On Thu, Nov 11, 2021 at 7:35 PM Petr Mladek [off-list ref] wrote:

On Thu 2021-11-11 11:06:04, David Hildenbrand wrote:

quoted

On 11.11.21 11:03, David Hildenbrand wrote:

quoted

On 08.11.21 09:38, Yafang Shao wrote:

quoted

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]

quoted

    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]

quoted

    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 <redacted>
Signed-off-by: Yafang Shao <redacted>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Arnaldo Carvalho de Melo <redacted>
Cc: Andrii Nakryiko <redacted>
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 <redacted>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <redacted>
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 (local).

quoted

(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)

If the code would need some tweaking when the size changes, you could
still use TASK_COMM_LEN and trigger a compilation error when the size
gets modified. For example, static_assert(TASK_COMM_LEN == 16);

It will make it clear that it needs attention if the size is ever modified.

I think we can just add some comments to make it grepable, for example,

+  /* TASK_COMM_LEN */
    char pr_fname[16];

or a more detailed explanation:

+  /*
+   * The hard-coded 16 is derived from TASK_COMM_LEN, but it can be changed as
+   *  it is exposed to userspace. We'd better make it hard-coded here.
+   */
char pr_fname[16];

-- 
Thanks
Yafang