[PATCH 6.18] smb: client: Compare MACs in constant time

[PATCH 6.18] smb: client: Compare MACs in constant time

[Eric Biggers]

commit 26bc83b88bbbf054f0980a4a42047a8d1e210e4c upstream.

To prevent timing attacks, MAC comparisons need to be constant-time.
Replace the memcmp() with the correct function, crypto_memneq().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/smb/client/cifsencrypt.c   | 3 ++-
 fs/smb/client/smb2transport.c | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/smb/client/cifsencrypt.c b/fs/smb/client/cifsencrypt.c
index 801824825ecf2..b9e20bcaa8b5c 100644
--- a/fs/smb/client/cifsencrypt.c
+++ b/fs/smb/client/cifsencrypt.c
@@ -24,10 +24,11 @@
 #include <linux/iov_iter.h>
 #include <crypto/aead.h>
 #include <crypto/arc4.h>
 #include <crypto/md5.h>
 #include <crypto/sha2.h>
+#include <crypto/utils.h>
 
 static int cifs_sig_update(struct cifs_calc_sig_ctx *ctx,
 			   const u8 *data, size_t len)
 {
 	if (ctx->md5) {
@@ -275,11 +276,11 @@ int cifs_verify_signature(struct smb_rqst *rqst,
 		return rc;
 
 /*	cifs_dump_mem("what we think it should be: ",
 		      what_we_think_sig_should_be, 16); */
 
-	if (memcmp(server_response_sig, what_we_think_sig_should_be, 8))
+	if (crypto_memneq(server_response_sig, what_we_think_sig_should_be, 8))
 		return -EACCES;
 	else
 		return 0;
 
 }
diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c
index 6a9b80385b86b..211305d43f8d4 100644
--- a/fs/smb/client/smb2transport.c
+++ b/fs/smb/client/smb2transport.c
@@ -18,10 +18,11 @@
 #include <asm/processor.h>
 #include <linux/mempool.h>
 #include <linux/highmem.h>
 #include <crypto/aead.h>
 #include <crypto/sha2.h>
+#include <crypto/utils.h>
 #include "cifsglob.h"
 #include "cifsproto.h"
 #include "smb2proto.h"
 #include "cifs_debug.h"
 #include "../common/smb2status.h"
@@ -615,11 +616,12 @@ smb2_verify_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 	rc = smb3_calc_signature(rqst, server, true);
 
 	if (rc)
 		return rc;
 
-	if (memcmp(server_response_sig, shdr->Signature, SMB2_SIGNATURE_SIZE)) {
+	if (crypto_memneq(server_response_sig, shdr->Signature,
+			  SMB2_SIGNATURE_SIZE)) {
 		cifs_dbg(VFS, "sign fail cmd 0x%x message id 0x%llx\n",
 			shdr->Command, shdr->MessageId);
 		return -EACCES;
 	} else
 		return 0;

base-commit: 6258e292d7463f96d0f06dff2a39093a54c9d16f
-- 
2.53.0