Re: [PATCH 4/7] fs/binfmt_elf: use get_task_comm instead of open-coded string copy

[Yafang Shao]

On Thu, Nov 11, 2021 at 7:47 PM David Hildenbrand <david@xxxxxxxxxx> 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@xxxxxxxxxxxx>
> >>>> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> >>>> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> >>>> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
> >>>> Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> >>>> Cc: Michal Miroslaw <mirq-linux@xxxxxxxxxxxx>
> >>>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> >>>> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> >>>> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> >>>> Cc: David Hildenbrand <david@xxxxxxxxxx>
> >>>> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> >>>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> >>>> Cc: Petr Mladek <pmladek@xxxxxxxx>
> >>>> ---
> >>>>  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@xxxxxxxxx.
>
> 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