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

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Message-ID: <CALOAHbANTC8vQ+f4q_YzFtYtd5Ffrm_nx8Y42552X1kXTCCS7Q@mail.gmail.com>
Date:   Thu, 30 Sep 2021 20:43:43 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        qiang.zhang@...driver.com, robdclark@...omium.org,
        Al Viro <viro@...iv.linux.org.uk>, christian@...uner.io,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] kernel/sched: improve the BUILD_BUG_ON() in get_task_comm()

On Thu, Sep 30, 2021 at 2:12 AM Kees Cook <keescook@...omium.org> wrote:
>
> 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.)
>

OK, I won't make this change.

> >
> > Signed-off-by: Yafang Shao <laoar.shao@...il.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



-- 
Thanks
Yafang