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wifi: check tkip/ccmp mac and crc in constant time avoiding timing side channels

--- a/sys/src/9/pc/wifi.c

+++ b/sys/src/9/pc/wifi.c

@@ -1429,8 +1429,7 @@

 		(ulong)b->wp[2]<<16 |

 		(ulong)b->wp[3]<<24;

 	crc = ~crc;

-	if(ethercrc(b->rp, BLEN(b)) != crc)

-		return -1;

+	crc ^= ethercrc(b->rp, BLEN(b));

 	b->wp -= 8;

 	micsetup(&ms, k->key+16);

@@ -1440,7 +1439,7 @@

 	micupdate(&ms, b->rp, BLEN(b));

 	micfinish(&ms, mic);

-	return memcmp(b->wp, mic, 8) != 0;

+	return tsmemcmp(b->wp, mic, 8) | crc;

 }

 static uchar*

@@ -1561,7 +1560,7 @@

 	for(p = sblock(L, N, 0, b, s), x = t; p < &b[M]; x++, p++)

 		*x ^= *p;

-	return memcmp(m, t, M) != 0;

+	return tsmemcmp(m, t, M);

 }

 static int