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Check for errors in BN_bn2dec()

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If an oversize BIGNUM is presented to BN_bn2dec() it can cause
BN_div_word() to fail and not reduce the value of 't' resulting
in OOB writes to the bn_data buffer and eventually crashing.

Fix by checking return value of BN_div_word() and checking writes
don't overflow buffer.

Thanks to Shi Lei for reporting this bug.

CVE-2016-2182

(Imported from upstream's e36f27ddb80a48e579783bc29fb3758988342b71.)

Change-Id: Ib9078921b4460952c4aa5a6b03ec39a03704bb90
Reviewed-on: https://boringssl-review.googlesource.com/10367
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>
This commit is contained in:
David Benjamin 2016-08-16 02:01:54 -04:00 committed by CQ bot account: commit-bot@chromium.org
parent 722ba2db77
commit 958aaf1ea1
1 changed files with 9 additions and 1 deletions
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10
crypto/bn/convert.c
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@ -375,6 +375,7 @@ char *BN_bn2dec(const BIGNUM *a) {
char *p;
BIGNUM *t = NULL;
BN_ULONG *bn_data = NULL, *lp;
int bn_data_num;
/* get an upper bound for the length of the decimal integer
* num <= (BN_num_bits(a) + 1) * log(2)
@ -383,7 +384,8 @@ char *BN_bn2dec(const BIGNUM *a) {
*/
i = BN_num_bits(a) * 3;
num = i / 10 + i / 1000 + 1 + 1;
bn_data = OPENSSL_malloc((num / BN_DEC_NUM + 1) * sizeof(BN_ULONG));
bn_data_num = num / BN_DEC_NUM + 1;
bn_data = OPENSSL_malloc(bn_data_num * sizeof(BN_ULONG));
buf = OPENSSL_malloc(num + 3);
if ((buf == NULL) || (bn_data == NULL)) {
OPENSSL_PUT_ERROR(BN, ERR_R_MALLOC_FAILURE);
@ -408,7 +410,13 @@ char *BN_bn2dec(const BIGNUM *a) {
} else {
while (!BN_is_zero(t)) {
*lp = BN_div_word(t, BN_DEC_CONV);
if (*lp == (BN_ULONG)-1) {
goto err;
}
lp++;
if (lp - bn_data >= bn_data_num) {
goto err;
}
}
lp--;
/* We now have a series of blocks, BN_DEC_NUM chars