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

From: Yafang Shao <laoar.shao@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	netdev <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	"linux-perf-use." <linux-perf-users@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org, Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel test robot <oliver.sang@intel.com>,
	kbuild test robot <lkp@intel.com>,
	Kees Cook <keescook@chromium.org>,
	David Hildenbrand <david@redhat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
	Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Michal Miroslaw <mirq-linux@rere.qmqm.pl>,
	Peter Zijlstra <peterz@infradead.org>,
	Matthew Wilcox <willy@infradead.org>,
	Al Viro <viro@zeniv.linux.org.uk>, Petr Mladek <pmladek@suse.com>
Subject: Re: [PATCH v2 4/7] fs/binfmt_elf: replace open-coded string copy with get_task_comm
Date: Tue, 30 Nov 2021 11:01:27 +0800	[thread overview]
Message-ID: <CALOAHbB-2ESG0QgESN_b=bXzESbq+UBP-dqttirKnt1c9TZHZA@mail.gmail.com> (raw)
In-Reply-To: <20211129110140.733475f3@gandalf.local.home>

On Tue, Nov 30, 2021 at 12:01 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Sat, 20 Nov 2021 11:27:35 +0000
> Yafang Shao <laoar.shao@gmail.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