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

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

[Eric Biggers]

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

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

[Eric Biggers]

On Tue, Feb 17, 2026 at 08:27:02PM -0800, Eric Biggers wrote:
> 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(-)

Any feedback on this?  Just to clarify, this is intended to be taken
through the smb tree.

- Eric

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

[Paulo Alcantara]

Eric Biggers <ebiggers@kernel.org> writes:

> 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(-)

Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>

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

[Steve French]

merged into cifs-2.6.git for-next

On Tue, Mar 3, 2026 at 10:24 AM Paulo Alcantara via samba-technical
<samba-technical@lists.samba.org> wrote:
>
> Eric Biggers <ebiggers@kernel.org> writes:
>
> > 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(-)
>
> Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
>


-- 
Thanks,

Steve