[PATCH] ksmbd: transport_ipc: validate payload size before reading handle

[Qianchang Zhao <pioooooooooip@gmail.com>]

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>
---
 fs/smb/server/transport_ipc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c
index 46f87fd1ce1c..2028de4d3ddf 100644
--- a/fs/smb/server/transport_ipc.c
+++ b/fs/smb/server/transport_ipc.c
@@ -263,6 +263,10 @@ static void ipc_msg_handle_free(int handle)
 
 static int handle_response(int type, void *payload, size_t sz)
 {
+	/* Prevent 4-byte read beyond declared payload size */
+	if (sz < sizeof(unsigned int))
+		return -EINVAL;
+
 	unsigned int handle = *(unsigned int *)payload;
 	struct ipc_msg_table_entry *entry;
 	int ret = 0;
-- 
2.34.1