Re: [linux-next:master 4605/11713] kernel/trace/trace_events_synth.c:65:9: warning: 'strncpy' specified bound depends on the length of the source argument

[Tom Zanussi <zanussi@kernel.org>]

On Thu, 2022-03-10 at 11:26 -0500, Steven Rostedt wrote:
> On Thu, 10 Mar 2022 10:08:18 -0600
> Tom Zanussi <zanussi@kernel.org> wrote:
> 
> > This patch is for the last_cmd_set() in trace_events_synth.c, yours
> > is
> > for trace_events_hist.c, which also has last_cmd_set().
> 
> Ug, name confusion :-p
> 
> > 
> > The one in trace_events_synth.c is much simpler, so it seemed to me
> > that strcpy() would be ok there.
> 
> If you are only copying the string, why not just use kstrdup()?

Good point, how about this?

From d106b7f636b40ddc08e03397a363fc489681b9e7 Mon Sep 17 00:00:00 2001
Message-Id: <
d106b7f636b40ddc08e03397a363fc489681b9e7.1646930605.git.zanussi@kernel.org
>
From: Tom Zanussi <zanussi@kernel.org>
Date: Thu, 10 Mar 2022 08:59:30 -0600
Subject: [PATCH] tracing: Fix strncpy warning in trace_events_synth.c

0-day reported the strncpy error below:

../kernel/trace/trace_events_synth.c: In function 'last_cmd_set':
../kernel/trace/trace_events_synth.c:65:9: warning: 'strncpy' specified
bound depends on the length o\
f the source argument [-Wstringop-truncation]
   65 |         strncpy(last_cmd, str, strlen(str) + 1);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../kernel/trace/trace_events_synth.c:65:32: note: length computed here
   65 |         strncpy(last_cmd, str, strlen(str) + 1);
      |                                ^~~~~~~~~~~

There's no reason to use strncpy here, in fact there's no reason to do
anything but a simple kstrdup() (note we don't even need to check for
failure since last_cmod is expected to be either the last cmd string
or NULL, and the containing function is a void return).

Fixes: 27c888da9867 ("tracing: Remove size restriction on synthetic
event cmd error logging")

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
---
 kernel/trace/trace_events_synth.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/trace/trace_events_synth.c
b/kernel/trace/trace_events_synth.c
index fdd79e07e2fc..5e8c07aef071 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -58,11 +58,8 @@ static void last_cmd_set(const char *str)
 		return;
 
 	kfree(last_cmd);
-	last_cmd = kzalloc(strlen(str) + 1, GFP_KERNEL);
-	if (!last_cmd)
-		return;
 
-	strncpy(last_cmd, str, strlen(str) + 1);
+	last_cmd = kstrdup(str, GFP_KERNEL);
 }
 
 static void synth_err(u8 err_type, u16 err_pos)
-- 
2.17.1