FAILED: patch "[PATCH] ksmbd: transport_ipc: validate payload size before reading" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 6f40e50ceb99fc8ef37e5c56e2ec1d162733fef0
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025102920-mace-herbal-edee@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 6f40e50ceb99fc8ef37e5c56e2ec1d162733fef0 Mon Sep 17 00:00:00 2001
From: Qianchang Zhao <pioooooooooip@gmail.com>
Date: Wed, 22 Oct 2025 15:27:47 +0900
Subject: [PATCH] ksmbd: transport_ipc: validate payload size before reading
 handle

handle_response() dereferences the payload as a 4-byte handle without
verifying that the declared payload size is at least 4 bytes. A malformed
or truncated message from ksmbd.mountd can lead to a 4-byte read past the
declared payload size. Validate the size before dereferencing.

This is a minimal fix to guard the initial handle read.

Fixes: 0626e6641f6b ("cifsd: add server handler for central processing and tranport layers")
Cc: stable@vger.kernel.org
Reported-by: Qianchang Zhao <pioooooooooip@gmail.com>
Signed-off-by: Qianchang Zhao <pioooooooooip@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c
index 46f87fd1ce1c..2c08cccfa680 100644
--- a/fs/smb/server/transport_ipc.c
+++ b/fs/smb/server/transport_ipc.c
@@ -263,10 +263,16 @@ static void ipc_msg_handle_free(int handle)
 
 static int handle_response(int type, void *payload, size_t sz)
 {
-	unsigned int handle = *(unsigned int *)payload;
+	unsigned int handle;
 	struct ipc_msg_table_entry *entry;
 	int ret = 0;
 
+	/* Prevent 4-byte read beyond declared payload size */
+	if (sz < sizeof(unsigned int))
+		return -EINVAL;
+
+	handle = *(unsigned int *)payload;
+
 	ipc_update_last_active();
 	down_read(&ipc_msg_table_lock);
 	hash_for_each_possible(ipc_msg_table, entry, ipc_table_hlist, handle) {