Consistently call BN_init() before BN_with_flags()

BN_with_flags() preserves the BN_FLG_MALLOCED flag of the destination
which results in a potential use of an uninitialized bit. In practice
this doesn't matter since we don't free the cloned BIGNUMs anyway.

As jsing points out, these are mostly pointless noise and should be
garbage collected. I'll leave that for another rainy day.

Coverity flagged one instance BN_gcd_no_branch(), the rest was found by
the ever so helpful grep(1).

CID 345122

ok jsing

3 files changed, 33 insertions, 15 deletions

diff --git a/src/lib/libcrypto/bn/bn_gcd.c b/src/lib/libcrypto/bn/bn_gcd.c
index 469ae752fb..d756398c8f 100644
--- a/src/lib/libcrypto/bn/bn_gcd.c
+++ b/src/lib/libcrypto/bn/bn_gcd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_gcd.c,v 1.15 2017/01/29 17:49:22 beck Exp $ */
+/* $OpenBSD: bn_gcd.c,v 1.16 2021/12/26 15:16:50 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -576,6 +576,9 @@ BN_mod_inverse_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
         bn_check_top(a);
         bn_check_top(n);
 
+        BN_init(&local_A);
+        BN_init(&local_B);
+
         BN_CTX_start(ctx);
         if ((A = BN_CTX_get(ctx)) == NULL)
                 goto err;
@@ -608,10 +611,12 @@ BN_mod_inverse_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
         A->neg = 0;
 
         if (B->neg || (BN_ucmp(B, A) >= 0)) {
-                /* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
-                 * BN_div_no_branch will be called eventually.
-                 */
+                /*
+                 * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+                 * BN_div_no_branch will be called eventually.
+                 */
                 pB = &local_B;
+                /* BN_init() done at the top of the function. */
                 BN_with_flags(pB, B, BN_FLG_CONSTTIME);
                 if (!BN_nnmod(B, pB, A, ctx))
                         goto err;
@@ -633,10 +638,12 @@ BN_mod_inverse_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
                  *      sign*Y*a  ==  A   (mod |n|)
                  */
 
-                /* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
-                 * BN_div_no_branch will be called eventually.
-                 */
+                /*
+                 * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+                 * BN_div_no_branch will be called eventually.
+                 */
                 pA = &local_A;
+                /* BN_init() done at the top of the function. */
                 BN_with_flags(pA, A, BN_FLG_CONSTTIME);
 
                 /* (D, M) := (A/B, A%B) ... */
@@ -740,6 +747,9 @@ BN_gcd_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
                 goto err;
         R = in;
 
+        BN_init(&local_A);
+        BN_init(&local_B);
+
         bn_check_top(a);
         bn_check_top(n);
 
@@ -768,10 +778,12 @@ BN_gcd_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
         A->neg = 0;
 
         if (B->neg || (BN_ucmp(B, A) >= 0)) {
-                /* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
-                 * BN_div_no_branch will be called eventually.
-                 */
+                /*
+                 * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+                 * BN_div_no_branch will be called eventually.
+                 */
                 pB = &local_B;
+                /* BN_init() done at the top of the function. */
                 BN_with_flags(pB, B, BN_FLG_CONSTTIME);
                 if (!BN_nnmod(B, pB, A, ctx))
                         goto err;
@@ -793,10 +805,12 @@ BN_gcd_no_branch(BIGNUM *in, const BIGNUM *a, const BIGNUM *n,
                  *      sign*Y*a  ==  A   (mod |n|)
                  */
 
-                /* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
-                 * BN_div_no_branch will be called eventually.
-                 */
+                /*
+                 * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+                 * BN_div_no_branch will be called eventually.
+                 */
                 pA = &local_A;
+                /* BN_init() done at the top of the function. */
                 BN_with_flags(pA, A, BN_FLG_CONSTTIME);
 
                 /* (D, M) := (A/B, A%B) ... */
diff --git a/src/lib/libcrypto/rsa/rsa_eay.c b/src/lib/libcrypto/rsa/rsa_eay.c
index 33201a8a8b..e9fc67349b 100644
--- a/src/lib/libcrypto/rsa/rsa_eay.c
+++ b/src/lib/libcrypto/rsa/rsa_eay.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: rsa_eay.c,v 1.51 2019/11/02 13:52:31 jsing Exp $ */
+/* $OpenBSD: rsa_eay.c,v 1.52 2021/12/26 15:16:50 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -753,6 +753,7 @@ RSA_eay_mod_exp(BIGNUM *r0, const BIGNUM *I, RSA *rsa, BN_CTX *ctx)
                 goto err;
 
         /* compute I mod p */
+        BN_init(&c);
         BN_with_flags(&c, I, BN_FLG_CONSTTIME);
 
         if (!BN_mod_ct(r1, &c, rsa->p, ctx))
diff --git a/src/lib/libcrypto/rsa/rsa_gen.c b/src/lib/libcrypto/rsa/rsa_gen.c
index 596eb8eb78..1c37d8ef21 100644
--- a/src/lib/libcrypto/rsa/rsa_gen.c
+++ b/src/lib/libcrypto/rsa/rsa_gen.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: rsa_gen.c,v 1.22 2017/01/29 17:49:23 beck Exp $ */
+/* $OpenBSD: rsa_gen.c,v 1.23 2021/12/26 15:16:50 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -194,12 +194,14 @@ rsa_builtin_keygen(RSA *rsa, int bits, BIGNUM *e_value, BN_GENCB *cb)
         if (!BN_mul(r0, r1, r2, ctx))                   /* (p-1)(q-1) */
                 goto err;
 
+        BN_init(&pr0);
         BN_with_flags(&pr0, r0, BN_FLG_CONSTTIME);
 
         if (!BN_mod_inverse_ct(rsa->d, rsa->e, &pr0, ctx)) /* d */
                 goto err;
 
         /* set up d for correct BN_FLG_CONSTTIME flag */
+        BN_init(&d);
         BN_with_flags(&d, rsa->d, BN_FLG_CONSTTIME);
 
         /* calculate d mod (p-1) */
@@ -211,6 +213,7 @@ rsa_builtin_keygen(RSA *rsa, int bits, BIGNUM *e_value, BN_GENCB *cb)
                 goto err;
 
         /* calculate inverse of q mod p */
+        BN_init(&p);
         BN_with_flags(&p, rsa->p, BN_FLG_CONSTTIME);
         if (!BN_mod_inverse_ct(rsa->iqmp, rsa->q, &p, ctx))
                 goto err;