wext: handle NULL extra data in iwe_stream_add_point better

[ Upstream commit 93be2b74 ]

gcc-7 complains that wl3501_cs passes NULL into a function that
then uses the argument as the input for memcpy:

drivers/net/wireless/wl3501_cs.c: In function 'wl3501_get_scan':
include/net/iw_handler.h:559:3: error: argument 2 null where non-null expected [-Werror=nonnull]
   memcpy(stream + point_len, extra, iwe->u.data.length);

This works fine here because iwe->u.data.length is guaranteed to be 0
and the memcpy doesn't actually have an effect.

Making the length check explicit avoids the warning and should have
no other effect here.

Also check the pointer itself, since otherwise we get warnings
elsewhere in the code.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

include/net/iw_handler.h

@@ -556,7 +556,8 @@ iwe_stream_add_point(struct iw_request_info *info, char *stream, char *ends,
 		memcpy(stream + lcp_len,
 		       ((char *) &iwe->u) + IW_EV_POINT_OFF,
 		       IW_EV_POINT_PK_LEN - IW_EV_LCP_PK_LEN);
-		memcpy(stream + point_len, extra, iwe->u.data.length);
+		if (iwe->u.data.length && extra)
+			memcpy(stream + point_len, extra, iwe->u.data.length);
 		stream += event_len;
 	}
 	return stream;