Check for errors in BN_bn2dec()

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

Reviewed-by: Tim Hudson <tjh@openssl.org>
(cherry picked from commit 07bed46f332fce8c1d157689a2cdf915a982ae34)

Conflicts:
	crypto/bn/bn_print.c

diff --git a/crypto/bn/bn_print.c b/crypto/bn/bn_print.c
index bfa31efc56216b24456e1b640882461cf5750861..b44403ecfd2b79093d7fdc2768392a12f5304d5c 100644 (file)
--- a/crypto/bn/bn_print.c
+++ b/crypto/bn/bn_print.c
@@ -111,6 +111,7 @@ 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
@@ -120,9 +121,9 @@ char *BN_bn2dec(const BIGNUM *a)
      */
     i = BN_num_bits(a) * 3;
     num = (i / 10 + i / 1000 + 1) + 1;
-    bn_data =
-        (BN_ULONG *)OPENSSL_malloc((num / BN_DEC_NUM + 1) * sizeof(BN_ULONG));
-    buf = (char *)OPENSSL_malloc(num + 3);
+    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)) {
         BNerr(BN_F_BN_BN2DEC, ERR_R_MALLOC_FAILURE);
         goto err;
@@ -143,7 +144,11 @@ char *BN_bn2dec(const BIGNUM *a)
         i = 0;
         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--;
         /*