FAILED: patch "[PATCH] ksmbd: Compare MACs in constant time" failed to apply to 6.18-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x c5794709bc9105935dbedef8b9cf9c06f2b559fa
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026030935-kimono-shale-cbae@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From c5794709bc9105935dbedef8b9cf9c06f2b559fa Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@kernel.org>
Date: Tue, 17 Feb 2026 20:28:29 -0800
Subject: [PATCH] ksmbd: 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: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/server/Kconfig b/fs/smb/server/Kconfig
index 2775162c535c..12594879cb64 100644
--- a/fs/smb/server/Kconfig
+++ b/fs/smb/server/Kconfig
@@ -13,6 +13,7 @@ config SMB_SERVER
 	select CRYPTO_LIB_MD5
 	select CRYPTO_LIB_SHA256
 	select CRYPTO_LIB_SHA512
+	select CRYPTO_LIB_UTILS
 	select CRYPTO_CMAC
 	select CRYPTO_AEAD2
 	select CRYPTO_CCM
diff --git a/fs/smb/server/auth.c b/fs/smb/server/auth.c
index 580c4d303dc3..5fe8c667c6b1 100644
--- a/fs/smb/server/auth.c
+++ b/fs/smb/server/auth.c
@@ -15,6 +15,7 @@
 #include <crypto/aead.h>
 #include <crypto/md5.h>
 #include <crypto/sha2.h>
+#include <crypto/utils.h>
 #include <linux/random.h>
 #include <linux/scatterlist.h>
 
@@ -165,7 +166,8 @@ int ksmbd_auth_ntlmv2(struct ksmbd_conn *conn, struct ksmbd_session *sess,
 			     ntlmv2_rsp, CIFS_HMAC_MD5_HASH_SIZE,
 			     sess->sess_key);
 
-	if (memcmp(ntlmv2->ntlmv2_hash, ntlmv2_rsp, CIFS_HMAC_MD5_HASH_SIZE) != 0)
+	if (crypto_memneq(ntlmv2->ntlmv2_hash, ntlmv2_rsp,
+			  CIFS_HMAC_MD5_HASH_SIZE))
 		return -EINVAL;
 	return 0;
 }
diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 95901a78951c..743c629fe7ec 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -4,6 +4,7 @@
  *   Copyright (C) 2018 Samsung Electronics Co., Ltd.
  */
 
+#include <crypto/utils.h>
 #include <linux/inetdevice.h>
 #include <net/addrconf.h>
 #include <linux/syscalls.h>
@@ -8880,7 +8881,7 @@ int smb2_check_sign_req(struct ksmbd_work *work)
 	ksmbd_sign_smb2_pdu(work->conn, work->sess->sess_key, iov, 1,
 			    signature);
 
-	if (memcmp(signature, signature_req, SMB2_SIGNATURE_SIZE)) {
+	if (crypto_memneq(signature, signature_req, SMB2_SIGNATURE_SIZE)) {
 		pr_err("bad smb2 signature\n");
 		return 0;
 	}
@@ -8968,7 +8969,7 @@ int smb3_check_sign_req(struct ksmbd_work *work)
 	if (ksmbd_sign_smb3_pdu(conn, signing_key, iov, 1, signature))
 		return 0;
 
-	if (memcmp(signature, signature_req, SMB2_SIGNATURE_SIZE)) {
+	if (crypto_memneq(signature, signature_req, SMB2_SIGNATURE_SIZE)) {
 		pr_err("bad smb2 signature\n");
 		return 0;
 	}