_start(args, format);
n = vsnprintf( p, avail, format, args);
va_end(args);
/* certain C libraries return -1 in case of truncation */
if (n < 0 || n > avail)
n = avail;
p += n;
/* certain C libraries do not zero-terminate in case of truncation */
if (p == end)
p[-1] = 0;
return p;
}
/* add a hex value to a bounded buffer, up to 8 digits */
char*
_bprint_hex( char* p, char* end, unsigned value, int numDigits )
{
char text[sizeof(unsigned)*2];
int nn = 0;
while (numDigits-- > 0) {
text[nn++] = "0123456789abcdef"[(value >> (numDigits*4)) & 15];
}
return _bprint_b(p, end, text, nn);
}
/* add the hexadecimal dump of some memory area to a bounded buffer */
char*
_bprint_hexdump( char* p, char* end, const uint8_t* data, int datalen )
{
int lineSize = 16;
while (datalen > 0) {
int avail = datalen;
int nn;
if (avail > lineSize)
avail = lineSize;
for (nn = 0; nn < avail; nn++) {
if (nn > 0)
p = _bprint_c(p, end, ' ');
p = _bprint_hex(p, end, data[nn], 2);
}
for ( ; nn < lineSize; nn++ ) {
p = _bprint_s(p, end, " ");
}
p = _bprint_s(p, end, " ");
for (nn = 0; nn < avail; nn++) {
int c = data[nn];
if (c < 32 || c > 127)
c = '.';
p = _bprint_c(p, end, c);
}
p = _bprint_c(p, end, '\n');
data += avail;
datalen -= avail;
}
return p;
}
/* dump the content of a query of packet to the log */
void XLOG_BYTES( const void* base, int len ) __DEBUG__;
void XLOG_BYTES( const void* base, int len )
{
if (DEBUG_DATA) {
char buff[1024];
char* p = buff, *end = p + sizeof(buff);
p = _bprint_hexdump(p, end, base, len);
XLOG("%s",buff);
}
} __DEBUG__
static time_t
_time_now( void )
{
struct timeval tv;
gettimeofday( &tv, NULL );
return tv.tv_sec;
}
/* reminder: the general format of a DNS packet is the following:
*
* HEADER (12 bytes)
* QUESTION (variable)
* ANSWER (variable)
* AUTHORITY (variable)
* ADDITIONNAL (variable)
*
* the HEADER is made of:
*
* ID : 16 : 16-bit unique query identification field
*
* QR : 1 : set to 0 for queries, and 1 for responses
* Opcode : 4 : set to 0 for queries
* AA : 1 : set to 0 for queries
* TC : 1 : truncation flag, will be set to 0 in queries
* RD : 1 : recursion desired
*
* RA : 1 : recursion available (0 in queries)
* Z : 3 : three reserved zero bits
* RCODE : 4 : response code (always 0=NOERROR in queries)
*
* QDCount: 16 : question count
* ANCount: 16 : Answer count (0 in queries)
* NSCount: 16: Authority Record count (0 in queries)
* ARCount: 16: Additionnal Record count (0 in queries)
*
* the QUESTION is made of QDCount Question Record (QRs)
* the ANSWER is made of ANCount RRs
* the AUTHORITY is made of NSCount RRs
* the ADDITIONNAL is made of ARCount RRs
*
* Each Question Record (QR) is made of:
*
* QNAME : variable : Query DNS NAME
* TYPE : 16 : type of query (A=1, PTR=12, MX=15, AAAA=28, ALL=255)
* CLASS : 16 : class of query (IN=1)
*
* Each Resource Record (RR) is made of:
*
* NAME : variable : DNS NAME
* TYPE : 16 : type of query (A=1, PTR=12, MX=15, AAAA=28, ALL=255)
* CLASS : 16 : class of query (IN=1)
* TTL : 32 : seconds to cache this RR (0=none)
* RDLENGTH: 16 : size of RDDATA in bytes
* RDDATA : variable : RR data (depends on TYPE)
*
* Each QNAME contains a domain name encoded as a sequence of 'labels'
* terminated by a zero. Each label has the following format:
*
* LEN : 8 : lenght of label (MUST be < 64)
* NAME : 8*LEN : label length (must exclude dots)
*
* A value of 0 in the encoding is interpreted as the 'root' domain and
* terminates the encoding. So 'www.android.com' will be encoded as:
*
* <3>www<7>android<3>com<0>
*
* Where <n> represents the byte with value 'n'
*
* Each NAME reflects the QNAME of the question, but has a slightly more
* complex encoding in order to provide message compression. This is achieved
* by using a 2-byte pointer, with format:
*
* TYPE : 2 : 0b11 to indicate a pointer, 0b01 and 0b10 are reserved
* OFFSET : 14 : offset to another part of the DNS packet
*
* The offset is relative to the start of the DNS packet and must point
* A pointer terminates the encoding.
*
* The NAME can be encoded in one of the following formats:
*
* - a sequence of simple labels terminated by 0 (like QNAMEs)
* - a single pointer
* - a sequence of simple labels terminated by a pointer
*
* A pointer shall always point to either a pointer of a sequence of
* labels (which can themselves be terminated by either a 0 or a pointer)
*
* The expanded length of a given domain name should not exceed 255 bytes.
*
* NOTE: we don't parse the answer packets, so don't need to deal with NAME
* records, only QNAMEs.
*/
#define DNS_HEADER_SIZE 12
#define DNS_TYPE_A "\00\01" /* big-endian decimal 1 */
#define DNS_TYPE_PTR "\00\014" /* big-endian decimal 12 */
#define DNS_TYPE_MX "\00\017" /* big-endian decimal 15 */
#define DNS_TYPE_AAAA "\00\034" /* big-endian decimal 28 */
#define DNS_TYPE_ALL "\00\0377" /* big-endian decimal 255 */
#define DNS_CLASS_IN "\00\01" /* big-endian decimal 1 */
typedef struct {
const uint8_t* base;
const uint8_t* end;
const uint8_t* cursor;
} DnsPacket;
static void
_dnsPacket_init( DnsPacket* packet, const uint8_t* buff, int bufflen )
{
packet->base = buff;
packet->end = buff + bufflen;
packet->cursor = buff;
}
static void
_dnsPacket_rewind( DnsPacket* packet )
{
packet->cursor = packet->base;
}
static void
_dnsPacket_skip( DnsPacket* packet, int count )
{
const uint8_t* p = packet->cursor + count;
if (p > packet->end)
p = packet->end;
packet->cursor = p;
}
static int
_dnsPacket_readInt16( DnsPacket* packet )
{
const uint8_t* p = packet->cursor;
if (p+2 > packet->end)
return -1;
packet->cursor = p+2;
return (p[0]<< 8) | p[1];
}
/** QUERY CHECKING
**/
/* check bytes in a dns packet. returns 1 on success, 0 on failure.
* the cursor is only advanced in the case of success
*/
static int
_dnsPacket_checkBytes( DnsPacket* packet, int numBytes, const void* bytes )
{
const uint8_t* p = packet->cursor;
if (p + numBytes > packet->end)
return 0;
if (memcmp(p, bytes, numBytes) != 0)
return 0;
packet->cursor = p + numBytes;
return 1;
}
/* parse and skip a given QNAME stored in a query packet,
* from the current cursor position. returns 1 on success,
* or 0 for malformed data.
*/
static int
_dnsPacket_checkQName( DnsPacket* packet )
{
const uint8_t* p = packet->cursor;
const uint8_t* end = packet->end;
for (;;) {
int c;
if (p >= end)
break;
c = *p++;
if (c == 0) {
packet->cursor = p;
return 1;
}
/* we don't expect label compression in QNAMEs */
if (c >= 64)
break;
p += c;
/* we rely on the bound check at the start
* of the loop here */
}
/* malformed data */
XLOG("malformed QNAME");
return 0;
}
/* parse and skip a given QR stored in a packet.
* returns 1 on success, and 0 on failure
*/
static int
_dnsPacket_checkQR( DnsPacket* packet )
{
if (!_dnsPacket_checkQName(packet))
return 0;
/* TYPE must be one of the things we support */
if (!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_A) &&
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_PTR) &&
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_MX) &&
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_AAAA) &&
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_ALL))
{
XLOG("unsupported TYPE");
return 0;
}
/* CLASS must be IN */
if (!_dnsPacket_checkBytes(packet, 2, DNS_CLASS_IN)) {
XLOG("unsupported CLASS");
return 0;
}
return 1;
}
/* check the header of a DNS Query packet, return 1 if it is one
* type of query we can cache, or 0 otherwise
*/
static int
_dnsPacket_checkQuery( DnsPacket* packet )
{
const uint8_t* p = packet->base;
int qdCount, anCount, dnCount, arCount;
if (p + DNS_HEADER_SIZE > packet->end) {
XLOG("query packet too small");
return 0;
}
/* QR must be set to 0, opcode must be 0 and AA must be 0 */
/* RA, Z, and RCODE must be 0 */
if ((p[2] & 0xFC) != 0 || p[3] != 0) {
XLOG("query packet flags unsupported");
return 0;
}
/* Note that we ignore the TC and RD bits here for the
* following reasons:
*
* - there is no point for a query packet sent to a server
* to have the TC bit set, but the implementation might
* set the bit in the query buffer for its own needs
* between a _resolv_cache_lookup and a
* _resolv_cache_add. We should not freak out if this
* is the case.
*
* - we consider that the result from a RD=0 or a RD=1
* query might be different, hence that the RD bit
* should be used to differentiate cached result.
*
* this implies that RD is checked when hashing or
* comparing query packets, but not TC
*/
/* ANCOUNT, DNCOUNT and ARCOUNT must be 0 */
qdCount = (p[4] << 8) | p[5];
anCount = (p[6] << 8) | p[7];
dnCount = (p[8] << 8) | p[9];
arCount = (p[10]<< 8) | p[11];
if (anCount != 0 || dnCount != 0 || arCount != 0) {
XLOG("query packet contains non-query records");
return 0;
}
if (qdCount == 0) {
XLOG("query packet doesn't contain query record");
return 0;
}
/* Check QDCOUNT QRs */
packet->cursor = p + DNS_HEADER_SIZE;
for (;qdCount > 0; qdCount--)
if (!_dnsPacket_checkQR(packet))
return 0;
return 1;
}
/** QUERY DEBUGGING
**/
#if DEBUG
static char*
_dnsPacket_bprintQName(DnsPacket* packet, char* bp, char* bend)
{
const uint8_t* p = packet->cursor;
const uint8_t* end = packet->end;
int first = 1;
for (;;) {
int c;
if (p >= end)
break;
c = *p++;
if (c == 0) {
packet->cursor = p;
return bp;
}
/* we don't expect label compression in QNAMEs */
if (c >= 64)
break;
if (first)
first = 0;
else
bp = _bprint_c(bp, bend, '.');
bp = _bprint_b(bp, bend, (const char*)p, c);
p += c;
/* we rely on the bound check at the start
* of the loop here */
}
/* malformed data */
bp = _bprint_s(bp, bend, "<MALFORMED>");
return bp;
}
static char*
_dnsPacket_bprintQR(DnsPacket* packet, char* p, char* end)
{
#define QQ(x) { DNS_TYPE_##x, #x }
static const struct {
const char* typeBytes;
const char* typeString;
} qTypes[] =
{
QQ(A), QQ(PTR), QQ(MX), QQ(AAAA), QQ(ALL),
{ NULL, NULL }
};
int nn;
const char* typeString = NULL;
/* dump QNAME */
p = _dnsPacket_bprintQName(packet, p, end);
/* dump TYPE */
p = _bprint_s(p, end, " (");
for (nn = 0; qTypes[nn].typeBytes != NULL; nn++) {
if (_dnsPacket_checkBytes(packet, 2, qTypes[nn].typeBytes)) {
typeString = qTypes[nn].typeString;
break;
}
}
if (typeString != NULL)
p = _bprint_s(p, end, typeString);
else {
int typeCode = _dnsPacket_readInt16(packet);
p = _bprint(p, end, "UNKNOWN-%d", typeCode);
}
p = _bprint_c(p, end, ')');
/* skip CLASS */
_dnsPacket_skip(packet, 2);
return p;
}
/* this function assumes the packet has already been checked */
static char*
_dnsPacket_bprintQuery( DnsPacket* packet, char* p, char* end )
{
int qdCount;
if (packet->base[2] & 0x1) {
p = _bprint_s(p, end, "RECURSIVE ");
}
_dnsPacket_skip(packet, 4);
qdCount = _dnsPacket_readInt16(packet);
_dnsPacket_skip(packet, 6);
for ( ; qdCount > 0; qdCount-- ) {
p = _dnsPacket_bprintQR(packet, p, end);
}
return p;
}
#endif
/** QUERY HASHING SUPPORT
**
** THE FOLLOWING CODE ASSUMES THAT THE INPUT PACKET HAS ALREADY
** BEEN SUCCESFULLY CHECKED.
**/
/* use 32-bit FNV hash function */
#define FNV_MULT 16777619U
#define FNV_BASIS 2166136261U
static unsigned
_dnsPacket_hashBytes( DnsPacket* packet, int numBytes, unsigned hash )
{
const uint8_t* p = packet->cursor;
const uint8_t* end = packet->end;
while (numBytes > 0 && p < end) {
hash = hash*FNV_MULT ^ *p++;
}
packet->cursor = p;
return hash;
}
static unsigned
_dnsPacket_hashQName( DnsPacket* packet, unsigned hash )
{
const uint8_t* p = packet->cursor;
const uint8_t* end = packet->end;
for (;;) {
int c;
if (p >= end) { /* should not happen */
XLOG("%s: INTERNAL_ERROR: read-overflow !!\n", __FUNCTION__);
break;
}
c = *p++;
if (c == 0)
break;
if (c >= 64) {
XLOG("%s: INTERNAL_ERROR: malformed domain !!\n", __FUNCTION__);
break;
}
if (p + c >= end) {
XLOG("%s: INTERNAL_ERROR: simple label read-overflow !!\n",
__FUNCTION__);
break;
}
while (c > 0) {
hash = hash*FNV_MULT ^ *p++;
c -= 1;
}
}
packet->cursor = p;
return hash;
}
static unsigned
_dnsPacket_hashQR( DnsPacket* packet, unsigned hash )
{
hash = _dnsPacket_hashQName(packet, hash);
hash = _dnsPacket_hashBytes(packet, 4, hash); /* TYPE and CLASS */
return hash;
}
static unsigned
_dnsPacket_hashQuery( DnsPacket* packet )
{
unsigned hash = FNV_BASIS;
int count;
_dnsPacket_rewind(packet);
/* we ignore the TC bit for reasons explained in
* _dnsPacket_checkQuery().
*
* however we hash the RD bit to differentiate
* between answers for recursive and non-recursive
* queries.
*/
hash = hash*FNV_MULT ^ (packet->base[2] & 1);
/* assume: other flags are 0 */
_dnsPacket_skip(packet, 4);
/* read QDCOUNT */
count = _dnsPacket_readInt16(packet);
/* assume: ANcount, NScount, ARcount are 0 */
_dnsPacket_skip(packet, 6);
/* hash QDCOUNT QRs */
for ( ; count > 0; count-- )
hash = _dnsPacket_hashQR(packet, hash);
return hash;
}
/** QUERY COMPARISON
**
** THE FOLLOWING CODE ASSUMES THAT THE INPUT PACKETS HAVE ALREADY
** BEEN SUCCESFULLY CHECKED.
**/
static int
_dnsPacket_isEqualDomainName( DnsPacket* pack1, DnsPacket* pack2 )
{
const uint8_t* p1 = pack1->cursor;
const uint8_t* end1 = pack1->end;
const uint8_t* p2 = pack2->cursor;
const uint8_t* end2 = pack2->end;
for (;;) {
int c1, c2;
if (p1 >= end1 || p2 >= end2) {
XLOG("%s: INTERNAL_ERROR: read-overflow !!\n", __FUNCTION__);
break;
}
c1 = *p1++;
c2 = *p2++;
if (c1 != c2)
break;
if (c1 == 0) {
pack1->cursor = p1;
pack2->cursor = p2;
return 1;
}
if (c1 >= 64) {
XLOG("%s: INTERNAL_ERROR: malformed domain !!\n", __FUNCTION__);
break;
}
if ((p1+c1 > end1) || (p2+c1 > end2)) {
XLOG("%s: INTERNAL_ERROR: simple label read-overflow !!\n",
__FUNCTION__);
break;
}
if (memcmp(p1, p2, c1) != 0)
break;
p1 += c1;
p2 += c1;
/* we rely on the bound checks at the start of the loop */
}
/* not the same, or one is malformed */
XLOG("different DN");
return 0;
}
static int
_dnsPacket_isEqualBytes( DnsPacket* pack1, DnsPacket* pack2, int numBytes )
{
const uint8_t* p1 = pack1->cursor;
const uint8_t* p2 = pack2->cursor;
if ( p1 + numBytes > pack1->end || p2 + numBytes > pack2->end )
return 0;
if ( memcmp(p1, p2, numBytes) != 0 )
return 0;
pack1->cursor += numBytes;
pack2->cursor += numBytes;
return 1;
}
static int
_dnsPacket_isEqualQR( DnsPacket* pack1, DnsPacket* pack2 )
{
/* compare domain name encoding + TYPE + CLASS */
if ( !_dnsPacket_isEqualDomainName(pack1, pack2) ||
!_dnsPacket_isEqualBytes(pack1, pack2, 2+2) )
return 0;
return 1;
}
static int
_dnsPacket_isEqualQuery( DnsPacket* pack1, DnsPacket* pack2 )
{
int count1, count2;
/* compare the headers, ignore most fields */
_dnsPacket_rewind(pack1);
_dnsPacket_rewind(pack2);
/* compare RD, ignore TC, see comment in _dnsPacket_checkQuery */
if ((pack1->base[2] & 1) != (pack2->base[2] & 1)) {
XLOG("different RD");
return 0;
}
/* assume: other flags are all 0 */
_dnsPacket_skip(pack1, 4);
_dnsPacket_skip(pack2, 4);
/* compare QDCOUNT */
count1 = _dnsPacket_readInt16(pack1);
count2 = _dnsPacket_readInt16(pack2);
if (count1 != count2 || count1 < 0) {
XLOG("different QDCOUNT");
return 0;
}
/* assume: ANcount, NScount and ARcount are all 0 */
_dnsPacket_skip(pack1, 6);
_dnsPacket_skip(pack2, 6);
/* compare the QDCOUNT QRs */
for ( ; count1 > 0; count1-- ) {
if (!_dnsPacket_isEqualQR(pack1, pack2)) {
XLOG("different QR");
return 0;
}
}
return 1;
}
/****************************************************************************/
/****************************************************************************/
/***** *****/
/***** *****/
/***** *****/
/****************************************************************************/
/****************************************************************************/
/* cache entry. for simplicity, 'hash' and 'hlink' are inlined in this
* structure though they are conceptually part of the hash table.
*
* similarly, mru_next and mru_prev are part of the global MRU list
*/
typedef struct Entry {
unsigned int hash; /* hash value */
struct Entry* hlink; /* next in collision chain */
struct Entry* mru_prev;
struct Entry* mru_next;
const uint8_t* query;
int querylen;
const uint8_t* answer;
int answerlen;
time_t expires; /* time_t when the entry isn't valid any more */
int id; /* for debugging purpose */
} Entry;
/**
* Find the TTL for a negative DNS result. This is defined as the minimum
* of the SOA records TTL and the MINIMUM-TTL field (RFC-2308).
*
* Return 0 if not found.
*/
static u_long
answer_getNegativeTTL(ns_msg handle) {
int n, nscount;
u_long result = 0;
ns_rr rr;
nscount = ns_msg_count(handle, ns_s_ns);
for (n = 0; n < nscount; n++) {
if ((ns_parserr(&handle, ns_s_ns, n, &rr) == 0) && (ns_rr_type(rr) == ns_t_soa)) {
const u_char *rdata = ns_rr_rdata(rr); // find the data
const u_char *edata = rdata + ns_rr_rdlen(rr); // add the len to find the end
int len;
u_long ttl, rec_result = ns_rr_ttl(rr);
// find the MINIMUM-TTL field from the blob of binary data for this record
// skip the server name
len = dn_skipname(rdata, edata);
if (len == -1) continue; // error skipping
rdata += len;
// skip the admin name
len = dn_skipname(rdata, edata);
if (len == -1) continue; // error skipping
rdata += len;
if (edata - rdata != 5*NS_INT32SZ) continue;
// skip: serial number + refresh interval + retry interval + expiry
rdata += NS_INT32SZ * 4;
// finally read the MINIMUM TTL
ttl = ns_get32(rdata);
if (ttl < rec_result) {
rec_result = ttl;
}
// Now that the record is read successfully, apply the new min TTL
if (n == 0 || rec_result < result) {
result = rec_result;
}
}
}
return result;
}
/**
* Parse the answer records and find the appropriate
* smallest TTL among the records. This might be from
* the answer records if found or from the SOA record
* if it's a negative result.
*
* The returned TTL is the number of seconds to
* keep the answer in the cache.
*
* In case of parse error zero (0) is returned which
* indicates that the answer shall not be cached.
*/
static u_long
answer_getTTL(const void* answer, int answerlen)
{
ns_msg handle;
int ancount, n;
u_long result, ttl;
ns_rr rr;
result = 0;
if (ns_initparse(answer, answerlen, &handle) >= 0) {
// get number of answer records
ancount = ns_msg_count(handle, ns_s_an);
if (ancount == 0) {
// a response with no answers? Cache this negative result.
result = answer_getNegativeTTL(handle);
} else {
for (n = 0; n < ancount; n++) {
if (ns_parserr(&handle, ns_s_an, n, &rr) == 0) {
ttl = ns_rr_ttl(rr);
if (n == 0 || ttl < result) {
result = ttl;
}
} else {
XLOG("ns_parserr failed ancount no = %d. errno = %s\n", n, strerror(errno));
}
}
}
} else {
XLOG("ns_parserr failed. %s\n", strerror(errno));
}
XLOG("TTL = %lu\n", result);
return result;
}
static void
entry_free( Entry* e )
{
/* everything is allocated in a single memory block */
if (e) {
free(e);
}
}
static __inline__ void
entry_mru_remove( Entry* e )
{
e->mru_prev->mru_next = e->mru_next;
e->mru_next->mru_prev = e->mru_prev;
}
static __inline__ void
entry_mru_add( Entry* e, Entry* list )
{
Entry* first = list->mru_next;
e->mru_next = first;
e->mru_prev = list;
list->mru_next = e;
first->mru_prev = e;
}
/* compute the hash of a given entry, this is a hash of most
* data in the query (key) */
static unsigned
entry_hash( const Entry* e )
{
DnsPacket pack[1];
_dnsPacket_init(pack, e->query, e->querylen);
return _dnsPacket_hashQuery(pack);
}
/* initialize an Entry as a search key, this also checks the input query packet
* returns 1 on success, or 0 in case of unsupported/malformed data */
static int
entry_init_key( Entry* e, const void* query, int querylen )
{
DnsPacket pack[1];
memset(e, 0, sizeof(*e));
e->query = query;
e->querylen = querylen;
e->hash = entry_hash(e);
_dnsPacket_init(pack, query, querylen);
return _dnsPacket_checkQuery(pack);
}
/* allocate a new entry as a cache node */
static Entry*
entry_alloc( const Entry* init, const void* answer, int answerlen )
{
Entry* e;
int size;
size = sizeof(*e) + init->querylen + answerlen;
e = calloc(size, 1);
if (e == NULL)
return e;
e->hash = init->hash;
e->query = (const uint8_t*)(e+1);
e->querylen = init->querylen;
memcpy( (char*)e->query, init->query, e->querylen );
e->answer = e->query + e->querylen;
e->answerlen = answerlen;
memcpy( (char*)e->answer, answer, e->answerlen );
return e;
}
static int
entry_equals( const Entry* e1, const Entry* e2 )
{
DnsPacket pack1[1], pack2[1];
if (e1->querylen != e2->querylen) {
return 0;
}
_dnsPacket_init(pack1, e1->query, e1->querylen);
_dnsPacket_init(pack2, e2->query, e2->querylen);
return _dnsPacket_isEqualQuery(pack1, pack2);
}
/****************************************************************************/
/****************************************************************************/
/***** *****/
/***** *****/
/***** *****/
/****************************************************************************/
/****************************************************************************/
/* We use a simple hash table with external collision lists
* for simplicity, the hash-table fields 'hash' and 'hlink' are
* inlined in the Entry structure.
*/
/* Maximum time for a thread to wait for an pending request */
#define PENDING_REQUEST_TIMEOUT 20;
typedef struct pending_req_info {
unsigned int hash;
pthread_cond_t cond;
struct pending_req_info* next;
} PendingReqInfo;
typedef struct resolv_cache {
int max_entries;
int num_entries;
Entry mru_list;
int last_id;
Entry* entries;
PendingReqInfo pending_requests;
} Cache;
struct resolv_cache_info {
unsigned netid;
Cache* cache;
struct resolv_cache_info* next;
int nscount;
char* nameservers[MAXNS];
struct addrinfo* nsaddrinfo[MAXNS];
int revision_id; // # times the nameservers have been replaced
struct __res_params params;
struct __res_stats nsstats[MAXNS];
char defdname[MAXDNSRCHPATH];
int dnsrch_offset[MAXDNSRCH+1]; // offsets into defdname
};
#define HTABLE_VALID(x) ((x) != NULL && (x) != HTABLE_DELETED)
static pthread_once_t _res_cache_once = PTHREAD_ONCE_INIT;
static void _res_cache_init(void);
// lock protecting everything in the _resolve_cache_info structs (next ptr, etc)
static pthread_mutex_t _res_cache_list_lock;
/* gets cache associated with a network, or NULL if none exists */
static struct resolv_cache* _find_named_cache_locked(unsigned netid);
static void
_cache_flush_pending_requests_locked( struct resolv_cache* cache )
{
struct pending_req_info *ri, *tmp;
if (cache) {
ri = cache->pending_requests.next;
while (ri) {
tmp = ri;
ri = ri->next;
pthread_cond_broadcast(&tmp->cond);
pthread_cond_destroy(&tmp->cond);
free(tmp);
}
cache->pending_requests.next = NULL;
}
}
/* Return 0 if no pending request is found matching the key.
* If a matching request is found the calling thread will wait until
* the matching request completes, then update *cache and return 1. */
static int
_cache_check_pending_request_locked( struct resolv_cache** cache, Entry* key, unsigned netid )
{
struct pending_req_info *ri, *prev;
int exist = 0;
if (*cache && key) {
ri = (*cache)->pending_requests.next;
prev = &(*cache)->pending_requests;
while (ri) {
if (ri->hash == key->hash) {
exist = 1;
break;
}
prev = ri;
ri = ri->next;
}
if (!exist) {
ri = calloc(1, sizeof(struct pending_req_info));
if (ri) {
ri->hash = key->hash;
pthread_cond_init(&ri->cond, NULL);
prev->next = ri;
}
} else {
struct timespec ts = {0,0};
XLOG("Waiting for previous request");
ts.tv_sec = _time_now() + PENDING_REQUEST_TIMEOUT;
pthread_cond_timedwait(&ri->cond, &_res_cache_list_lock, &ts);
/* Must update *cache as it could have been deleted. */
*cache = _find_named_cache_locked(netid);
}
}
return exist;
}
/* notify any waiting thread that waiting on a request
* matching the key has been added to the cache */
static void
_cache_notify_waiting_tid_locked( struct resolv_cache* cache, Entry* key )
{
struct pending_req_info *ri, *prev;
if (cache && key) {
ri = cache->pending_requests.next;
prev = &cache->pending_requests;
while (ri) {
if (ri->hash == key->hash) {
pthread_cond_broadcast(&ri->cond);
break;
}
prev = ri;
ri = ri->next;
}
// remove item from list and destroy
if (ri) {
prev->next = ri->next;
pthread_cond_destroy(&ri->cond);
free(ri);
}
}
}
/* notify the cache that the query failed */
void
_resolv_cache_query_failed( unsigned netid,
const void* query,
int querylen)
{
Entry key[1];
Cache* cache;
if (!entry_init_key(key, query, querylen))
return;
pthread_mutex_lock(&_res_cache_list_lock);
cache = _find_named_cache_locked(netid);
if (cache) {
_cache_notify_waiting_tid_locked(cache, key);
}
pthread_mutex_unlock(&_res_cache_list_lock);
}
static struct resolv_cache_info* _find_cache_info_locked(unsigned netid);
static void
_cache_flush_locked( Cache* cache )
{
int nn;
for (nn = 0; nn < cache->max_entries; nn++)
{
Entry** pnode = (Entry**) &cache->entries[nn];
while (*pnode != NULL) {
Entry* node = *pnode;
*pnode = node->hlink;
entry_free(node);
}
}
// flush pending request
_cache_flush_pending_requests_locked(cache);
cache->mru_list.mru_next = cache->mru_list.mru_prev = &cache->mru_list;
cache->num_entries = 0;
cache->last_id = 0;
XLOG("*************************\n"
"*** DNS CACHE FLUSHED ***\n"
"*************************");
}
static int
_res_cache_get_max_entries( void )
{
int cache_size = CONFIG_MAX_ENTRIES;
const char* cache_mode = getenv("ANDROID_DNS_MODE");
if (cache_mode == NULL || strcmp(cache_mode, "local") != 0) {
// Don't use the cache in local mode. This is used by the proxy itself.
cache_size = 0;
}
XLOG("cache size: %d", cache_size);
return cache_size;
}
static struct resolv_cache*
_resolv_cache_create( void )
{
struct resolv_cache* cache;
cache = calloc(sizeof(*cache), 1);
if (cache) {
cache->max_entries = _res_cache_get_max_entries();
cache->entries = calloc(sizeof(*cache->entries), cache->max_entries);
if (cache->entries) {
cache->mru_list.mru_prev = cache->mru_list.mru_next = &cache->mru_list;
XLOG("%s: cache created\n", __FUNCTION__);
} else {
free(cache);
cache = NULL;
}
}
return cache;
}
#if DEBUG
static void
_dump_query( const uint8_t* query, int querylen )
{
char temp[256], *p=temp, *end=p+sizeof(temp);
DnsPacket pack[1];
_dnsPacket_init(pack, query, querylen);
p = _dnsPacket_bprintQuery(pack, p, end);
XLOG("QUERY: %s", temp);
}
static void
_cache_dump_mru( Cache* cache )
{
char temp[512], *p=temp, *end=p+sizeof(temp);
Entry* e;
p = _bprint(temp, end, "MRU LIST (%2d): ", cache->num_entries);
for (e = cache->mru_list.mru_next; e != &cache->mru_list; e = e->mru_next)
p = _bprint(p, end, " %d", e->id);
XLOG("%s", temp);
}
static void
_dump_answer(const void* answer, int answerlen)
{
res_state statep;
FILE* fp;
char* buf;
int fileLen;
fp = fopen("/data/reslog.txt", "w+e");
if (fp != NULL) {
statep = __res_get_state();
res_pquery(statep, answer, answerlen, fp);
//Get file length
fseek(fp, 0, SEEK_END);
fileLen=ftell(fp);
fseek(fp, 0, SEEK_SET);
buf = (char *)malloc(fileLen+1);
if (buf != NULL) {
//Read file contents into buffer
fread(buf, fileLen, 1, fp);
XLOG("%s\n", buf);
free(buf);
}
fclose(fp);
remove("/data/reslog.txt");
}
else {
errno = 0; // else debug is introducing error signals
XLOG("%s: can't open file\n", __FUNCTION__);
}
}
#endif
#if DEBUG
# define XLOG_QUERY(q,len) _dump_query((q), (len))
# define XLOG_ANSWER(a, len) _dump_answer((a), (len))
#else
# define XLOG_QUERY(q,len) ((void)0)
# define XLOG_ANSWER(a,len) ((void)0)
#endif
/* This function tries to find a key within the hash table
* In case of success, it will return a *pointer* to the hashed key.
* In case of failure, it will return a *pointer* to NULL
*
* So, the caller must check '*result' to check for success/failure.
*
* The main idea is that the result can later be used directly in
* calls to _resolv_cache_add or _resolv_cache_remove as the 'lookup'
* parameter. This makes the code simpler and avoids re-searching
* for the key position in the htable.
*
* The result of a lookup_p is only valid until you alter the hash
* table.
*/
static Entry**
_cache_lookup_p( Cache* cache,
Entry* key )
{
int index = key->hash % cache->max_entries;
Entry** pnode = (Entry**) &cache->entries[ index ];
while (*pnode != NULL) {
Entry* node = *pnode;
if (node == NULL)
break;
if (node->hash == key->hash && entry_equals(node, key))
break;
pnode = &node->hlink;
}
return pnode;
}
/* Add a new entry to the hash table. 'lookup' must be the
* result of an immediate previous failed _lookup_p() call
* (i.e. with *lookup == NULL), and 'e' is the pointer to the
* newly created entry
*/
static void
_cache_add_p( Cache* cache,
Entry** lookup,
Entry* e )
{
*lookup = e;
e->id = ++cache->last_id;
entry_mru_add(e, &cache->mru_list);
cache->num_entries += 1;
XLOG("%s: entry %d added (count=%d)", __FUNCTION__,
e->id, cache->num_entries);
}
/* Remove an existing entry from the hash table,
* 'lookup' must be the result of an immediate previous
* and succesful _lookup_p() call.
*/
static void
_cache_remove_p( Cache* cache,
Entry** lookup )
{
Entry* e = *lookup;
XLOG("%s: entry %d removed (count=%d)", __FUNCTION__,
e->id, cache->num_entries-1);
entry_mru_remove(e);
*lookup = e->hlink;
entry_free(e);
cache->num_entries -= 1;
}
/* Remove the oldest entry from the hash table.
*/
static void
_cache_remove_oldest( Cache* cache )
{
Entry* oldest = cache->mru_list.mru_prev;
Entry** lookup = _cache_lookup_p(cache, oldest);
if (*lookup == NULL) { /* should not happen */
XLOG("%s: OLDEST NOT IN HTABLE ?", __FUNCTION__);
return;
}
if (DEBUG) {
XLOG("Cache full - removing oldest");
XLOG_QUERY(oldest->query, oldest->querylen);
}
_cache_remove_p(cache, lookup);
}
/* Remove all expired entries from the hash table.
*/
static void _cache_remove_expired(Cache* cache) {
Entry* e;
time_t now = _time_now();
for (e = cache->mru_list.mru_next; e != &cache->mru_list;) {
// Entry is old, remove
if (now >= e->expires) {
Entry** lookup = _cache_lookup_p(cache, e);
if (*lookup == NULL) { /* should not happen */
XLOG("%s: ENTRY NOT IN HTABLE ?", __FUNCTION__);
return;
}
e = e->mru_next;
_cache_remove_p(cache, lookup);
} else {
e = e->mru_next;
}
}
}
ResolvCacheStatus
_resolv_cache_lookup( unsigned netid,
const void* query,
int querylen,
void* answer,
int answersize,
int *answerlen )
{
Entry key[1];
Entry** lookup;
Entry* e;
time_t now;
Cache* cache;
ResolvCacheStatus result = RESOLV_CACHE_NOTFOUND;
XLOG("%s: lookup", __FUNCTION__);
XLOG_QUERY(query, querylen);
/* we don't cache malformed queries */
if (!entry_init_key(key, query, querylen)) {
XLOG("%s: unsupported query", __FUNCTION__);
return RESOLV_CACHE_UNSUPPORTED;
}
/* lookup cache */
pthread_once(&_res_cache_once, _res_cache_init);
pthread_mutex_lock(&_res_cache_list_lock);
cache = _find_named_cache_locked(netid);
if (cache == NULL) {
result = RESOLV_CACHE_UNSUPPORTED;
goto Exit;
}
/* see the description of _lookup_p to understand this.
* the function always return a non-NULL pointer.
*/
lookup = _cache_lookup_p(cache, key);
e = *lookup;
if (e == NULL) {
XLOG( "NOT IN CACHE");
// calling thread will wait if an outstanding request is found
// that matching this query
if (!_cache_check_pending_request_locked(&cache, key, netid) || cache == NULL) {
goto Exit;
} else {
lookup = _cache_lookup_p(cache, key);
e = *lookup;
if (e == NULL) {
goto Exit;
}
}
}
now = _time_now();
/* remove stale entries here */
if (now >= e->expires) {
XLOG( " NOT IN CACHE (STALE ENTRY %p DISCARDED)", *lookup );
XLOG_QUERY(e->query, e->querylen);
_cache_remove_p(cache, lookup);
goto Exit;
}
*answerlen = e->answerlen;
if (e->answerlen > answersize) {
/* NOTE: we return UNSUPPORTED if the answer buffer is too short */
result = RESOLV_CACHE_UNSUPPORTED;
XLOG(" ANSWER TOO LONG");
goto Exit;
}
memcpy( answer, e->answer, e->answerlen );
/* bump up this entry to the top of the MRU list */
if (e != cache->mru_list.mru_next) {
entry_mru_remove( e );
entry_mru_add( e, &cache->mru_list );
}
XLOG( "FOUND IN CACHE entry=%p", e );
result = RESOLV_CACHE_FOUND;
Exit:
pthread_mutex_unlock(&_res_cache_list_lock);
return result;
}
void
_resolv_cache_add( unsigned netid,
const void* query,
int querylen,
const void* answer,
int answerlen )
{
Entry key[1];
Entry* e;
Entry** lookup;
u_long ttl;
Cache* cache = NULL;
/* don't assume that the query has already been cached
*/
if (!entry_init_key( key, query, querylen )) {
XLOG( "%s: passed invalid query ?", __FUNCTION__);
return;
}
pthread_mutex_lock(&_res_cache_list_lock);
cache = _find_named_cache_locked(netid);
if (cache == NULL) {
goto Exit;
}
XLOG( "%s: query:", __FUNCTION__ );
XLOG_QUERY(query,querylen);
XLOG_ANSWER(answer, answerlen);
#if DEBUG_DATA
XLOG( "answer:");
XLOG_BYTES(answer,answerlen);
#endif
lookup = _cache_lookup_p(cache, key);
e = *lookup;
if (e != NULL) { /* should not happen */
XLOG("%s: ALREADY IN CACHE (%p) ? IGNORING ADD",
__FUNCTION__, e);
goto Exit;
}
if (cache->num_entries >= cache->max_entries) {
_cache_remove_expired(cache);
if (cache->num_entries >= cache->max_entries) {
_cache_remove_oldest(cache);
}
/* need to lookup again */
lookup = _cache_lookup_p(cache, key);
e = *lookup;
if (e != NULL) {
XLOG("%s: ALREADY IN CACHE (%p) ? IGNORING ADD",
__FUNCTION__, e);
goto Exit;
}
}
ttl = answer_getTTL(answer, answerlen);
if (ttl > 0) {
e = entry_alloc(key, answer, answerlen);
if (e != NULL) {
e->expires = ttl + _time_now();
_cache_add_p(cache, lookup, e);
}
}
#if DEBUG
_cache_dump_mru(cache);
#endif
Exit:
if (cache != NULL) {
_cache_notify_waiting_tid_locked(cache, key);
}
pthread_mutex_unlock(&_res_cache_list_lock);
}
/****************************************************************************/
/****************************************************************************/
/***** *****/
/***** *****/
/***** *****/
/****************************************************************************/
/****************************************************************************/
// Head of the list of caches. Protected by _res_cache_list_lock.
static struct resolv_cache_info _res_cache_list;
/* insert resolv_cache_info into the list of resolv_cache_infos */
static void _insert_cache_info_locked(struct resolv_cache_info* cache_info);
/* creates a resolv_cache_info */
static struct resolv_cache_info* _create_cache_info( void );
/* gets a resolv_cache_info associated with a network, or NULL if not found */
static struct resolv_cache_info* _find_cache_info_locked(unsigned netid);
/* look up the named cache, and creates one if needed */
static struct resolv_cache* _get_res_cache_for_net_locked(unsigned netid);
/* empty the named cache */
static void _flush_cache_for_net_locked(unsigned netid);
/* empty the nameservers set for the named cache */
static void _free_nameservers_locked(struct resolv_cache_info* cache_info);
/* return 1 if the provided list of name servers differs from the list of name servers
* currently attached to the provided cache_info */
static int _resolv_is_nameservers_equal_locked(struct resolv_cache_info* cache_info,
const char** servers, int numservers);
/* clears the stats samples contained withing the given cache_info */
static void _res_cache_clear_stats_locked(struct resolv_cache_info* cache_info);
static void
_res_cache_init(void)
{
const char* env = getenv(CONFIG_ENV);
if (env && atoi(env) == 0) {
/* the cache is disabled */
return;
}
memset(&_res_cache_list, 0, sizeof(_res_cache_list));
pthread_mutex_init(&_res_cache_list_lock, NULL);
}
static struct resolv_cache*
_get_res_cache_for_net_locked(unsigned netid)
{
struct resolv_cache* cache = _find_named_cache_locked(netid);
if (!cache) {
struct resolv_cache_info* cache_info = _create_cache_info();
if (cache_info) {
cache = _resolv_cache_create();
if (cache) {
cache_info->cache = cache;
cache_info->netid = netid;
_insert_cache_info_locked(cache_info);
} else {
free(cache_info);
}
}
}
return cache;
}
void
_resolv_flush_cache_for_net(unsigned netid)
{
pthread_once(&_res_cache_once, _res_cache_init);
pthread_mutex_lock(&_res_cache_list_lock);
_flush_cache_for_net_locked(netid);
pthread_mutex_unlock(&_res_cache_list_lock);
}
static void
_flush_cache_for_net_locked(unsigned netid)
{
struct resolv_cache* cache = _find_named_cache_locked(netid);
if (cache) {
_cache_flush_locked(cache);
}
// Also clear the NS statistics.
struct resolv_cache_info* cache_info = _find_cache_info_locked(netid);
_res_cache_clear_stats_locked(cache_info);
}
void _resolv_delete_cache_for_net(unsigned netid)
{
pthread_once(&_res_cache_once, _res_cache_init);
pthread_mutex_lock(&_res_cache_list_lock);
struct resolv_cache_info* prev_cache_info = &_res_cache_list;
while (prev_cache_info->next) {
struct resolv_cache_info* cache_info = prev_cache_info->next;
if (cache_info->netid == netid) {
prev_cache_info->next = cache_info->next;
_cache_flush_locked(cache_info->cache);
free(cache_info->cache->entries);
free(cache_info->cache);
_free_nameservers_locked(cache_info);
free(cache_info);
break;
}
prev_cache_info = prev_cache_info->next;
}
pthread_mutex_unlock(&_res_cache_list_lock);
}
static struct resolv_cache_info*
_create_cache_info(void)
{
struct resolv_cache_info* cache_info;
cache_info = calloc(sizeof(*cache_info), 1);
return cache_info;
}
static void
_insert_cache_info_locked(struct resolv_cache_info* cache_info)
{
struct resolv_cache_info* last;
for (last = &_res_cache_list; last->next; last = last->next);
last->next = cache_info;
}
static struct resolv_cache*
_find_named_cache_locked(unsigned netid) {
struct resolv_cache_info* info = _find_cache_info_locked(netid);
if (info != NULL) return info->cache;
return NULL;
}
static struct resolv_cache_info*
_find_cache_info_locked(unsigned netid)
{
struct resolv_cache_info* cache_info = _res_cache_list.next;
while (cache_info) {
if (cache_info->netid == netid) {
break;
}
cache_info = cache_info->next;
}
return cache_info;
}
void
_resolv_set_default_params(struct __res_params* params) {
params->sample_validity = NSSAMPLE_VALIDITY;
params->success_threshold = SUCCESS_THRESHOLD;
params->min_samples = 0;
params->max_samples = 0;
}
int
_resolv_set_nameservers_for_net(unsigned netid, const char** servers, unsigned numservers,
const char *domains, const struct __res_params* params)
{
char sbuf[NI_MAXSERV];
register char *cp;
int *offset;
struct addrinfo* nsaddrinfo[MAXNS];
if (numservers > MAXNS) {
XLOG("%s: numservers=%u, MAXNS=%u", __FUNCTION__, numservers, MAXNS);
return E2BIG;
}
// Parse the addresses before actually locking or changing any state, in case there is an error.
// As a side effect this also reduces the time the lock is kept.
struct addrinfo hints = {
.ai_family = AF_UNSPEC,
.ai_socktype = SOCK_DGRAM,
.ai_flags = AI_NUMERICHOST
};
snprintf(sbuf, sizeof(sbuf), "%u", NAMESERVER_PORT);
for (unsigned i = 0; i < numservers; i++) {
// The addrinfo structures allocated here are freed in _free_nameservers_locked().
int rt = getaddrinfo(servers[i], sbuf, &hints, &nsaddrinfo[i]);
if (rt != 0) {
for (unsigned j = 0 ; j < i ; j++) {
freeaddrinfo(nsaddrinfo[j]);
nsaddrinfo[j] = NULL;
}
XLOG("%s: getaddrinfo(%s)=%s", __FUNCTION__, servers[i], gai_strerror(rt));
return EINVAL;
}
}
pthread_once(&_res_cache_once, _res_cache_init);
pthread_mutex_lock(&_res_cache_list_lock);
// creates the cache if not created
_get_res_cache_for_net_locked(netid);
struct resolv_cache_info* cache_info = _find_cache_info_locked(netid);
if (cache_info != NULL) {
uint8_t old_max_samples = cache_info->params.max_samples;
if (params != NULL) {
cache_info->params = *params;
} else {
_resolv_set_default_params(&cache_info->params);
}
if (!_resolv_is_nameservers_equal_locked(cache_info, servers, numservers)) {
// free current before adding new
_free_nameservers_locked(cache_info);
unsigned i;
for (i = 0; i < numservers; i++) {
cache_info->nsaddrinfo[i] = nsaddrinfo[i];
cache_info->nameservers[i] = strdup(servers[i]);
XLOG("%s: netid = %u, addr = %s\n", __FUNCTION__, netid, servers[i]);
}
cache_info->nscount = numservers;
// Flush the cache and reset the stats.
_flush_cache_for_net_locked(netid);
// increment the revision id to ensure that sample state is not written back if the
// servers change; in theory it would suffice to do so only if the servers or
// max_samples actually change, in practice the overhead of checking is higher than the
// cost, and overflows are unlikely
++cache_info->revision_id;
} else if (cache_info->params.max_samples != old_max_samples) {
// If the maximum number of samples changes, the overhead of keeping the most recent
// samples around is not considered worth the effort, so they are cleared instead. All
// other parameters do not affect shared state: Changing these parameters does not
// invalidate the samples, as they only affect aggregation and the conditions under
// which servers are considered usable.
_res_cache_clear_stats_locked(cache_info);
++cache_info->revision_id;
}
// Always update the search paths, since determining whether they actually changed is
// complex due to the zero-padding, and probably not worth the effort. Cache-flushing
// however is not // necessary, since the stored cache entries do contain the domain, not
// just the host name.
// code moved from res_init.c, load_domain_search_list
strlcpy(cache_info->defdname, domains, sizeof(cache_info->defdname));
if ((cp = strchr(cache_info->defdname, '\n')) != NULL)
*cp = '\0';
cp = cache_info->defdname;
offset = cache_info->dnsrch_offset;
while (offset < cache_info->dnsrch_offset + MAXDNSRCH) {
while (*cp == ' ' || *cp == '\t') /* skip leading white space */
cp++;
if (*cp == '\0') /* stop if nothing more to do */
break;
*offset++ = cp - cache_info->defdname; /* record this search domain */
while (*cp) { /* zero-terminate it */
if (*cp == ' '|| *cp == '\t') {
*cp++ = '\0';
break;
}
cp++;
}
}
*offset = -1; /* cache_info->dnsrch_offset has MAXDNSRCH+1 items */
}
pthread_mutex_unlock(&_res_cache_list_lock);
return 0;
}
static int
_resolv_is_nameservers_equal_locked(struct resolv_cache_info* cache_info,
const char** servers, int numservers)
{
if (cache_info->nscount != numservers) {
return 0;
}
// Compare each name server against current name servers.
// TODO: this is incorrect if the list of current or previous nameservers
// contains duplicates. This does not really matter because the framework
// filters out duplicates, but we should probably fix it. It's also
// insensitive to the order of the nameservers; we should probably fix that
// too.
for (int i = 0; i < numservers; i++) {
for (int j = 0 ; ; j++) {
if (j >= numservers) {
return 0;
}
if (strcmp(cache_info->nameservers[i], servers[j]) == 0) {
break;
}
}
}
return 1;
}
static void
_free_nameservers_locked(struct resolv_cache_info* cache_info)
{
int i;
for (i = 0; i < cache_info->nscount; i++) {
free(cache_info->nameservers[i]);
cache_info->nameservers[i] = NULL;
if (cache_info->nsaddrinfo[i] != NULL) {
freeaddrinfo(cache_info->nsaddrinfo[i]);
cache_info->nsaddrinfo[i] = NULL;
}
cache_info->nsstats[i].sample_count =
cache_info->nsstats[i].sample_next = 0;
}
cache_info->nscount = 0;
_res_cache_clear_stats_locked(cache_info);
++cache_info->revision_id;
}
void
_resolv_populate_res_for_net(res_state statp)
{
if (statp == NULL) {
return;
}
pthread_once(&_res_cache_once, _res_cache_init);
pthread_mutex_lock(&_res_cache_list_lock);
struct resolv_cache_info* info = _find_cache_info_locked(statp->netid);
if (info != NULL) {
int nserv;
struct addrinfo* ai;
XLOG("%s: %u\n", __FUNCTION__, statp->netid);
for (nserv = 0; nserv < MAXNS; nserv++) {
ai = info->nsaddrinfo[nserv];
if (ai == NULL) {
break;
}
if ((size_t) ai->ai_addrlen <= sizeof(statp->_u._ext.ext->nsaddrs[0])) {
if (statp->_u._ext.ext != NULL) {
memcpy(&statp->_u._ext.ext->nsaddrs[nserv], ai->ai_addr, ai->ai_addrlen);
statp->nsaddr_list[nserv].sin_family = AF_UNSPEC;
} else {
if ((size_t) ai->ai_addrlen
<= sizeof(statp->nsaddr_list[0])) {
memcpy(&statp->nsaddr_list[nserv], ai->ai_addr,
ai->ai_addrlen);
} else {
statp->nsaddr_list[nserv].sin_family = AF_UNSPEC;
}
}
} else {
XLOG("%s: found too long addrlen", __FUNCTION__);
}
}
statp->nscount = nserv;
// now do search domains. Note that we cache the offsets as this code runs alot
// but the setting/offset-computer only runs when set/changed
// WARNING: Don't use str*cpy() here, this string contains zeroes.
memcpy(statp->defdname, info->defdname, sizeof(statp->defdname));
register char **pp = statp->dnsrch;
register int *p = info->dnsrch_offset;
while (pp < statp->dnsrch + MAXDNSRCH && *p != -1) {
*pp++ = &statp->defdname[0] + *p++;
}
}
pthread_mutex_unlock(&_res_cache_list_lock);
}
/* Resolver reachability statistics. */
static void
_res_cache_add_stats_sample_locked(struct __res_stats* stats, const struct __res_sample* sample,
int max_samples) {
// Note: This function expects max_samples > 0, otherwise a (harmless) modification of the
// allocated but supposedly unused memory for samples[0] will happen
XLOG("%s: adding sample to stats, next = %d, count = %d", __FUNCTION__,
stats->sample_next, stats->sample_count);
stats->samples[stats->sample_next] = *sample;
if (stats->sample_count < max_samples) {
++stats->sample_count;
}
if (++stats->sample_next >= max_samples) {
stats->sample_next = 0;
}
}
static void
_res_cache_clear_stats_locked(struct resolv_cache_info* cache_info) {
if (cache_info) {
for (int i = 0 ; i < MAXNS ; ++i) {
cache_info->nsstats->sample_count = cache_info->nsstats->sample_next = 0;
}
}
}
int
android_net_res_stats_get_info_for_net(unsigned netid, int* nscount,
struct sockaddr_storage servers[MAXNS], int* dcount, char domains[MAXDNSRCH][MAXDNSRCHPATH],
struct __res_params* params, struct __res_stats stats[MAXNS]) {
int revision_id = -1;
pthread_mutex_lock(&_res_cache_list_lock);
struct resolv_cache_info* info = _find_cache_info_locked(netid);
if (info) {
if (info->nscount > MAXNS) {
pthread_mutex_unlock(&_res_cache_list_lock);
XLOG("%s: nscount %d > MAXNS %d", __FUNCTION__, info->nscount, MAXNS);
errno = EFAULT;
return -1;
}
int i;
for (i = 0; i < info->nscount; i++) {
// Verify that the following assumptions are held, failure indicates corruption:
// - getaddrinfo() may never return a sockaddr > sockaddr_storage
// - all addresses are valid
// - there is only one address per addrinfo thanks to numeric resolution
int addrlen = info->nsaddrinfo[i]->ai_addrlen;
if (addrlen < (int) sizeof(struct sockaddr) ||
addrlen > (int) sizeof(servers[0])) {
pthread_mutex_unlock(&_res_cache_list_lock);
XLOG("%s: nsaddrinfo[%d].ai_addrlen == %d", __FUNCTION__, i, addrlen);
errno = EMSGSIZE;
return -1;
}
if (info->nsaddrinfo[i]->ai_addr == NULL) {
pthread_mutex_unlock(&_res_cache_list_lock);
XLOG("%s: nsaddrinfo[%d].ai_addr == NULL", __FUNCTION__, i);
errno = ENOENT;
return -1;
}
if (info->nsaddrinfo[i]->ai_next != NULL) {
pthread_mutex_unlock(&_res_cache_list_lock);
XLOG("%s: nsaddrinfo[%d].ai_next != NULL", __FUNCTION__, i);
errno = ENOTUNIQ;
return -1;
}
}
*nscount = info->nscount;
for (i = 0; i < info->nscount; i++) {
memcpy(&servers[i], info->nsaddrinfo[i]->ai_addr, info->nsaddrinfo[i]->ai_addrlen);
stats[i] = info->nsstats[i];
}
for (i = 0; i < MAXDNSRCH; i++) {
const char* cur_domain = info->defdname + info->dnsrch_offset[i];
// dnsrch_offset[i] can either be -1 or point to an empty string to indicate the end
// of the search offsets. Checking for < 0 is not strictly necessary, but safer.
// TODO: Pass in a search domain array instead of a string to
// _resolv_set_nameservers_for_net() and make this double check unnecessary.
if (info->dnsrch_offset[i] < 0 ||
((size_t)info->dnsrch_offset[i]) >= sizeof(info->defdname) || !cur_domain[0]) {
break;
}
strlcpy(domains[i], cur_domain, MAXDNSRCHPATH);
}
*dcount = i;
*params = info->params;
revision_id = info->revision_id;
}
pthread_mutex_unlock(&_res_cache_list_lock);
return revision_id;
}
int
_resolv_cache_get_resolver_stats( unsigned netid, struct __res_params* params,
struct __res_stats stats[MAXNS]) {
int revision_id = -1;
pthread_mutex_lock(&_res_cache_list_lock);
struct resolv_cache_info* info = _find_cache_info_locked(netid);
if (info) {
memcpy(stats, info->nsstats, sizeof(info->nsstats));
*params = info->params;
revision_id = info->revision_id;
}
pthread_mutex_unlock(&_res_cache_list_lock);
return revision_id;
}
void
_resolv_cache_add_resolver_stats_sample( unsigned netid, int revision_id, int ns,
const struct __res_sample* sample, int max_samples) {
if (max_samples <= 0) return;
pthread_mutex_lock(&_res_cache_list_lock);
struct resolv_cache_info* info = _find_cache_info_locked(netid);
if (info && info->revision_id == revision_id) {
_res_cache_add_stats_sample_locked(&info->nsstats[ns], sample, max_samples);
}
pthread_mutex_unlock(&_res_cache_list_lock);
}