smb: client: validate change notify buffer before copy

smb: client: validate change notify buffer before copy

SMB2_change_notify called smb2_validate_iov() but ignored the return
code, then kmemdup()ed using server provided OutputBufferOffset/Length.

Check the return of smb2_validate_iov() and bail out on error.

Discovered with help from the ZeroPath security tooling.

Signed-off-by: Joshua Rogers <linux@joshua.hu>
Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Cc: stable@vger.kernel.org
Fixes: e3e9463414f61 ("smb3: improve SMB3 change notification support")
Signed-off-by: Steve French <stfrench@microsoft.com>