linux-kernel - [PATCH 3/4] perf_event: remove redundant zero fill

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Message-ID: <4B086547.5040100@freemail.hu>
Date:	Sat, 21 Nov 2009 23:10:15 +0100
From:	Németh Márton <nm127@...email.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>
CC:	cocci@...u.dk, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/4] perf_event: remove redundant zero fill

From: Márton Németh <nm127@...email.hu>

The buffer is first zeroed out by memset(). Then strncpy() is used to
fill the content. The strncpy() function also pads the string till the
end of the specified length, which is redundant. The strncpy() does not
ensures that the string will be properly closed with 0. Use strlcpy()
instead.

The semantic match that finds this kind of pattern is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression buffer;
expression size;
expression str;
@@
	memset(buffer, 0, size);
	...
-	strncpy(
+	strlcpy(
	buffer, str, sizeof(buffer)
	);
@@
expression buffer;
expression size;
expression str;
@@
	memset(&buffer, 0, size);
	...
-	strncpy(
+	strlcpy(
	&buffer, str, sizeof(buffer));
@@
expression buffer;
identifier field;
expression size;
expression str;
@@
	memset(buffer, 0, size);
	...
-	strncpy(
+	strlcpy(
	buffer->field, str, sizeof(buffer->field)
	);
@@
expression buffer;
identifier field;
expression size;
expression str;
@@
	memset(&buffer, 0, size);
	...
-	strncpy(
+	strlcpy(
	buffer.field, str, sizeof(buffer.field));
// </smpl>

On strncpy() vs strlcpy() see http://www.gratisoft.us/todd/papers/strlcpy.html .

Signed-off-by: Márton Németh <nm127@...email.hu>
---
diff -u -p a/kernel/perf_event.c b/kernel/perf_event.c
--- a/kernel/perf_event.c 2009-11-14 07:06:52.000000000 +0100
+++ b/kernel/perf_event.c 2009-11-21 22:15:26.000000000 +0100
@@ -3367,7 +3367,7 @@ static void perf_event_comm_event(struct
 	char comm[TASK_COMM_LEN];

 	memset(comm, 0, sizeof(comm));
-	strncpy(comm, comm_event->task->comm, sizeof(comm));
+	strlcpy(comm, comm_event->task->comm, sizeof(comm));
 	size = ALIGN(strlen(comm)+1, sizeof(u64));

 	comm_event->comm = comm;
--
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