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

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Date:   Thu, 11 Nov 2021 11:06:04 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Yafang Shao <laoar.shao@...il.com>, akpm@...ux-foundation.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        oliver.sang@...el.com, lkp@...el.com,
        Kees Cook <keescook@...omium.org>,
        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>,
        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 4/7] fs/binfmt_elf: use get_task_comm instead of
 open-coded string copy

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@...omium.org>
>> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
>> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...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/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.

(replacing the 16 by a define might still be a good idea, similar to how
it's done for ELF_PRARGSZ, but just a thought)


-- 
Thanks,

David / dhildenb