linux-kernel - Re: [PATCH v4 2/5] connector: use __get_task_comm in proc_comm

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Date:   Thu, 14 Oct 2021 09:48:09 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.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>,
        Benjamin Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        David Miller <davem@...emloft.net>, kuba@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Vladimir Zapolskiy <vzapolskiy@...il.com>,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH v4 2/5] connector: use __get_task_comm in proc_comm_connector

On Wed, Oct 13, 2021 at 10:19 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Wed, 13 Oct 2021 10:23:43 +0000
> Yafang Shao <laoar.shao@...il.com> wrote:
>
> > --- a/drivers/connector/cn_proc.c
> > +++ b/drivers/connector/cn_proc.c
> > @@ -230,7 +230,10 @@ 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 */
>
> __get_task_comm() uses strncpy() which my understanding is, does not add
> the nul terminating byte when truncating. Which changes the functionality
> here. As all task comms have a terminating byte, the old method would copy
> that and include it. This won't add the terminating byte if the buffer is
> smaller than the comm, and that might cause issues.
>

Right, that is a problem.
It seems that we should add a new helper get_task_comm_may_truncated().

-- 
Thanks
Yafang