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 Wed, 2022-03-09 at 23:48 +0800, kernel test robot wrote:
> Hi Tom,
> 
> FYI, the error/warning still remains.
> 
> 

Thanks, the patch below fixes it.  I'll submit to lkml, but not sure
whether to submit the fix or resubmit the original patch...

Tom


[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, since the buffer being copied
to was just allocated as strlen(str) + 1, and therefore the strcpy()
of str will exactly fit, including the null terminator.

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 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index fdd79e07e2fc..a133396ee29d 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -62,7 +62,7 @@ static void last_cmd_set(const char *str)
 	if (!last_cmd)
 		return;
 
-	strncpy(last_cmd, str, strlen(str) + 1);
+	strcpy(last_cmd, str);
 }
 
 static void synth_err(u8 err_type, u16 err_pos)
-- 
2.17.1