Re: [PATCH v5 0/9] Improve the copy of task comm

[Yafang Shao <laoar.shao@gmail.com>]

On Tue, Aug 6, 2024 at 11:10 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Mon, 5 Aug 2024 at 20:01, Yafang Shao <laoar.shao@gmail.com> wrote:
> >
> > One concern about removing the BUILD_BUG_ON() is that if we extend
> > TASK_COMM_LEN to a larger size, such as 24, the caller with a
> > hardcoded 16-byte buffer may overflow.
>
> No, not at all. Because get_task_comm() - and the replacements - would
> never use TASK_COMM_LEN.
>
> They'd use the size of the *destination*. That's what the code already does:
>
>   #define get_task_comm(buf, tsk) ({                      \
>   ...
>         __get_task_comm(buf, sizeof(buf), tsk);         \
>
> note how it uses "sizeof(buf)".
>
> Now, it might be a good idea to also verify that 'buf' is an actual
> array, and that this code doesn't do some silly "sizeof(ptr)" thing.
>
> We do have a helper for that, so we could do something like
>
>    #define get_task_comm(buf, tsk) \
>         strscpy_pad(buf, __must_be_array(buf)+sizeof(buf), (tsk)->comm)
>
> as a helper macro for this all.
>
> (Although I'm not convinced we generally want the "_pad()" version,
> but whatever).
>

Will do it.
Thanks for your explanation.

-- 
Regards
Yafang