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

[Eric Biggers <ebiggers@kernel.org>]

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
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
 fs/smb/client/smb1encrypt.c   | 3 ++-
 fs/smb/client/smb2transport.c | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/smb/client/smb1encrypt.c b/fs/smb/client/smb1encrypt.c
index 0dbbce2431ff..bf10fdeeedca 100644
--- a/fs/smb/client/smb1encrypt.c
+++ b/fs/smb/client/smb1encrypt.c
@@ -9,10 +9,11 @@
  *
  */
 
 #include <linux/fips.h>
 #include <crypto/md5.h>
+#include <crypto/utils.h>
 #include "cifsproto.h"
 #include "smb1proto.h"
 #include "cifs_debug.h"
 
 /*
@@ -129,11 +130,11 @@ 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 8b9000a83181..81be2b226e26 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: 2961f841b025fb234860bac26dfb7fa7cb0fb122
-- 
2.53.0