[PATCH 3.16 113/192] sunrpc: use constant time memory comparison for mac

[Ben Hutchings]

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>

commit 15a8b93fd5690de017ce665382ea45e5d61811a4 upstream.

Otherwise, we enable a MAC forgery via timing attack.

Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Cc: Anna Schumaker <anna.schumaker@xxxxxxxxxx>
Cc: linux-nfs@xxxxxxxxxxxxxxx
Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/sunrpc/auth_gss/gss_krb5_crypto.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
+++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
@@ -34,6 +34,7 @@
  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  */
 
+#include <crypto/algapi.h>
 #include <linux/err.h>
 #include <linux/types.h>
 #include <linux/mm.h>
@@ -838,7 +839,7 @@ gss_krb5_aes_decrypt(struct krb5_ctx *kc
 	if (ret)
 		goto out_err;
 
-	if (memcmp(pkt_hmac, our_hmac, kctx->gk5e->cksumlength) != 0) {
+	if (crypto_memneq(pkt_hmac, our_hmac, kctx->gk5e->cksumlength) != 0) {
 		ret = GSS_S_BAD_SIG;
 		goto out_err;
 	}