ksmbd: fix race condition between destroy_previous_session() and smb2 operations()

If there is ->PreviousSessionId field in the session setup request,
The session of the previous connection should be destroyed.
During this, if the smb2 operation requests in the previous session are
being processed, a racy issue could happen with ksmbd_destroy_file_table().
This patch sets conn->status to KSMBD_SESS_NEED_RECONNECT to block
incoming  operations and waits until on-going operations are complete
(i.e. idle) before desctorying the previous session.

Fixes: c8efcc7 ("ksmbd: add support for durable handles v1/v2")
Cc: [email protected] # v6.6+
Reported-by: [email protected] # ZDI-CAN-25040
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: namjaejeon

fs/smb/server/connection.c

@@ -165,11 +165,43 @@ void ksmbd_all_conn_set_status(u64 sess_id, u32 status)
 	up_read(&conn_list_lock);
 }
 
-void ksmbd_conn_wait_idle(struct ksmbd_conn *conn, u64 sess_id)
+void ksmbd_conn_wait_idle(struct ksmbd_conn *conn)
 {
 	wait_event(conn->req_running_q, atomic_read(&conn->req_running) < 2);
 }
 
+int ksmbd_conn_wait_idle_sess_id(struct ksmbd_conn *curr_conn, u64 sess_id)
+{
+	struct ksmbd_conn *conn;
+	int rc, retry_count = 0, max_timeout = 120;
+	int rcount = 1;
+
+retry_idle:
+	if (retry_count >= max_timeout)
+		return -EIO;
+
+	down_read(&conn_list_lock);
+	list_for_each_entry(conn, &conn_list, conns_list) {
+		if (conn->binding || xa_load(&conn->sessions, sess_id)) {
+			if (conn == curr_conn)
+				rcount = 2;
+			if (atomic_read(&conn->req_running) >= rcount) {
+				rc = wait_event_timeout(conn->req_running_q,
+					atomic_read(&conn->req_running) < rcount,
+					HZ);
+				if (!rc) {
+					up_read(&conn_list_lock);
+					retry_count++;
+					goto retry_idle;
+				}
+			}
+		}
+	}
+	up_read(&conn_list_lock);
+
+	return 0;
+}
+
 int ksmbd_conn_write(struct ksmbd_work *work)
 {
 	struct ksmbd_conn *conn = work->conn;

fs/smb/server/connection.h

@@ -145,7 +145,8 @@ extern struct list_head conn_list;
 extern struct rw_semaphore conn_list_lock;
 
 bool ksmbd_conn_alive(struct ksmbd_conn *conn);
-void ksmbd_conn_wait_idle(struct ksmbd_conn *conn, u64 sess_id);
+void ksmbd_conn_wait_idle(struct ksmbd_conn *conn);
+int ksmbd_conn_wait_idle_sess_id(struct ksmbd_conn *curr_conn, u64 sess_id);
 struct ksmbd_conn *ksmbd_conn_alloc(void);
 void ksmbd_conn_free(struct ksmbd_conn *conn);
 bool ksmbd_conn_lookup_dialect(struct ksmbd_conn *c);

fs/smb/server/mgmt/user_session.c

@@ -311,6 +311,7 @@ void destroy_previous_session(struct ksmbd_conn *conn,
 {
 	struct ksmbd_session *prev_sess;
 	struct ksmbd_user *prev_user;
+	int err;
 
 	down_write(&sessions_table_lock);
 	down_write(&conn->session_lock);
@@ -325,8 +326,16 @@ void destroy_previous_session(struct ksmbd_conn *conn,
 	    memcmp(user->passkey, prev_user->passkey, user->passkey_sz))
 		goto out;
 
+	ksmbd_all_conn_set_status(id, KSMBD_SESS_NEED_RECONNECT);
+	err = ksmbd_conn_wait_idle_sess_id(conn, id);
+	if (err) {
+		ksmbd_all_conn_set_status(id, KSMBD_SESS_NEED_NEGOTIATE);
+		goto out;
+	}
+
 	ksmbd_destroy_file_table(&prev_sess->file_table);
 	prev_sess->state = SMB2_SESSION_EXPIRED;
+	ksmbd_all_conn_set_status(id, KSMBD_SESS_NEED_NEGOTIATE);
 	ksmbd_launch_ksmbd_durable_scavenger();
 out:
 	up_write(&conn->session_lock);

fs/smb/server/smb2pdu.c

@@ -2213,7 +2213,7 @@ int smb2_session_logoff(struct ksmbd_work *work)
 	ksmbd_conn_unlock(conn);
 
 	ksmbd_close_session_fds(work);
-	ksmbd_conn_wait_idle(conn, sess_id);
+	ksmbd_conn_wait_idle(conn);
 
 	/*
 	 * Re-lookup session to validate if session is deleted