Re: [PATCH 3/5] kernel/sched: improve the BUILD_BUG_ON() in get_task_comm()

[Kees Cook <keescook@chromium.org>]

On Wed, Sep 29, 2021 at 11:50:34AM +0000, Yafang Shao wrote:
> What we really want to guarantee is that the buf size can't be less than
> TASK_COMM_LEN. While the size be greater than TASK_COMM_LEN is
> acceptable.

This makes sense when task_struct::comm is a pointer. (But I think it's
not a good idea to do that.)

-Kees

> 
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
>  include/linux/sched.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index b387b5943db4..959eaef248fc 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1931,7 +1931,7 @@ static inline void set_task_comm(struct task_struct *tsk, const char *from)
>  
>  extern char *__get_task_comm(char *to, size_t len, struct task_struct *tsk);
>  #define get_task_comm(buf, tsk) ({			\
> -	BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN);	\
> +	BUILD_BUG_ON(sizeof(buf) < TASK_COMM_LEN);	\
>  	__get_task_comm(buf, sizeof(buf), tsk);		\
>  })
>  
> -- 
> 2.17.1
> 

-- 
Kees Cook