From: Matt Caswell <matt@openssl.org>
Date: Tue, 19 May 2015 15:03:02 +0000 (+0100)
Subject: Fix off-by-one in BN_rand
X-Git-Tag: OpenSSL_1_0_2b~62
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=c6eb1cbd1e2afbf0e0e9170cb9b5df1ff25bfd14;p=oweals%2Fopenssl.git

Fix off-by-one in BN_rand

If BN_rand is called with |bits| set to 1 and |top| set to 1 then a 1 byte
buffer overflow can occur. There are no such instances within the OpenSSL at
the moment.

Thanks to Mateusz Kocielski (LogicalTrust), Marek Kroemeke, Filip Palian for
discovering and reporting this issue.

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
---

diff --git a/crypto/bn/bn.h b/crypto/bn/bn.h
index 7311c0a8cf..5696965e9a 100644
--- a/crypto/bn/bn.h
+++ b/crypto/bn/bn.h
@@ -916,6 +916,7 @@ void ERR_load_BN_strings(void);
 # define BN_R_ARG2_LT_ARG3                                100
 # define BN_R_BAD_RECIPROCAL                              101
 # define BN_R_BIGNUM_TOO_LONG                             114
+# define BN_R_BITS_TOO_SMALL                              118
 # define BN_R_CALLED_WITH_EVEN_MODULUS                    102
 # define BN_R_DIV_BY_ZERO                                 103
 # define BN_R_ENCODING_ERROR                              104
diff --git a/crypto/bn/bn_err.c b/crypto/bn/bn_err.c
index a9b7f5193b..e7a703826e 100644
--- a/crypto/bn/bn_err.c
+++ b/crypto/bn/bn_err.c
@@ -1,6 +1,6 @@
 /* crypto/bn/bn_err.c */
 /* ====================================================================
- * Copyright (c) 1999-2007 The OpenSSL Project.  All rights reserved.
+ * Copyright (c) 1999-2015 The OpenSSL Project.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -119,6 +119,7 @@ static ERR_STRING_DATA BN_str_reasons[] = {
     {ERR_REASON(BN_R_ARG2_LT_ARG3), "arg2 lt arg3"},
     {ERR_REASON(BN_R_BAD_RECIPROCAL), "bad reciprocal"},
     {ERR_REASON(BN_R_BIGNUM_TOO_LONG), "bignum too long"},
+    {ERR_REASON(BN_R_BITS_TOO_SMALL), "bits too small"},
     {ERR_REASON(BN_R_CALLED_WITH_EVEN_MODULUS), "called with even modulus"},
     {ERR_REASON(BN_R_DIV_BY_ZERO), "div by zero"},
     {ERR_REASON(BN_R_ENCODING_ERROR), "encoding error"},
diff --git a/crypto/bn/bn_rand.c b/crypto/bn/bn_rand.c
index 9e78d4d42a..f9fb2e9e45 100644
--- a/crypto/bn/bn_rand.c
+++ b/crypto/bn/bn_rand.c
@@ -121,6 +121,11 @@ static int bnrand(int pseudorand, BIGNUM *rnd, int bits, int top, int bottom)
     int ret = 0, bit, bytes, mask;
     time_t tim;
 
+    if (bits < 0 || (bits == 1 && top > 0)) {
+        BNerr(BN_F_BNRAND, BN_R_BITS_TOO_SMALL);
+        return 0;
+    }
+
     if (bits == 0) {
         BN_zero(rnd);
         return 1;
@@ -169,7 +174,7 @@ static int bnrand(int pseudorand, BIGNUM *rnd, int bits, int top, int bottom)
     }
 #endif
 
-    if (top != -1) {
+    if (top >= 0) {
         if (top) {
             if (bit == 0) {
                 buf[0] = 1;
diff --git a/doc/crypto/BN_rand.pod b/doc/crypto/BN_rand.pod
index d6b975ccf6..bd6bc86323 100644
--- a/doc/crypto/BN_rand.pod
+++ b/doc/crypto/BN_rand.pod
@@ -24,7 +24,8 @@ most significant bit of the random number can be zero. If B<top> is 0,
 it is set to 1, and if B<top> is 1, the two most significant bits of
 the number will be set to 1, so that the product of two such random
 numbers will always have 2*B<bits> length.  If B<bottom> is true, the
-number will be odd.
+number will be odd. The value of B<bits> must be zero or greater. If B<bits> is
+1 then B<top> cannot also be 1.
 
 BN_pseudo_rand() does the same, but pseudo-random numbers generated by
 this function are not necessarily unpredictable. They can be used for