perf: arm-ccn: Use scnprintf() for robustness

snprintf() is a hard-to-use function, it's especially difficult to use
it for concatenating substrings in a buffer with a limited size.
Since snprintf() returns the would-be-output size, not the actual
size, the subsequent use of snprintf() may point to the incorrect
position easily.  Although the current code doesn't actually overflow
the buffer, it's an incorrect usage.

This patch replaces such snprintf() calls with a safer version,
scnprintf().

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Will Deacon <will@kernel.org>

drivers/perf/arm-ccn.c

@@ -328,15 +328,15 @@ static ssize_t arm_ccn_pmu_event_show(struct device *dev,
 			struct arm_ccn_pmu_event, attr);
 	ssize_t res;
 
-	res = snprintf(buf, PAGE_SIZE, "type=0x%x", event->type);
+	res = scnprintf(buf, PAGE_SIZE, "type=0x%x", event->type);
 	if (event->event)
-		res += snprintf(buf + res, PAGE_SIZE - res, ",event=0x%x",
+		res += scnprintf(buf + res, PAGE_SIZE - res, ",event=0x%x",
 				event->event);
 	if (event->def)
-		res += snprintf(buf + res, PAGE_SIZE - res, ",%s",
+		res += scnprintf(buf + res, PAGE_SIZE - res, ",%s",
 				event->def);
 	if (event->mask)
-		res += snprintf(buf + res, PAGE_SIZE - res, ",mask=0x%x",
+		res += scnprintf(buf + res, PAGE_SIZE - res, ",mask=0x%x",
 				event->mask);
 
 	/* Arguments required by an event */
@@ -344,25 +344,25 @@ static ssize_t arm_ccn_pmu_event_show(struct device *dev,
 	case CCN_TYPE_CYCLES:
 		break;
 	case CCN_TYPE_XP:
-		res += snprintf(buf + res, PAGE_SIZE - res,
+		res += scnprintf(buf + res, PAGE_SIZE - res,
 				",xp=?,vc=?");
 		if (event->event == CCN_EVENT_WATCHPOINT)
-			res += snprintf(buf + res, PAGE_SIZE - res,
+			res += scnprintf(buf + res, PAGE_SIZE - res,
 					",port=?,dir=?,cmp_l=?,cmp_h=?,mask=?");
 		else
-			res += snprintf(buf + res, PAGE_SIZE - res,
+			res += scnprintf(buf + res, PAGE_SIZE - res,
 					",bus=?");
 
 		break;
 	case CCN_TYPE_MN:
-		res += snprintf(buf + res, PAGE_SIZE - res, ",node=%d", ccn->mn_id);
+		res += scnprintf(buf + res, PAGE_SIZE - res, ",node=%d", ccn->mn_id);
 		break;
 	default:
-		res += snprintf(buf + res, PAGE_SIZE - res, ",node=?");
+		res += scnprintf(buf + res, PAGE_SIZE - res, ",node=?");
 		break;
 	}
 
-	res += snprintf(buf + res, PAGE_SIZE - res, "\n");
+	res += scnprintf(buf + res, PAGE_SIZE - res, "\n");
 
 	return res;
 }