linux-kernel - Re: [PATCH v2 1/4] cn_proc.h: use TASK_COMM_LEN instread of 16 in struct proc

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Date:   Thu, 7 Oct 2021 23:45:08 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Petr Mladek <pmladek@...e.com>, Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        qiang.zhang@...driver.com, robdclark@...omium.org,
        christian@...uner.io, Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Vladimir Zapolskiy <vzapolskiy@...il.com>
Subject: Re: [PATCH v2 1/4] cn_proc.h: use TASK_COMM_LEN instread of 16 in
 struct proc_event

On Thu, Oct 7, 2021 at 11:09 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, Oct 07, 2021 at 07:51:35AM -0700, Kees Cook wrote:
> > On Thu, Oct 07, 2021 at 12:07:49PM +0000, Yafang Shao wrote:
> > > struct comm_proc_event was introduced in commit
> > > f786ecba4158 ("connector: add comm change event report to proc connector").
> > > It seems that there is no strong reason we must define the comm as a
> > > hardcode 16 bytes. So we can use TASK_COMM_LEN instead.
> > >
> > > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > > Cc: Vladimir Zapolskiy <vzapolskiy@...il.com>
> > > Cc: Kees Cook <keescook@...omium.org>
> > > Cc: Al Viro <viro@...iv.linux.org.uk>
> > > Cc: Petr Mladek <pmladek@...e.com>
> > > ---
> > >  include/uapi/linux/cn_proc.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/uapi/linux/cn_proc.h b/include/uapi/linux/cn_proc.h
> > > index db210625cee8..351d02786350 100644
> > > --- a/include/uapi/linux/cn_proc.h
> > > +++ b/include/uapi/linux/cn_proc.h
> > > @@ -110,7 +110,7 @@ struct proc_event {
> > >             struct comm_proc_event {
> > >                     __kernel_pid_t process_pid;
> > >                     __kernel_pid_t process_tgid;
> > > -                   char           comm[16];
> > > +                   char           comm[TASK_COMM_LEN];
> > >             } comm;
> >
> > Hrmm. This is UAPI -- 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). This will either need to stay truncated, or may
> > need a new interface with a variable-sized structure...
>
> Specifically, this is needed for this series:
>
>
> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
> index 646ad385e490..34bcba25c488 100644
> --- a/drivers/connector/cn_proc.c
> +++ b/drivers/connector/cn_proc.c
> @@ -230,7 +230,9 @@ void proc_comm_connector(struct task_struct *task)
>         ev->what = PROC_EVENT_COMM;
>         ev->event_data.comm.process_pid  = task->pid;
>         ev->event_data.comm.process_tgid = task->tgid;
> -       get_task_comm(ev->event_data.comm.comm, task);
> +       /* This may get truncated. */
> +       __get_task_comm(ev->event_data.comm.comm,
> +                       sizeof(ev->event_data.comm.comm), task);
>
>         memcpy(&msg->id, &cn_proc_event_id, sizeof(msg->id));
>         msg->ack = 0; /* not used */
>

Thanks for the suggestion.  I will keep the UAPI code as-is and change
it as you suggested.

-- 
Thanks
Yafang