net: use scnprintf() to avoid potential buffer overflow

strlcpy() returns the total length of the string they tried to create, so
we should not use its return value without any check. scnprintf() returns
the number of characters written into @buf not including the trailing '\0',
so use it instead here.
Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethernet/eth.c

@@ -376,7 +376,7 @@ static size_t _format_mac_addr(char *buf, int buflen,
 		cp += scnprintf(cp, buflen - (cp - buf), "%02x", addr[i]);
 		if (i == len - 1)
 			break;
-		cp += strlcpy(cp, ":", buflen - (cp - buf));
+		cp += scnprintf(cp, buflen - (cp - buf), ":");
 	}
 	return cp - buf;
 }
@@ -386,7 +386,7 @@ ssize_t sysfs_format_mac(char *buf, const unsigned char *addr, int len)
 	size_t l;
 
 	l = _format_mac_addr(buf, PAGE_SIZE, addr, len);
-	l += strlcpy(buf + l, "\n", PAGE_SIZE - l);
+	l += scnprintf(buf + l, PAGE_SIZE - l, "\n");
 	return ((ssize_t) l);
 }
 EXPORT_SYMBOL(sysfs_format_mac);