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

[David Hildenbrand <david@redhat.com>]

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?

Anyhow

Reviewed-by: David Hildenbrand <david@redhat.com>


-- 
Thanks,

David / dhildenb