linux-kernel - Re: [PATCH v6 03/12] drivers/connector: make connector comm always nul ternimated

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Message-ID: <CALOAHbBwRcZoRteU7qL7rdip=cbTHc3n6-eJrd6xUoeJ+Win6Q@mail.gmail.com>
Date:   Tue, 26 Oct 2021 09:50:43 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Valentin Schneider <valentin.schneider@....com>,
        Qiang Zhang <qiang.zhang@...driver.com>,
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Subject: Re: [PATCH v6 03/12] drivers/connector: make connector comm always
 nul ternimated

On Tue, Oct 26, 2021 at 5:14 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, Oct 25, 2021 at 08:33:06AM +0000, Yafang Shao wrote:
> > connector comm was introduced in commit
> > f786ecba4158 ("connector: add comm change event report to proc connector").
> > struct comm_proc_event was defined in include/linux/cn_proc.h first and
> > then been moved into file include/uapi/linux/cn_proc.h in commit
> > 607ca46e97a1 ("UAPI: (Scripted) Disintegrate include/linux").
> >
> > As this is the UAPI code, we can't change it without potentially breaking
> > things (i.e. userspace binaries have this size built in, so we can't just
> > change the size). To prepare for the followup change - extending task
> > comm, we have to use __get_task_comm() to avoid the BUILD_BUG_ON() in
> > proc_comm_connector().
>
> I wonder, looking at this again, if it might make more sense to avoid
> this cn_proc.c change, and instead, adjust get_task_comm() like so:
>
> #define get_task_comm(buf, tsk)
>         __get_task_comm(buf, __must_be_array(buf) + sizeof(buf), tsk)
>
> This would still enforce the original goal of making sure
> get_task_comm() is being used on a char array, and now that
> __get_task_comm() will truncate & pad, it's safe to use on both
> too-small and too-big arrays.
>

It Makes sense to me.  I will do it as you suggested.

-- 
Thanks
Yafang