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Randomly allocate chunk_hash() key during first use

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This avoids hash flooding attacks.
This commit is contained in:
Tobias Brunner 2013-03-26 19:25:55 +01:00
parent d1953fe403
commit bed4bc1327
1 changed files with 46 additions and 1 deletions
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47
src/libstrongswan/utils/chunk.c
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@ -16,9 +16,12 @@
*/
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <pthread.h>
#include <ctype.h>
#include "chunk.h"
@ -698,15 +701,56 @@ u_int64_t chunk_mac(chunk_t chunk, u_char *key)
}
/**
* Key used for chunk_hash.
* Secret key allocated randomly during first use.
*/
static u_char key[16];
/**
* Only allocate the key once
*/
static pthread_once_t key_allocated = PTHREAD_ONCE_INIT;
/**
* Allocate a key on first use, we do this manually to avoid dependencies on
* plugins.
*/
static void allocate_key()
{
ssize_t len;
size_t done = 0;
int fd;
fd = open("/dev/urandom", O_RDONLY);
if (fd >= 0)
{
while (done < sizeof(key))
{
len = read(fd, key + done, sizeof(key) - done);
if (len < 0)
{
break;
}
done += len;
}
close(fd);
}
/* on error we use random() to generate the key (better than nothing) */
if (done < sizeof(key))
{
srandom(time(NULL) + getpid());
for (; done < sizeof(key); done++)
{
key[done] = (u_char)random();
}
}
}
/**
* Described in header.
*/
u_int32_t chunk_hash_inc(chunk_t chunk, u_int32_t hash)
{
pthread_once(&key_allocated, allocate_key);
/* we could use a mac of the previous hash, but this is faster */
return chunk_mac_inc(chunk, key, ((u_int64_t)hash) << 32 | hash);
}
@ -716,6 +760,7 @@ u_int32_t chunk_hash_inc(chunk_t chunk, u_int32_t hash)
*/
u_int32_t chunk_hash(chunk_t chunk)
{
pthread_once(&key_allocated, allocate_key);
return chunk_mac(chunk, key);
}