ksmbd: validate session id and tree id in compound request

`smb2_get_msg()` in smb2_get_ksmbd_tcon() and smb2_check_user_session()
will always return the first request smb2 header in a compound request.
if `SMB2_TREE_CONNECT_HE` is the first command in compound request, will
return 0, i.e. The tree id check is skipped.
This patch use ksmbd_req_buf_next() to get current command in compound.

Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-21506
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/server/smb2pdu.c

@@ -87,9 +87,9 @@ struct channel *lookup_chann_list(struct ksmbd_session *sess, struct ksmbd_conn
  */
 int smb2_get_ksmbd_tcon(struct ksmbd_work *work)
 {
-	struct smb2_hdr *req_hdr = smb2_get_msg(work->request_buf);
+	struct smb2_hdr *req_hdr = ksmbd_req_buf_next(work);
 	unsigned int cmd = le16_to_cpu(req_hdr->Command);
-	int tree_id;
+	unsigned int tree_id;
 
 	if (cmd == SMB2_TREE_CONNECT_HE ||
 	    cmd ==  SMB2_CANCEL_HE ||
@@ -114,7 +114,7 @@ int smb2_get_ksmbd_tcon(struct ksmbd_work *work)
 			pr_err("The first operation in the compound does not have tcon\n");
 			return -EINVAL;
 		}
-		if (work->tcon->id != tree_id) {
+		if (tree_id != UINT_MAX && work->tcon->id != tree_id) {
 			pr_err("tree id(%u) is different with id(%u) in first operation\n",
 					tree_id, work->tcon->id);
 			return -EINVAL;
@@ -559,9 +559,9 @@ int smb2_allocate_rsp_buf(struct ksmbd_work *work)
  */
 int smb2_check_user_session(struct ksmbd_work *work)
 {
-	struct smb2_hdr *req_hdr = smb2_get_msg(work->request_buf);
+	struct smb2_hdr *req_hdr = ksmbd_req_buf_next(work);
 	struct ksmbd_conn *conn = work->conn;
-	unsigned int cmd = conn->ops->get_cmd_val(work);
+	unsigned int cmd = le16_to_cpu(req_hdr->Command);
 	unsigned long long sess_id;
 
 	/*
@@ -587,7 +587,7 @@ int smb2_check_user_session(struct ksmbd_work *work)
 			pr_err("The first operation in the compound does not have sess\n");
 			return -EINVAL;
 		}
-		if (work->sess->id != sess_id) {
+		if (sess_id != ULLONG_MAX && work->sess->id != sess_id) {
 			pr_err("session id(%llu) is different with the first operation(%lld)\n",
 					sess_id, work->sess->id);
 			return -EINVAL;