Re: [PATCH v2 13/18] rtla: Fix buffer size for strncpy in timerlat_aa

[Steven Rostedt <rostedt@goodmis.org>]

On Tue,  6 Jan 2026 08:49:49 -0300
Wander Lairson Costa <wander@redhat.com> wrote:

> The run_thread_comm and current_comm character arrays in struct
> timerlat_aa_data are defined with size MAX_COMM (24 bytes), but
> strncpy() is called with MAX_COMM as the size parameter. If the
> source string is exactly MAX_COMM bytes or longer, strncpy() will
> copy exactly MAX_COMM bytes without null termination, potentially
> causing buffer overruns when these strings are later used.

We should implement something like the kernel has of "strscpy()" which not
only truncates but also adds a null terminating byte.

> 
> Increase the buffer sizes to MAX_COMM+1 to ensure there is always
> room for the null terminator. This guarantees that even when strncpy()
> copies the maximum number of characters, the buffer remains properly
> null-terminated and safe to use in subsequent string operations.
> 
> Signed-off-by: Wander Lairson Costa <wander@redhat.com>
> ---
>  tools/tracing/rtla/src/timerlat_aa.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/tracing/rtla/src/timerlat_aa.c b/tools/tracing/rtla/src/timerlat_aa.c
> index 31e66ea2b144c..d310fe65abace 100644
> --- a/tools/tracing/rtla/src/timerlat_aa.c
> +++ b/tools/tracing/rtla/src/timerlat_aa.c
> @@ -47,7 +47,7 @@ struct timerlat_aa_data {
>  	 * note: "unsigned long long" because they are fetch using tep_get_field_val();
>  	 */
>  	unsigned long long	run_thread_pid;
> -	char			run_thread_comm[MAX_COMM];
> +	char			run_thread_comm[MAX_COMM+1];

The reason why I suggest strscpy() is because now you just made every this
unaligned in the struct. 24 bytes fits nicely as 3 8 byte words. Now by
adding another byte, you just added 7 bytes of useless padding between this
and the next field.

-- Steve


>  	unsigned long long	thread_blocking_duration;
>  	unsigned long long	max_exit_idle_latency;
>  
> @@ -88,7 +88,7 @@ struct timerlat_aa_data {
>  	/*
>  	 * Current thread.
>  	 */
> -	char			current_comm[MAX_COMM];
> +	char			current_comm[MAX_COMM+1];
>  	unsigned long long	current_pid;
>  
>  	/*