/*
* Off-the-Record Messaging library
* Copyright (C) 2004-2014 Ian Goldberg, David Goulet, Rob Smits,
* Chris Alexander, Willy Lew, Lisa Du,
* Nikita Borisov
* <otr@cypherpunks.ca>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of version 2.1 of the GNU Lesser General
* Public License as published by the Free Software Foundation.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/* Memory allocation routines for libgcrypt. All of the session key
* information gets allocated through here, so we can wipe it out when
* it's free()d. We don't use the built-in secmem functions of
* libgcrypt because you need to declare a fixed amount of it when you
* start up.
*
* Because "secure" and "insecure" allocations from libgcrypt will get
* handled the same way (since we're not going to be running as root,
* and so won't actually have pinned memory), pretend all allocated
* memory (but just from libgcrypt) is requested secure, and wipe it on
* free(). */
/* Uncomment the following to add a check that our free() and realloc() only
* get called on things returned from our malloc(). */
/* #define OTRL_MEM_MAGIC 0x31415926 */
/* system headers */
#ifdef OTRL_MEM_MAGIC
#include <stdio.h>
#endif
#include <stdlib.h>
/* libgcrypt headers */
#include <gcrypt.h>
/* libotr headers */
#include "mem.h"
static size_t header_size;
static void *otrl_mem_malloc(size_t n)
{
void *p;
size_t new_n = n;
new_n += header_size;
/* Check for overflow attack */
if (new_n < n) return NULL;
p = malloc(new_n);
if (p == NULL) return NULL;
((size_t *)p)[0] = new_n; /* Includes header size */
#ifdef OTRL_MEM_MAGIC
((size_t *)p)[1] = OTRL_MEM_MAGIC;
#endif
return (void *)((char *)p + header_size);
}
static int otrl_mem_is_secure(const void *p)
{
return 1;
}
static void otrl_mem_free(void *p)
{
void *real_p = (void *)((char *)p - header_size);
size_t n = ((size_t *)real_p)[0];
#ifdef OTRL_MEM_MAGIC
if (((size_t *)real_p)[1] != OTRL_MEM_MAGIC) {
fprintf(stderr, "Illegal free!\n");
return;
}
#endif
/* Wipe the memory (in the same way the built-in deallocator in
* libgcrypt would) */
memset(real_p, 0xff, n);
memset(real_p, 0xaa, n);
memset(real_p, 0x55, n);
memset(real_p, 0x00, n);
free(real_p);
}
static void *otrl_mem_realloc(void *p, size_t n)
{
if (p == NULL) {
return otrl_mem_malloc(n);
} else if (n == 0) {
otrl_mem_free(p);
return NULL;
} else {
void *real_p = (void *)((char *)p - header_size);
void *new_p;
size_t old_n = ((size_t *)real_p)[0];
#ifdef OTRL_MEM_MAGIC
size_t magic = ((size_t *)real_p)[1];
#endif
size_t new_n = n;
new_n += header_size;
/* Check for overflow attack */
if (new_n < n) return NULL;
#ifdef OTRL_MEM_MAGIC
if (magic != OTRL_MEM_MAGIC) {
fprintf(stderr, "Illegal realloc!\n");
return NULL;
}
#endif
if (new_n < old_n) {
/* Overwrite the space we're about to stop using */
void *p = (void *)((char *)real_p + new_n);
size_t excess = old_n - new_n;
memset(p, 0xff, excess);
memset(p, 0xaa, excess);
memset(p, 0x55, excess);
memset(p, 0x00, excess);
/* We don't actually need to realloc() */
new_p = real_p;
} else {
new_p = realloc(real_p, new_n);
if (new_p == NULL) return NULL;
}
((size_t *)new_p)[0] = new_n; /* Includes header size */
return (void *)((char *)new_p + header_size);
}
}
void otrl_mem_init(void)
{
header_size = 8;
#ifdef OTRL_MEM_MAGIC
if (header_size < 2*sizeof(size_t)) {
header_size = 2*sizeof(size_t);
}
#else
if (header_size < sizeof(size_t)) {
header_size = sizeof(size_t);
}
#endif
gcry_set_allocation_handler(
otrl_mem_malloc,
otrl_mem_malloc,
otrl_mem_is_secure,
otrl_mem_realloc,
otrl_mem_free
);
}
/* Compare two memory blocks in time dependent on the length of the
* blocks, but not their contents. Returns 1 if they differ, 0 if they
* are the same. */
int otrl_mem_differ(const unsigned char *buf1, const unsigned char *buf2,
size_t len)
{
volatile unsigned char diff = 0;
size_t i;
for (i = 0; i < len; ++i) {
diff |= (buf1[i] ^ buf2[i]);
}
return (diff != 0);
}
