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Include CRC compensation attack detector in per-transport state structure

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This commit is contained in:
Damien Miller
2012-09-18 01:17:30 +10:00
committed by Markus Friedl
parent fbbec84071
commit 2a99b71b39
3 changed files with 37 additions and 23 deletions
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40
ssh/deattack.c
View File

@@ -93,13 +93,17 @@ check_crc(u_char *S, u_char *buf, u_int32_t len)
return crc == 0;
}
void
deattack_init(struct deattack_ctx *dctx)
{
bzero(dctx, sizeof(*dctx));
dctx->n = HASH_MINSIZE / HASH_ENTRYSIZE;
}
/* Detect a crc32 compensation attack on a packet */
int
detect_attack(u_char *buf, u_int32_t len)
detect_attack(struct deattack_ctx *dctx, u_char *buf, u_int32_t len)
{
static u_int16_t *h = NULL;
static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
u_int16_t *tmp;
u_int32_t i, j, l, same;
u_char *c, *d;
@@ -107,21 +111,23 @@ detect_attack(u_char *buf, u_int32_t len)
if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
len % SSH_BLOCKSIZE != 0)
return DEATTACK_ERROR;
for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
for (l = dctx->n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
;
if (h == NULL) {
if ((h = calloc(l, HASH_ENTRYSIZE)) == NULL)
if (dctx->h == NULL) {
if ((dctx->h = calloc(l, HASH_ENTRYSIZE)) == NULL)
return DEATTACK_ERROR;
n = l;
dctx->n = l;
} else {
if (l > n) {
if ((tmp = reallocn(h, l, HASH_ENTRYSIZE)) == NULL) {
free(h);
if (l > dctx->n) {
if ((tmp = reallocn(dctx->h, l,
HASH_ENTRYSIZE)) == NULL) {
free(dctx->h);
dctx->h = NULL;
return DEATTACK_ERROR;
}
h = tmp;
n = l;
dctx->h = tmp;
dctx->n = l;
}
}
@@ -138,12 +144,12 @@ detect_attack(u_char *buf, u_int32_t len)
}
return DEATTACK_OK;
}
memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
memset(dctx->h, HASH_UNUSEDCHAR, dctx->n * HASH_ENTRYSIZE);
for (c = buf, same = j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
i = (i + 1) & (n - 1)) {
if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
for (i = HASH(c) & (dctx->n - 1); dctx->h[i] != HASH_UNUSED;
i = (i + 1) & (dctx->n - 1)) {
if (!CMP(c, buf + dctx->h[i] * SSH_BLOCKSIZE)) {
if (++same > MAX_IDENTICAL)
return DEATTACK_DOS_DETECTED;
if (check_crc(c, buf, len))
@@ -152,7 +158,7 @@ detect_attack(u_char *buf, u_int32_t len)
break;
}
}
h[i] = j;
dctx->h[i] = j;
}
return DEATTACK_OK;
}

8
ssh/deattack.h
View File

@@ -28,5 +28,11 @@
#define DEATTACK_DOS_DETECTED 2
#define DEATTACK_ERROR 3
int detect_attack(u_char *, u_int32_t);
struct deattack_ctx {
u_int16_t *h;
u_int32_t n;
};
void deattack_init(struct deattack_ctx *);
int detect_attack(struct deattack_ctx *, u_char *, u_int32_t);
#endif

12
ssh/packet.c
View File

@@ -198,6 +198,9 @@ struct session_state {
/* One-off warning about weak ciphers */
int cipher_warning_done;
/* SSH1 CRC compensation attack detector */
struct deattack_ctx deattack;
TAILQ_HEAD(, packet) outgoing;
};
@@ -279,7 +282,7 @@ ssh_packet_set_connection(struct ssh *ssh, int fd_in, int fd_out)
(const u_char *)"", 0, NULL, 0, CIPHER_DECRYPT)) != 0)
fatal("%s: cipher_init failed: %s", __func__, ssh_err(r));
state->newkeys[MODE_IN] = state->newkeys[MODE_OUT] = NULL;
deattack_init(&state->deattack);
return ssh;
}
@@ -1486,8 +1489,8 @@ ssh_packet_read_poll1(struct ssh *ssh, u_char *typep)
* Ariel Futoransky(futo@core-sdi.com)
*/
if (!state->receive_context.plaintext) {
switch (detect_attack(sshbuf_ptr(state->input),
padded_len)) {
switch (detect_attack(&state->deattack,
sshbuf_ptr(state->input), padded_len)) {
case DEATTACK_OK:
break;
case DEATTACK_DETECTED:
@@ -1498,8 +1501,7 @@ ssh_packet_read_poll1(struct ssh *ssh, u_char *typep)
ssh_packet_disconnect(ssh,
"deattack denial of service detected");
default:
ssh_packet_disconnect(ssh,
"deattack error");
ssh_packet_disconnect(ssh, "deattack error");
}
}