linux-kernel - Re: [PATCH 1/7] fs/exec: make __set_task_comm always set a nul terminated string

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Date:   Wed, 10 Nov 2021 17:05:44 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.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>,
        Kees Cook <keescook@...omium.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Michal Miroslaw <mirq-linux@...e.qmqm.pl>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH 1/7] fs/exec: make __set_task_comm always set a nul
 terminated string

On Wed, Nov 10, 2021 at 4:28 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 08.11.21 09:38, Yafang Shao wrote:
> > Make sure the string set to task comm is always nul terminated.
> >
>
> strlcpy: "the result is always a valid NUL-terminated string that fits
> in the buffer"
>
> The only difference seems to be that strscpy_pad() pads the remainder
> with zeroes.
>
> Is this description correct and I am missing something important?
>

In a earlier version [1], the checkpatch.py found a warning:
WARNING: Prefer strscpy over strlcpy - see:
https://lore.kernel.org/r/CAHk-=wgfRnXz0W3D37d01q3JFkr_i_uTL=V6A6G1oUZcprmknw@mail.gmail.com/
So I replaced strlcpy() with strscpy() to fix this warning.
And then in v5[2], the strscpy() was replaced with strscpy_pad() to
make sure there's no garbade data and also make get_task_comm() be
consistent with get_task_comm().

This commit log didn't clearly describe the historical changes.  So I
think we can update the commit log and subject with:

Subject: use strscpy_pad with strlcpy in __set_task_comm
Commit log:
strlcpy is not suggested to use by the checkpatch.pl, so we'd better
recplace it with strscpy.
To avoid leaving garbage data and be consistent with the usage in
__get_task_comm(), the strscpy_pad is used here.

WDYT?

[1]. https://lore.kernel.org/lkml/20211007120752.5195-3-laoar.shao@gmail.com/
[2]. https://lore.kernel.org/lkml/20211021034516.4400-2-laoar.shao@gmail.com/

> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
> > Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
> > Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> > Cc: Michal Miroslaw <mirq-linux@...e.qmqm.pl>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Matthew Wilcox <willy@...radead.org>
> > Cc: David Hildenbrand <david@...hat.com>
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Petr Mladek <pmladek@...e.com>
> > ---
> >  fs/exec.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/exec.c b/fs/exec.c
> > index a098c133d8d7..404156b5b314 100644
> > --- a/fs/exec.c
> > +++ b/fs/exec.c
> > @@ -1224,7 +1224,7 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
> >  {
> >       task_lock(tsk);
> >       trace_task_rename(tsk, buf);
> > -     strlcpy(tsk->comm, buf, sizeof(tsk->comm));
> > +     strscpy_pad(tsk->comm, buf, sizeof(tsk->comm));
> >       task_unlock(tsk);
> >       perf_event_comm(tsk, exec);
> >  }
> >
>
>
> --
> Thanks,
>
> David / dhildenb
>


-- 
Thanks
Yafang