[PATCH] ksmbd: validate the zero field of packet header

[linan666]

From: Li Nan <linan122@xxxxxxxxxx>

The SMB2 Protocol requires that "The first byte of the Direct TCP
transport packet header MUST be zero (0x00)"[1]. Commit 1c1bcf2d3ea0
("ksmbd: validate smb request protocol id") removed the validation of
this 1-byte zero. Add the validation back now.

[1]: [MS-SMB2] - v20230227, page 30.
https://winprotocoldoc.blob.core.windows.net/productionwindowsarchives/MS-SMB2/%5bMS-SMB2%5d-230227.pdf

Fixes: 1c1bcf2d3ea0 ("ksmbd: validate smb request protocol id")
Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
---
 fs/smb/server/smb_common.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/smb/server/smb_common.c b/fs/smb/server/smb_common.c
index 6691ae68af0c..7c98bf699772 100644
--- a/fs/smb/server/smb_common.c
+++ b/fs/smb/server/smb_common.c
@@ -158,8 +158,12 @@ int ksmbd_verify_smb_message(struct ksmbd_work *work)
  */
 bool ksmbd_smb_request(struct ksmbd_conn *conn)
 {
-	__le32 *proto = (__le32 *)smb2_get_msg(conn->request_buf);
+	__le32 *proto;
 
+	if (conn->request_buf[0] != 0)
+		return false;
+
+	proto = (__le32 *)smb2_get_msg(conn->request_buf);
 	if (*proto == SMB2_COMPRESSION_TRANSFORM_ID) {
 		pr_err_ratelimited("smb2 compression not support yet");
 		return false;
-- 
2.39.2