/*
* Dropbear SSH
*
* Copyright (c) 2002,2003 Matt Johnston
* All rights reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE. */
/* Buffer handling routines, designed to avoid overflows/using invalid data */
#include "includes.h"
#include "dbutil.h"
#include "buffer.h"
/* Prevent integer overflows when incrementing buffer position/length.
* Calling functions should check arguments first, but this provides a
* backstop */
#define BUF_MAX_INCR 1000000000
#define BUF_MAX_SIZE 1000000000
/* avoid excessively large numbers, > ~8192 bits */
#define BUF_MAX_MPINT (8240 / 8)
/* Create (malloc) a new buffer of size */
buffer* buf_new(unsigned int size) {
buffer* buf;
if (size > BUF_MAX_SIZE) {
dropbear_exit("buf->size too big");
}
buf = (buffer*)m_malloc(sizeof(buffer));
if (size > 0) {
buf->data = (unsigned char*)m_malloc(size);
} else {
buf->data = NULL;
}
buf->size = size;
buf->pos = 0;
buf->len = 0;
return buf;
}
/* free the buffer's data and the buffer itself */
void buf_free(buffer* buf) {
m_free(buf->data)
m_free(buf);
}
/* overwrite the contents of the buffer to clear it */
void buf_burn(buffer* buf) {
m_burn(buf->data, buf->size);
}
/* resize a buffer, pos and len will be repositioned if required when
* downsizing */
void buf_resize(buffer *buf, unsigned int newsize) {
if (newsize > BUF_MAX_SIZE) {
dropbear_exit("buf->size too big");
}
buf->data = m_realloc(buf->data, newsize);
buf->size = newsize;
buf->len = MIN(newsize, buf->len);
buf->pos = MIN(newsize, buf->pos);
}
/* Create a copy of buf, allocating required memory etc. */
/* The new buffer is sized the same as the length of the source buffer. */
buffer* buf_newcopy(buffer* buf) {
buffer* ret;
ret = buf_new(buf->len);
ret->len = buf->len;
memcpy(ret->data, buf->data, buf->len);
return ret;
}
/* Set the length of the buffer */
void buf_setlen(buffer* buf, unsigned int len) {
if (len > buf->size) {
dropbear_exit("bad buf_setlen");
}
buf->len = len;
}
/* Increment the length of the buffer */
void buf_incrlen(buffer* buf, unsigned int incr) {
if (incr > BUF_MAX_INCR || buf->len + incr > buf->size) {
dropbear_exit("bad buf_incrlen");
}
buf->len += incr;
}
/* Set the position of the buffer */
void buf_setpos(buffer* buf, unsigned int pos) {
if (pos > buf->len) {
dropbear_exit("bad buf_setpos");
}
buf->pos = pos;
}
/* increment the postion by incr, increasing the buffer length if required */
void buf_incrwritepos(buffer* buf, unsigned int incr) {
if (incr > BUF_MAX_INCR || buf->pos + incr > buf->size) {
dropbear_exit("bad buf_incrwritepos");
}
buf->pos += incr;
if (buf->pos > buf->len) {
buf->len = buf->pos;
}
}
/* increment the position by incr, negative values are allowed, to
* decrement the pos*/
void buf_incrpos(buffer* buf, int incr) {
if (incr > BUF_MAX_INCR ||
(unsigned int)((int)buf->pos + incr) > buf->len
|| ((int)buf->pos + incr) < 0) {
dropbear_exit("bad buf_incrpos");
}
buf->pos += incr;
}
/* Get a byte from the buffer and increment the pos */
unsigned char buf_getbyte(buffer* buf) {
/* This check is really just ==, but the >= allows us to check for the
* bad case of pos > len, which should _never_ happen. */
if (buf->pos >= buf->len) {
dropbear_exit("bad buf_getbyte");
}
return buf->data[buf->pos++];
}
/* Get a bool from the buffer and increment the pos */
unsigned char buf_getbool(buffer* buf) {
unsigned char b;
b = buf_getbyte(buf);
if (b != 0)
b = 1;
return b;
}
/* put a byte, incrementing the length if required */
void buf_putbyte(buffer* buf, unsigned char val) {
if (buf->pos >= buf->len) {
buf_incrlen(buf, 1);
}
buf->data[buf->pos] = val;
buf->pos++;
}
/* returns an in-place pointer to the buffer, checking that
* the next len bytes from that position can be used */
unsigned char* buf_getptr(buffer* buf, unsigned int len) {
if (buf->pos + len > buf->len) {
dropbear_exit("bad buf_getptr");
}
return &buf->data[buf->pos];
}
/* like buf_getptr, but checks against total size, not used length.
* This allows writing past the used length, but not past the size */
unsigned char* buf_getwriteptr(buffer* buf, unsigned int len) {
if (buf->pos + len > buf->size) {
dropbear_exit("bad buf_getwriteptr");
}
return &buf->data[buf->pos];
}
/* Return a null-terminated string, it is malloced, so must be free()ed
* Note that the string isn't checked for null bytes, hence the retlen
* may be longer than what is returned by strlen */
unsigned char* buf_getstring(buffer* buf, unsigned int *retlen) {
unsigned int len;
unsigned char* ret;
len = buf_getint(buf);
if (len > MAX_STRING_LEN) {
dropbear_exit("string too long");
}
if (retlen != NULL) {
*retlen = len;
}
ret = m_malloc(len+1);
memcpy(ret, buf_getptr(buf, len), len);
buf_incrpos(buf, len);
ret[len] = '\0';
return ret;
}
/* Just increment the buffer position the same as if we'd used buf_getstring,
* but don't bother copying/malloc()ing for it */
void buf_eatstring(buffer *buf) {
buf_incrpos( buf, buf_getint(buf) );
}
/* Get an uint32 from the buffer and increment the pos */
unsigned int buf_getint(buffer* buf) {
unsigned int ret;
LOAD32H(ret, buf_getptr(buf, 4));
buf_incrpos(buf, 4);
return ret;
}
/* put a 32bit uint into the buffer, incr bufferlen & pos if required */
void buf_putint(buffer* buf, int unsigned val) {
STORE32H(val, buf_getwriteptr(buf, 4));
buf_incrwritepos(buf, 4);
}
/* put a SSH style string into the buffer, increasing buffer len if required */
void buf_putstring(buffer* buf, const unsigned char* str, unsigned int len) {
buf_putint(buf, len);
buf_putbytes(buf, str, len);
}
/* put the set of len bytes into the buffer, incrementing the pos, increasing
* len if required */
void buf_putbytes(buffer *buf, const unsigned char *bytes, unsigned int len) {
memcpy(buf_getwriteptr(buf, len), bytes, len);
buf_incrwritepos(buf, len);
}
/* for our purposes we only need positive (or 0) numbers, so will
* fail if we get negative numbers */
void buf_putmpint(buffer* buf, mp_int * mp) {
unsigned int len, pad = 0;
TRACE(("enter buf_putmpint"))
dropbear_assert(mp != NULL);
if (SIGN(mp) == MP_NEG) {
dropbear_exit("negative bignum");
}
/* zero check */
if (USED(mp) == 1 && DIGIT(mp, 0) == 0) {
len = 0;
} else {
/* SSH spec requires padding for mpints with the MSB set, this code
* implements it */
len = mp_count_bits(mp);
/* if the top bit of MSB is set, we need to pad */
pad = (len%8 == 0) ? 1 : 0;
len = len / 8 + 1; /* don't worry about rounding, we need it for
padding anyway when len%8 == 0 */
}
/* store the length */
buf_putint(buf, len);
/* store the actual value */
if (len > 0) {
if (pad) {
buf_putbyte(buf, 0x00);
}
if (mp_to_unsigned_bin(mp, buf_getwriteptr(buf, len-pad)) != MP_OKAY) {
dropbear_exit("mpint error");
}
buf_incrwritepos(buf, len-pad);
}
TRACE(("leave buf_putmpint"))
}
/* Retrieve an mp_int from the buffer.
* Will fail for -ve since they shouldn't be required here.
* Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
int buf_getmpint(buffer* buf, mp_int* mp) {
unsigned int len;
len = buf_getint(buf);
if (len == 0) {
mp_zero(mp);
return DROPBEAR_SUCCESS;
}
if (len > BUF_MAX_MPINT) {
return DROPBEAR_FAILURE;
}
/* check for negative */
if (*buf_getptr(buf, 1) & (1 << (CHAR_BIT-1))) {
return DROPBEAR_FAILURE;
}
if (mp_read_unsigned_bin(mp, buf_getptr(buf, len), len) != MP_OKAY) {
return DROPBEAR_FAILURE;
}
buf_incrpos(buf, len);
return DROPBEAR_SUCCESS;
}