FAILED: patch "[PATCH] smb: client: fix UAF and buffer leak in cifs_check_trans2()" 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 730d0bb19507b9e19c2fe5343109ac618e2fbce5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026090302-harddisk-sinless-6dc1@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From 730d0bb19507b9e19c2fe5343109ac618e2fbce5 Mon Sep 17 00:00:00 2001
From: Frank Sorenson <sorenson@redhat.com>
Date: Wed, 12 Aug 2026 21:39:51 -0500
Subject: [PATCH] smb: client: fix UAF and buffer leak in cifs_check_trans2()
 for malformed secondary T2

When a valid primary TRANSACT2 response has been received (mid->resp_buf
set, mid->multiRsp true) and a subsequent secondary response causes
cifs_check_trans2() to return false -- either because the SMB header is
invalid (malformed != 0) or because check2ndT2() rejects the PDU --
handle_mid() overwrites mid->resp_buf with the new buffer (leaking the
primary buffer) and, because mid->multiRsp is set, skips the
server->smallbuf/bigbuf NULL-out.  When the user thread frees
mid->resp_buf, server->smallbuf or server->bigbuf is left dangling; the
demux thread reuses it for the next packet, resulting in a use-after-free.

Combine both early-exit conditions and, when mid->multiRsp is already
set, abort the pending transaction inline: set multiEnd, call
dequeue_mid() with malformed=true, and return true so handle_mid() exits
without touching mid->resp_buf or the server buffer pointers.

Fixes: 316cf94a910f ("CIFS: Move trans2 processing to ops struct")
Cc: stable@vger.kernel.org # cifs_check_trans2() is in smb1ops.c on kernels < 7.0
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>

diff --git a/fs/smb/client/smb1transport.c b/fs/smb/client/smb1transport.c
index 66daa5a37e4a..42e95cc1bd89 100644
--- a/fs/smb/client/smb1transport.c
+++ b/fs/smb/client/smb1transport.c
@@ -449,10 +449,18 @@ bool
 cifs_check_trans2(struct mid_q_entry *mid, struct TCP_Server_Info *server,
 		  char *buf, int malformed)
 {
-	if (malformed)
-		return false;
-	if (check2ndT2(buf) <= 0)
+	if (malformed || check2ndT2(buf) <= 0) {
+		/* mid->multiRsp blocks the server buf detach in handle_mid();
+		 * returning false here would leak resp_buf and leave a dangling
+		 * server->smallbuf/bigbuf after the user thread frees resp_buf.
+		 */
+		if (mid->multiRsp) {
+			mid->multiEnd = true;
+			dequeue_mid(server, mid, true);
+			return true;
+		}
 		return false;
+	}
 	mid->multiRsp = true;
 	if (mid->resp_buf) {
 		/* merge response - fix up 1st*/