ksmbd: fix racy issue from session setup and logoff

This racy issue is triggered by sending concurrent session setup and
logoff requests. This patch does not set connection status as
KSMBD_SESS_GOOD if state is KSMBD_SESS_NEED_RECONNECT in session setup.
And relookup session to validate if session is deleted in logoff.

Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-20481, ZDI-CAN-20590, ZDI-CAN-20596
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/connection.c

@@ -56,7 +56,7 @@ struct ksmbd_conn *ksmbd_conn_alloc(void)
 		return NULL;
 
 	conn->need_neg = true;
-	conn->status = KSMBD_SESS_NEW;
+	ksmbd_conn_set_new(conn);
 	conn->local_nls = load_nls("utf8");
 	if (!conn->local_nls)
 		conn->local_nls = load_nls_default();
@@ -147,12 +147,12 @@ int ksmbd_conn_try_dequeue_request(struct ksmbd_work *work)
 	return ret;
 }
 
-static void ksmbd_conn_lock(struct ksmbd_conn *conn)
+void ksmbd_conn_lock(struct ksmbd_conn *conn)
 {
 	mutex_lock(&conn->srv_mutex);
 }
 
-static void ksmbd_conn_unlock(struct ksmbd_conn *conn)
+void ksmbd_conn_unlock(struct ksmbd_conn *conn)
 {
 	mutex_unlock(&conn->srv_mutex);
 }
@@ -243,7 +243,7 @@ bool ksmbd_conn_alive(struct ksmbd_conn *conn)
 	if (!ksmbd_server_running())
 		return false;
 
-	if (conn->status == KSMBD_SESS_EXITING)
+	if (ksmbd_conn_exiting(conn))
 		return false;
 
 	if (kthread_should_stop())
@@ -303,7 +303,7 @@ int ksmbd_conn_handler_loop(void *p)
 		pdu_size = get_rfc1002_len(hdr_buf);
 		ksmbd_debug(CONN, "RFC1002 header %u bytes\n", pdu_size);
 
-		if (conn->status == KSMBD_SESS_GOOD)
+		if (ksmbd_conn_good(conn))
 			max_allowed_pdu_size =
 				SMB3_MAX_MSGSIZE + conn->vals->max_write_size;
 		else
@@ -312,7 +312,7 @@ int ksmbd_conn_handler_loop(void *p)
 		if (pdu_size > max_allowed_pdu_size) {
 			pr_err_ratelimited("PDU length(%u) exceeded maximum allowed pdu size(%u) on connection(%d)\n",
 					pdu_size, max_allowed_pdu_size,
-					conn->status);
+					READ_ONCE(conn->status));
 			break;
 		}
 
@@ -416,7 +416,7 @@ static void stop_sessions(void)
 		if (task)
 			ksmbd_debug(CONN, "Stop session handler %s/%d\n",
 				    task->comm, task_pid_nr(task));
-		conn->status = KSMBD_SESS_EXITING;
+		ksmbd_conn_set_exiting(conn);
 		if (t->ops->shutdown) {
 			read_unlock(&conn_list_lock);
 			t->ops->shutdown(t);

fs/ksmbd/connection.h

@@ -162,6 +162,8 @@ void ksmbd_conn_init_server_callbacks(struct ksmbd_conn_ops *ops);
 int ksmbd_conn_handler_loop(void *p);
 int ksmbd_conn_transport_init(void);
 void ksmbd_conn_transport_destroy(void);
+void ksmbd_conn_lock(struct ksmbd_conn *conn);
+void ksmbd_conn_unlock(struct ksmbd_conn *conn);
 
 /*
  * WARNING
@@ -169,43 +171,48 @@ void ksmbd_conn_transport_destroy(void);
  * This is a hack. We will move status to a proper place once we land
  * a multi-sessions support.
  */
-static inline bool ksmbd_conn_good(struct ksmbd_work *work)
+static inline bool ksmbd_conn_good(struct ksmbd_conn *conn)
 {
-	return work->conn->status == KSMBD_SESS_GOOD;
+	return READ_ONCE(conn->status) == KSMBD_SESS_GOOD;
 }
 
-static inline bool ksmbd_conn_need_negotiate(struct ksmbd_work *work)
+static inline bool ksmbd_conn_need_negotiate(struct ksmbd_conn *conn)
 {
-	return work->conn->status == KSMBD_SESS_NEED_NEGOTIATE;
+	return READ_ONCE(conn->status) == KSMBD_SESS_NEED_NEGOTIATE;
 }
 
-static inline bool ksmbd_conn_need_reconnect(struct ksmbd_work *work)
+static inline bool ksmbd_conn_need_reconnect(struct ksmbd_conn *conn)
 {
-	return work->conn->status == KSMBD_SESS_NEED_RECONNECT;
+	return READ_ONCE(conn->status) == KSMBD_SESS_NEED_RECONNECT;
 }
 
-static inline bool ksmbd_conn_exiting(struct ksmbd_work *work)
+static inline bool ksmbd_conn_exiting(struct ksmbd_conn *conn)
 {
-	return work->conn->status == KSMBD_SESS_EXITING;
+	return READ_ONCE(conn->status) == KSMBD_SESS_EXITING;
 }
 
-static inline void ksmbd_conn_set_good(struct ksmbd_work *work)
+static inline void ksmbd_conn_set_new(struct ksmbd_conn *conn)
 {
-	work->conn->status = KSMBD_SESS_GOOD;
+	WRITE_ONCE(conn->status, KSMBD_SESS_NEW);
 }
 
-static inline void ksmbd_conn_set_need_negotiate(struct ksmbd_work *work)
+static inline void ksmbd_conn_set_good(struct ksmbd_conn *conn)
 {
-	work->conn->status = KSMBD_SESS_NEED_NEGOTIATE;
+	WRITE_ONCE(conn->status, KSMBD_SESS_GOOD);
 }
 
-static inline void ksmbd_conn_set_need_reconnect(struct ksmbd_work *work)
+static inline void ksmbd_conn_set_need_negotiate(struct ksmbd_conn *conn)
 {
-	work->conn->status = KSMBD_SESS_NEED_RECONNECT;
+	WRITE_ONCE(conn->status, KSMBD_SESS_NEED_NEGOTIATE);
 }
 
-static inline void ksmbd_conn_set_exiting(struct ksmbd_work *work)
+static inline void ksmbd_conn_set_need_reconnect(struct ksmbd_conn *conn)
 {
-	work->conn->status = KSMBD_SESS_EXITING;
+	WRITE_ONCE(conn->status, KSMBD_SESS_NEED_RECONNECT);
+}
+
+static inline void ksmbd_conn_set_exiting(struct ksmbd_conn *conn)
+{
+	WRITE_ONCE(conn->status, KSMBD_SESS_EXITING);
 }
 #endif /* __CONNECTION_H__ */

fs/ksmbd/mgmt/user_session.c

@@ -315,6 +315,7 @@ static struct ksmbd_session *__session_create(int protocol)
 	if (ksmbd_init_file_table(&sess->file_table))
 		goto error;
 
+	sess->state = SMB2_SESSION_IN_PROGRESS;
 	set_session_flag(sess, protocol);
 	xa_init(&sess->tree_conns);
 	xa_init(&sess->ksmbd_chann_list);

fs/ksmbd/server.c

@@ -93,7 +93,8 @@ static inline int check_conn_state(struct ksmbd_work *work)
 {
 	struct smb_hdr *rsp_hdr;
 
-	if (ksmbd_conn_exiting(work) || ksmbd_conn_need_reconnect(work)) {
+	if (ksmbd_conn_exiting(work->conn) ||
+	    ksmbd_conn_need_reconnect(work->conn)) {
 		rsp_hdr = work->response_buf;
 		rsp_hdr->Status.CifsError = STATUS_CONNECTION_DISCONNECTED;
 		return 1;

fs/ksmbd/smb2pdu.c

@@ -248,7 +248,7 @@ int init_smb2_neg_rsp(struct ksmbd_work *work)
 
 	rsp = smb2_get_msg(work->response_buf);
 
-	WARN_ON(ksmbd_conn_good(work));
+	WARN_ON(ksmbd_conn_good(conn));
 
 	rsp->StructureSize = cpu_to_le16(65);
 	ksmbd_debug(SMB, "conn->dialect 0x%x\n", conn->dialect);
@@ -277,7 +277,7 @@ int init_smb2_neg_rsp(struct ksmbd_work *work)
 		rsp->SecurityMode |= SMB2_NEGOTIATE_SIGNING_REQUIRED_LE;
 	conn->use_spnego = true;
 
-	ksmbd_conn_set_need_negotiate(work);
+	ksmbd_conn_set_need_negotiate(conn);
 	return 0;
 }
 
@@ -561,7 +561,7 @@ int smb2_check_user_session(struct ksmbd_work *work)
 	    cmd == SMB2_SESSION_SETUP_HE)
 		return 0;
 
-	if (!ksmbd_conn_good(work))
+	if (!ksmbd_conn_good(conn))
 		return -EINVAL;
 
 	sess_id = le64_to_cpu(req_hdr->SessionId);
@@ -594,7 +594,7 @@ static void destroy_previous_session(struct ksmbd_conn *conn,
 
 	prev_sess->state = SMB2_SESSION_EXPIRED;
 	xa_for_each(&prev_sess->ksmbd_chann_list, index, chann)
-		chann->conn->status = KSMBD_SESS_EXITING;
+		ksmbd_conn_set_exiting(chann->conn);
 }
 
 /**
@@ -1051,7 +1051,7 @@ int smb2_handle_negotiate(struct ksmbd_work *work)
 
 	ksmbd_debug(SMB, "Received negotiate request\n");
 	conn->need_neg = false;
-	if (ksmbd_conn_good(work)) {
+	if (ksmbd_conn_good(conn)) {
 		pr_err("conn->tcp_status is already in CifsGood State\n");
 		work->send_no_response = 1;
 		return rc;
@@ -1205,7 +1205,7 @@ int smb2_handle_negotiate(struct ksmbd_work *work)
 	}
 
 	conn->srv_sec_mode = le16_to_cpu(rsp->SecurityMode);
-	ksmbd_conn_set_need_negotiate(work);
+	ksmbd_conn_set_need_negotiate(conn);
 
 err_out:
 	if (rc < 0)
@@ -1628,6 +1628,7 @@ int smb2_sess_setup(struct ksmbd_work *work)
 	rsp->SecurityBufferLength = 0;
 	inc_rfc1001_len(work->response_buf, 9);
 
+	ksmbd_conn_lock(conn);
 	if (!req->hdr.SessionId) {
 		sess = ksmbd_smb2_session_create();
 		if (!sess) {
@@ -1675,6 +1676,12 @@ int smb2_sess_setup(struct ksmbd_work *work)
 			goto out_err;
 		}
 
+		if (ksmbd_conn_need_reconnect(conn)) {
+			rc = -EFAULT;
+			sess = NULL;
+			goto out_err;
+		}
+
 		if (ksmbd_session_lookup(conn, sess_id)) {
 			rc = -EACCES;
 			goto out_err;
@@ -1694,12 +1701,20 @@ int smb2_sess_setup(struct ksmbd_work *work)
 			rc = -ENOENT;
 			goto out_err;
 		}
+
+		if (sess->state == SMB2_SESSION_EXPIRED) {
+			rc = -EFAULT;
+			goto out_err;
+		}
+
+		if (ksmbd_conn_need_reconnect(conn)) {
+			rc = -EFAULT;
+			sess = NULL;
+			goto out_err;
+		}
 	}
 	work->sess = sess;
 
-	if (sess->state == SMB2_SESSION_EXPIRED)
-		sess->state = SMB2_SESSION_IN_PROGRESS;
-
 	negblob_off = le16_to_cpu(req->SecurityBufferOffset);
 	negblob_len = le16_to_cpu(req->SecurityBufferLength);
 	if (negblob_off < offsetof(struct smb2_sess_setup_req, Buffer) ||
@@ -1729,8 +1744,10 @@ int smb2_sess_setup(struct ksmbd_work *work)
 				goto out_err;
 			}
 
-			ksmbd_conn_set_good(work);
-			sess->state = SMB2_SESSION_VALID;
+			if (!ksmbd_conn_need_reconnect(conn)) {
+				ksmbd_conn_set_good(conn);
+				sess->state = SMB2_SESSION_VALID;
+			}
 			kfree(sess->Preauth_HashValue);
 			sess->Preauth_HashValue = NULL;
 		} else if (conn->preferred_auth_mech == KSMBD_AUTH_NTLMSSP) {
@@ -1752,8 +1769,10 @@ int smb2_sess_setup(struct ksmbd_work *work)
 				if (rc)
 					goto out_err;
 
-				ksmbd_conn_set_good(work);
-				sess->state = SMB2_SESSION_VALID;
+				if (!ksmbd_conn_need_reconnect(conn)) {
+					ksmbd_conn_set_good(conn);
+					sess->state = SMB2_SESSION_VALID;
+				}
 				if (conn->binding) {
 					struct preauth_session *preauth_sess;
 
@@ -1819,14 +1838,13 @@ int smb2_sess_setup(struct ksmbd_work *work)
 			if (sess->user && sess->user->flags & KSMBD_USER_FLAG_DELAY_SESSION)
 				try_delay = true;
 
-			xa_erase(&conn->sessions, sess->id);
-			ksmbd_session_destroy(sess);
-			work->sess = NULL;
+			sess->state = SMB2_SESSION_EXPIRED;
 			if (try_delay)
 				ssleep(5);
 		}
 	}
 
+	ksmbd_conn_unlock(conn);
 	return rc;
 }
 
@@ -2050,21 +2068,24 @@ int smb2_session_logoff(struct ksmbd_work *work)
 {
 	struct ksmbd_conn *conn = work->conn;
 	struct smb2_logoff_rsp *rsp = smb2_get_msg(work->response_buf);
-	struct ksmbd_session *sess = work->sess;
+	struct ksmbd_session *sess;
+	struct smb2_logoff_req *req = smb2_get_msg(work->request_buf);
 
 	rsp->StructureSize = cpu_to_le16(4);
 	inc_rfc1001_len(work->response_buf, 4);
 
 	ksmbd_debug(SMB, "request\n");
 
-	/* setting CifsExiting here may race with start_tcp_sess */
-	ksmbd_conn_set_need_reconnect(work);
+	ksmbd_conn_set_need_reconnect(conn);
 	ksmbd_close_session_fds(work);
 	ksmbd_conn_wait_idle(conn);
 
+	/*
+	 * Re-lookup session to validate if session is deleted
+	 * while waiting request complete
+	 */
+	sess = ksmbd_session_lookup(conn, le64_to_cpu(req->hdr.SessionId));
 	if (ksmbd_tree_conn_session_logoff(sess)) {
-		struct smb2_logoff_req *req = smb2_get_msg(work->request_buf);
-
 		ksmbd_debug(SMB, "Invalid tid %d\n", req->hdr.Id.SyncId.TreeId);
 		rsp->hdr.Status = STATUS_NETWORK_NAME_DELETED;
 		smb2_set_err_rsp(work);
@@ -2076,9 +2097,7 @@ int smb2_session_logoff(struct ksmbd_work *work)
 
 	ksmbd_free_user(sess->user);
 	sess->user = NULL;
-
-	/* let start_tcp_sess free connection info now */
-	ksmbd_conn_set_need_negotiate(work);
+	ksmbd_conn_set_need_negotiate(conn);
 	return 0;
 }
 

fs/ksmbd/transport_tcp.c

@@ -333,7 +333,7 @@ static int ksmbd_tcp_readv(struct tcp_transport *t, struct kvec *iov_orig,
 		if (length == -EINTR) {
 			total_read = -ESHUTDOWN;
 			break;
-		} else if (conn->status == KSMBD_SESS_NEED_RECONNECT) {
+		} else if (ksmbd_conn_need_reconnect(conn)) {
 			total_read = -EAGAIN;
 			break;
 		} else if (length == -ERESTARTSYS || length == -EAGAIN) {