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SubjectRe: [PATCH 4/7] fs/binfmt_elf: use get_task_comm instead of open-coded string copy
On Thu, Nov 11, 2021 at 7:47 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 11.11.21 12:34, Petr Mladek wrote:
> > On Thu 2021-11-11 11:06:04, David Hildenbrand wrote:
> >> On 11.11.21 11:03, David Hildenbrand wrote:
> >>> On 08.11.21 09:38, Yafang Shao wrote:
> >>>> It is better to use get_task_comm() instead of the open coded string
> >>>> copy as we do in other places.
> >>>>
> >>>> struct elf_prpsinfo is used to dump the task information in userspace
> >>>> coredump or kernel vmcore. Below is the verfication of vmcore,
> >>>>
> >>>> crash> ps
> >>>> PID PPID CPU TASK ST %MEM VSZ RSS COMM
> >>>> 0 0 0 ffffffff9d21a940 RU 0.0 0 0 [swapper/0]
> >>>>> 0 0 1 ffffa09e40f85e80 RU 0.0 0 0 [swapper/1]
> >>>>> 0 0 2 ffffa09e40f81f80 RU 0.0 0 0 [swapper/2]
> >>>>> 0 0 3 ffffa09e40f83f00 RU 0.0 0 0 [swapper/3]
> >>>>> 0 0 4 ffffa09e40f80000 RU 0.0 0 0 [swapper/4]
> >>>>> 0 0 5 ffffa09e40f89f80 RU 0.0 0 0 [swapper/5]
> >>>> 0 0 6 ffffa09e40f8bf00 RU 0.0 0 0 [swapper/6]
> >>>>> 0 0 7 ffffa09e40f88000 RU 0.0 0 0 [swapper/7]
> >>>>> 0 0 8 ffffa09e40f8de80 RU 0.0 0 0 [swapper/8]
> >>>>> 0 0 9 ffffa09e40f95e80 RU 0.0 0 0 [swapper/9]
> >>>>> 0 0 10 ffffa09e40f91f80 RU 0.0 0 0 [swapper/10]
> >>>>> 0 0 11 ffffa09e40f93f00 RU 0.0 0 0 [swapper/11]
> >>>>> 0 0 12 ffffa09e40f90000 RU 0.0 0 0 [swapper/12]
> >>>>> 0 0 13 ffffa09e40f9bf00 RU 0.0 0 0 [swapper/13]
> >>>>> 0 0 14 ffffa09e40f98000 RU 0.0 0 0 [swapper/14]
> >>>>> 0 0 15 ffffa09e40f9de80 RU 0.0 0 0 [swapper/15]
> >>>>
> >>>> It works well as expected.
> >>>>
> >>>> Suggested-by: Kees Cook <keescook@chromium.org>
> >>>> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> >>>> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> >>>> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
> >>>> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> >>>> Cc: Michal Miroslaw <mirq-linux@rere.qmqm.pl>
> >>>> Cc: Peter Zijlstra <peterz@infradead.org>
> >>>> Cc: Steven Rostedt <rostedt@goodmis.org>
> >>>> Cc: Matthew Wilcox <willy@infradead.org>
> >>>> Cc: David Hildenbrand <david@redhat.com>
> >>>> Cc: Al Viro <viro@zeniv.linux.org.uk>
> >>>> Cc: Kees Cook <keescook@chromium.org>
> >>>> Cc: Petr Mladek <pmladek@suse.com>
> >>>> ---
> >>>> fs/binfmt_elf.c | 2 +-
> >>>> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> >>>> index a813b70f594e..138956fd4a88 100644
> >>>> --- a/fs/binfmt_elf.c
> >>>> +++ b/fs/binfmt_elf.c
> >>>> @@ -1572,7 +1572,7 @@ static int fill_psinfo(struct elf_prpsinfo *psinfo, struct task_struct *p,
> >>>> SET_UID(psinfo->pr_uid, from_kuid_munged(cred->user_ns, cred->uid));
> >>>> SET_GID(psinfo->pr_gid, from_kgid_munged(cred->user_ns, cred->gid));
> >>>> rcu_read_unlock();
> >>>> - strncpy(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));
> >>>> + get_task_comm(psinfo->pr_fname, p);
> >>>>
> >>>> return 0;
> >>>> }
> >>>>
> >>>
> >>> We have a hard-coded "pr_fname[16]" as well, not sure if we want to
> >>> adjust that to use TASK_COMM_LEN?
> >>
> >> But if the intention is to chance TASK_COMM_LEN later, we might want to
> >> keep that unchanged.
> >
> > It seems that len will not change in the end. Another solution is
> > going to be used for the long names, see
> > https://lore.kernel.org/r/20211108084142.4692-1-laoar.shao@gmail.com.
>
> Yes, that's what I recall as well. The I read the patch
> subjects+descriptions in this series "make it adopt to task comm size
> change" and was slightly confused.
>
> Maybe we should just remove any notion of "task comm size change" from
> this series and instead just call it a cleanup.
>
>

Agreed that it may make a little confused for the one who didn't
engage in this series at the first place.
I will improve the subjection+description.


--
Thanks
Yafang

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