[PATCH] tracing: avoid string overflow

[PATCH] tracing: avoid string overflow

[Arnd Bergmann]

'err' is used as a NUL-terminated string, but using strncpy() with the length
equal to the buffer size may result in lack of the termination:

kernel/trace/trace_events_hist.c: In function 'hist_err_event':
kernel/trace/trace_events_hist.c:396:3: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
   strncpy(err, var, MAX_FILTER_STR_VAL);

This changes it to use the safer strscpy() instead.

Fixes: f404da6e1d46 ("tracing: Add 'last error' error facility for hist triggers")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 kernel/trace/trace_events_hist.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 4f027642ceef..8357f36d7a1e 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -393,7 +393,7 @@ static void hist_err_event(char *str, char *system, char *event, char *var)
 	else if (system)
 		snprintf(err, MAX_FILTER_STR_VAL, "%s.%s", system, event);
 	else
-		strncpy(err, var, MAX_FILTER_STR_VAL);
+		strscpy(err, var, MAX_FILTER_STR_VAL);
 
 	hist_err(str, err);
 }
-- 
2.9.0

Re: [PATCH] tracing: avoid string overflow

[Tom Zanussi]

Hi Arnd,

On Wed, 2018-03-28 at 16:09 +0200, Arnd Bergmann wrote:
> 'err' is used as a NUL-terminated string, but using strncpy() with the length
> equal to the buffer size may result in lack of the termination:
> 
> kernel/trace/trace_events_hist.c: In function 'hist_err_event':
> kernel/trace/trace_events_hist.c:396:3: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
>    strncpy(err, var, MAX_FILTER_STR_VAL);
> 
> This changes it to use the safer strscpy() instead.
> 
> Fixes: f404da6e1d46 ("tracing: Add 'last error' error facility for hist triggers")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  kernel/trace/trace_events_hist.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 4f027642ceef..8357f36d7a1e 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -393,7 +393,7 @@ static void hist_err_event(char *str, char *system, char *event, char *var)
>  	else if (system)
>  		snprintf(err, MAX_FILTER_STR_VAL, "%s.%s", system, event);
>  	else
> -		strncpy(err, var, MAX_FILTER_STR_VAL);
> +		strscpy(err, var, MAX_FILTER_STR_VAL);
>  
>  	hist_err(str, err);
>  }

Yes, thanks for finding this, and for the patch! 

Acked-by: Tom Zanussi <tom.zanussi@linux.intel.com>

Re: [PATCH] tracing: avoid string overflow

[Steven Rostedt]

On Wed, 28 Mar 2018 16:09:10 +0200
Arnd Bergmann <arnd@arndb.de> wrote:

> 'err' is used as a NUL-terminated string, but using strncpy() with the length
> equal to the buffer size may result in lack of the termination:
> 
> kernel/trace/trace_events_hist.c: In function 'hist_err_event':
> kernel/trace/trace_events_hist.c:396:3: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
>    strncpy(err, var, MAX_FILTER_STR_VAL);
> 
> This changes it to use the safer strscpy() instead.
> 
> Fixes: f404da6e1d46 ("tracing: Add 'last error' error facility for hist triggers")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks! I pulled this in and will push it to git after testing has
succeeded.

-- Steve

> ---
>  kernel/trace/trace_events_hist.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 4f027642ceef..8357f36d7a1e 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -393,7 +393,7 @@ static void hist_err_event(char *str, char *system, char *event, char *var)
>  	else if (system)
>  		snprintf(err, MAX_FILTER_STR_VAL, "%s.%s", system, event);
>  	else
> -		strncpy(err, var, MAX_FILTER_STR_VAL);
> +		strscpy(err, var, MAX_FILTER_STR_VAL);
>  
>  	hist_err(str, err);
>  }