bn/bn_mod.c: harmonize BN_mod_add_quick with original implementation.

New implementation failed to correctly reset r->neg flag. Spotted by
OSSFuzz.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6796)

(cherry picked from commit 70a579ae2f37437a1e02331eeaa84e1b68ba021e)

diff --git a/crypto/bn/bn_mod.c b/crypto/bn/bn_mod.c
index 99929f92783a17d5050000de408d445a20f2b252..e33e3f3eb96036533ca055faace81dc06e89dea5 100644 (file)
--- a/crypto/bn/bn_mod.c
+++ b/crypto/bn/bn_mod.c
@@ -83,6 +83,7 @@ int bn_mod_add_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
         ((volatile BN_ULONG *)tp)[i] = 0;
     }
     r->top = mtop;
+    r->neg = 0;
 
     if (tp != storage)
         OPENSSL_free(tp);