CIFS: Fix a possible invalid memory access in smb2_query_symlink()

CIFS: Fix a possible invalid memory access in smb2_query_symlink()

BugLink: http://bugs.launchpad.net/bugs/1615620
commit 7893242e2465aea6f2cbc2639da8fa5ce96e8cc2 upstream.

During following a symbolic link we received err_buf from SMB2_open().
While the validity of SMB2 error response is checked previously
in smb2_check_message() a symbolic link payload is not checked at all.
Fix it by adding such checks.

Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>