ksmbd: do not expire session on binding failure

ksmbd: do not expire session on binding failure

When a multichannel session binding request fails (e.g. wrong password),
the error path unconditionally sets sess->state = SMB2_SESSION_EXPIRED.
However, during binding, sess points to the target session looked up via
ksmbd_session_lookup_slowpath() -- which belongs to another connection's
user. This allows a remote attacker to invalidate any active session by
simply sending a binding request with a wrong password (DoS).

Fix this by skipping session expiration when the failed request was
a binding attempt, since the session does not belong to the current
connection. The reference taken by ksmbd_session_lookup_slowpath() is
still correctly released via ksmbd_user_session_put().

Cc: stable@vger.kernel.org
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>