cifs: ntstatus_to_dos_map[] is not terminated

Functions that walk the ntstatus_to_dos_map[] array could
run off the end. For example, ntstatus_to_dos() loops
while ntstatus_to_dos_map[].ntstatus is not 0. Granted,
this is mostly theoretical, but could be used as a DOS attack
if the error code in the SMB header is bogus.

[Might consider adding to stable, as this patch is low risk - Steve]
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/netmisc.c

@@ -780,7 +780,9 @@ static const struct {
 	ERRDOS, ERRnoaccess, 0xc0000290}, {
 	ERRDOS, ERRbadfunc, 0xc000029c}, {
 	ERRDOS, ERRsymlink, NT_STATUS_STOPPED_ON_SYMLINK}, {
-	ERRDOS, ERRinvlevel, 0x007c0001}, };
+	ERRDOS, ERRinvlevel, 0x007c0001}, {
+	0, 0, 0 }
+};
 
 /*****************************************************************************
  Print an error message from the status code