linux-kernel - Re: [PATCH v6 02/12] fs/exec: make __get_task

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Date:   Tue, 26 Oct 2021 09:49:28 +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>,
        robdclark <robdclark@...omium.org>,
        christian <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>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        dennis.dalessandro@...nelisnetworks.com,
        mike.marciniszyn@...nelisnetworks.com, dledford@...hat.com,
        jgg@...pe.ca, linux-rdma@...r.kernel.org,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel test robot <oliver.sang@...el.com>,
        kbuild test robot <lkp@...el.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH v6 02/12] fs/exec: make __get_task_comm always get a nul
 terminated string

On Tue, Oct 26, 2021 at 5:08 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, Oct 25, 2021 at 08:33:05AM +0000, Yafang Shao wrote:
> > If the dest buffer size is smaller than sizeof(tsk->comm), the buffer
> > will be without null ternimator, that may cause problem. We can make sure
> > the buffer size not smaller than comm at the callsite to avoid that
> > problem, but there may be callsite that we can't easily change.
> >
> > Using strscpy_pad() instead of strncpy() in __get_task_comm() can make
> > the string always nul ternimated.
> >
> > Suggested-by: Kees Cook <keescook@...omium.org>
> > Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
> > Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Petr Mladek <pmladek@...e.com>
> > ---
> >  fs/exec.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/exec.c b/fs/exec.c
> > index 404156b5b314..bf2a7a91eeea 100644
> > --- a/fs/exec.c
> > +++ b/fs/exec.c
> > @@ -1209,7 +1209,8 @@ static int unshare_sighand(struct task_struct *me)
> >  char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk)
> >  {
> >       task_lock(tsk);
> > -     strncpy(buf, tsk->comm, buf_size);
> > +     /* The copied value is always null terminated */
>
> This may could say "always NUL terminated and zero-padded"
>

Sure. I will change it.

> > +     strscpy_pad(buf, tsk->comm, buf_size);
> >       task_unlock(tsk);
> >       return buf;
> >  }
> > --
> > 2.17.1
> >
>
> But for the replacement with strscpy_pad(), yes please:
>
> Reviewed-by: Kees Cook <keescook@...omium.org>
>
>
> --
> Kees Cook



-- 
Thanks
Yafang