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

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 10 Mar 2022 10:45:09 -0600
Tom Zanussi <zanussi@kernel.org> wrote:

> 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:

Can you send this as a normal patch. My scripts do not pick up patches as
replies (besides patch series) or embedded in other email threads.

-- Steve


> 
> ../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)