wireless: wext-spy: Fix out-of-bounds warning

Fix the following out-of-bounds warning:

net/wireless/wext-spy.c:178:2: warning: 'memcpy' offset [25, 28] from the object at 'threshold' is out of the bounds of referenced subobject 'low' with type 'struct iw_quality' at offset 20 [-Warray-bounds]

The problem is that the original code is trying to copy data into a
couple of struct members adjacent to each other in a single call to
memcpy(). This causes a legitimate compiler warning because memcpy()
overruns the length of &threshold.low and &spydata->spy_thr_low. As
these are just a couple of struct members, fix this by using direct
assignments, instead of memcpy().

This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().

Link: https://github.com/KSPP/linux/issues/109
Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Link: https://lore.kernel.org/r/20210422200032.GA168995@embeddedor
Signed-off-by: Johannes Berg <[e-mail]>

net/wireless/wext-spy.c

···
 		return -EOPNOTSUPP;
 
 	/* Just do it */
-	memcpy(&(spydata->spy_thr_low), &(threshold->low),
-	       2 * sizeof(struct iw_quality));
+	spydata->spy_thr_low = threshold->low;
+	spydata->spy_thr_high = threshold->high;
 
 	/* Clear flag */
 	memset(spydata->spy_thr_under, '\0', sizeof(spydata->spy_thr_under));
···
 		return -EOPNOTSUPP;
 
 	/* Just do it */
-	memcpy(&(threshold->low), &(spydata->spy_thr_low),
-	       2 * sizeof(struct iw_quality));
+	threshold->low = spydata->spy_thr_low;
+	threshold->high = spydata->spy_thr_high;
 
 	return 0;
 }
···
 	memcpy(threshold.addr.sa_data, address, ETH_ALEN);
 	threshold.addr.sa_family = ARPHRD_ETHER;
 	/* Copy stats */
-	memcpy(&(threshold.qual), wstats, sizeof(struct iw_quality));
+	threshold.qual = *wstats;
 	/* Copy also thresholds */
-	memcpy(&(threshold.low), &(spydata->spy_thr_low),
-	       2 * sizeof(struct iw_quality));
+	threshold.low = spydata->spy_thr_low;
+	threshold.high = spydata->spy_thr_high;
 
 	/* Send event to user space */
 	wireless_send_event(dev, SIOCGIWTHRSPY, &wrqu, (char *) &threshold);