netdev - Re: [PATCH v2 4/7] fs/binfmt_elf: replace open-coded string copy with get_task

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Date:   Tue, 30 Nov 2021 11:01:27 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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>,
        David Hildenbrand <david@...hat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Michal Miroslaw <mirq-linux@...e.qmqm.pl>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH v2 4/7] fs/binfmt_elf: replace open-coded string copy with get_task_comm

On Tue, Nov 30, 2021 at 12:01 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Sat, 20 Nov 2021 11:27:35 +0000
> Yafang Shao <laoar.shao@...il.com> wrote:
>
> > diff --git a/include/linux/elfcore-compat.h b/include/linux/elfcore-compat.h
> > index e272c3d452ce..54feb64e9b5d 100644
> > --- a/include/linux/elfcore-compat.h
> > +++ b/include/linux/elfcore-compat.h
> > @@ -43,6 +43,11 @@ struct compat_elf_prpsinfo
> >       __compat_uid_t                  pr_uid;
> >       __compat_gid_t                  pr_gid;
> >       compat_pid_t                    pr_pid, pr_ppid, pr_pgrp, pr_sid;
> > +     /*
> > +      * The hard-coded 16 is derived from TASK_COMM_LEN, but it can't be
> > +      * changed as it is exposed to userspace. We'd better make it hard-coded
> > +      * here.
>
> Didn't I once suggest having a macro called something like:
>
>   TASK_COMM_LEN_16 ?
>
>
> https://lore.kernel.org/all/20211014221409.5da58a42@oasis.local.home/

Hi Steven,

TASK_COMM_LEN_16 is a good idea, but not all hard-coded 16 can be
replaced by this macro (which is defined in include/sched.h).
For example,  the comm[16] in include/uapi/linux/cn_proc.h can't be
replaced as it is a uapi header which can't include  linux/sched.h.
That's why I prefer to keep the hard-coded 16 as-is.

There are three options,
- option 1
  comment on all the hard-coded 16 to explain why it is hard-coded
- option 2
  replace the hard-coded 16 that can be replaced and comment on the
others which can't be replaced.
- option 3
   replace the hard-coded 16 that can be replaced and specifically
define TASK_COMM_LEN_16 in other files which can't include
linux/sched.h.

Which one do you prefer ?


>
>
> > +      */
> >       char                            pr_fname[16];
> >       char                            pr_psargs[ELF_PRARGSZ];
> >  };
> > diff --git a/include/linux/elfcore.h b/include/linux/elfcore.h
> > index 957ebec35aad..746e081879a5 100644
> > --- a/include/linux/elfcore.h
> > +++ b/include/linux/elfcore.h
> > @@ -65,6 +65,11 @@ struct elf_prpsinfo
> >       __kernel_gid_t  pr_gid;
> >       pid_t   pr_pid, pr_ppid, pr_pgrp, pr_sid;
> >       /* Lots missing */
> > +     /*
> > +      * The hard-coded 16 is derived from TASK_COMM_LEN, but it can't be
> > +      * changed as it is exposed to userspace. We'd better make it hard-coded
> > +      * here.
> > +      */
> >       char    pr_fname[16];   /* filename of executable */
> >       char    pr_psargs[ELF_PRARGSZ]; /* initial part of arg list */
> >  };



-- 
Thanks
Yafang