Ensure that the addition mods[i]+delta cannot overflow in probable_prime().

[Problem pointed out by Adam Young <adamy (at) acm.org>]

diff --git a/crypto/bn/bn_prime.c b/crypto/bn/bn_prime.c
index d57f6582110f6c74bec114939fa51ca4cf42a25a..5bab019553bf2ecf3486e46c561c01408520be89 100644 (file)
--- a/crypto/bn/bn_prime.c
+++ b/crypto/bn/bn_prime.c
@@ -378,13 +378,14 @@ static int probable_prime(BIGNUM *rnd, int bits)
        {
        int i;
        BN_ULONG mods[NUMPRIMES];
-       BN_ULONG delta,d;
+       BN_ULONG delta,maxdelta;
 
 again:
        if (!BN_rand(rnd,bits,1,1)) return(0);
        /* we now have a random number 'rand' to test. */
        for (i=1; i<NUMPRIMES; i++)
                mods[i]=BN_mod_word(rnd,(BN_ULONG)primes[i]);
+       maxdelta=BN_MASK2 - primes[NUMPRIMES-1];
        delta=0;
        loop: for (i=1; i<NUMPRIMES; i++)
                {
@@ -392,12 +393,8 @@ again:
                 * that gcd(rnd-1,primes) == 1 (except for 2) */
                if (((mods[i]+delta)%primes[i]) <= 1)
                        {
-                       d=delta;
                        delta+=2;
-                       /* perhaps need to check for overflow of
-                        * delta (but delta can be up to 2^32)
-                        * 21-May-98 eay - added overflow check */
-                       if (delta < d) goto again;
+                       if (delta > maxdelta) goto again;
                        goto loop;
                        }
                }