[PATCH net-next v3 2/5] sctp: Fix MAC comparison to be constant-time

To prevent timing attacks, MACs need to be compared in constant time.
Use the appropriate helper function for this.

Fixes: bbd0d59809f9 ("[SCTP]: Implement the receive and verification of AUTH chunk")
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: [email protected]
Signed-off-by: Eric Biggers <[email protected]>
---
 net/sctp/sm_make_chunk.c | 3 ++-
 net/sctp/sm_statefuns.c  | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 3ead591c72fd3..d099b605e44a7 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -29,10 +29,11 @@
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <crypto/hash.h>
+#include <crypto/utils.h>
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/ip.h>
 #include <linux/ipv6.h>
 #include <linux/net.h>
@@ -1786,11 +1787,11 @@ struct sctp_association *sctp_unpack_cookie(
 			*error = -SCTP_IERROR_NOMEM;
 			goto fail;
 		}
 	}
 
-	if (memcmp(digest, cookie->signature, SCTP_SIGNATURE_SIZE)) {
+	if (crypto_memneq(digest, cookie->signature, SCTP_SIGNATURE_SIZE)) {
 		*error = -SCTP_IERROR_BAD_SIG;
 		goto fail;
 	}
 
 no_hmac:
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index a0524ba8d7878..d4d5b14b49b3f 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -28,10 +28,11 @@
  *    Kevin Gao		    <[email protected]>
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <crypto/utils.h>
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/ip.h>
 #include <linux/ipv6.h>
 #include <linux/net.h>
@@ -4414,11 +4415,11 @@ static enum sctp_ierror sctp_sf_authenticate(
 	sctp_auth_calculate_hmac(asoc, chunk->skb,
 				 (struct sctp_auth_chunk *)chunk->chunk_hdr,
 				 sh_key, GFP_ATOMIC);
 
 	/* Discard the packet if the digests do not match */
-	if (memcmp(save_digest, digest, sig_len)) {
+	if (crypto_memneq(save_digest, digest, sig_len)) {
 		kfree(save_digest);
 		return SCTP_IERROR_BAD_SIG;
 	}
 
 	kfree(save_digest);
-- 
2.50.1