FAILED: patch "[PATCH] smb: client: Compare MACs in constant time" failed to apply to 6.12-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 26bc83b88bbbf054f0980a4a42047a8d1e210e4c
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026030934-wise-emblaze-4f15@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 26bc83b88bbbf054f0980a4a42047a8d1e210e4c Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@kernel.org>
Date: Tue, 17 Feb 2026 20:27:02 -0800
Subject: [PATCH] smb: client: Compare MACs in constant time

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>

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
@@ -11,6 +11,7 @@
 
 #include <linux/fips.h>
 #include <crypto/md5.h>
+#include <crypto/utils.h>
 #include "cifsproto.h"
 #include "smb1proto.h"
 #include "cifs_debug.h"
@@ -131,7 +132,7 @@ int cifs_verify_signature(struct smb_rqst *rqst,
 /*	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
@@ -20,6 +20,7 @@
 #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"
@@ -617,7 +618,8 @@ smb2_verify_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 	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;