On Wed, Nov 10, 2021 at 4:28 PM David Hildenbrand [off-list ref] wrote:

On 08.11.21 09:38, Yafang Shao wrote:

quoted

Make sure the string set to task comm is always nul terminated.

strlcpy: "the result is always a valid NUL-terminated string that fits
in the buffer"

The only difference seems to be that strscpy_pad() pads the remainder
with zeroes.

Is this description correct and I am missing something important?

In a earlier version [1], the checkpatch.py found a warning:
WARNING: Prefer strscpy over strlcpy - see:
https://lore.kernel.org/r/CAHk-=wgfRnXz0W3D37d01q3JFkr_i_uTL=V6A6G1oUZcprmknw@mail.gmail.com/ (local)
So I replaced strlcpy() with strscpy() to fix this warning.
And then in v5[2], the strscpy() was replaced with strscpy_pad() to
make sure there's no garbade data and also make get_task_comm() be
consistent with get_task_comm().

This commit log didn't clearly describe the historical changes.  So I
think we can update the commit log and subject with:

Subject: use strscpy_pad with strlcpy in __set_task_comm
Commit log:
strlcpy is not suggested to use by the checkpatch.pl, so we'd better
recplace it with strscpy.
To avoid leaving garbage data and be consistent with the usage in
__get_task_comm(), the strscpy_pad is used here.

WDYT?

[1]. https://lore.kernel.org/lkml/20211007120752.5195-3-laoar.shao@gmail.com/ (local)
[2]. https://lore.kernel.org/lkml/20211021034516.4400-2-laoar.shao@gmail.com/ (local)

quoted

Signed-off-by: Yafang Shao <redacted>
Reviewed-by: Kees Cook <redacted>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Arnaldo Carvalho de Melo <redacted>
Cc: Alexei Starovoitov <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/exec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index a098c133d8d7..404156b5b314 100644
--- a/fs/exec.c
+++ b/fs/exec.c

@@ -1224,7 +1224,7 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
 {
      task_lock(tsk);
      trace_task_rename(tsk, buf);
-     strlcpy(tsk->comm, buf, sizeof(tsk->comm));
+     strscpy_pad(tsk->comm, buf, sizeof(tsk->comm));
      task_unlock(tsk);
      perf_event_comm(tsk, exec);
 }

--
Thanks,

David / dhildenb

-- 
Thanks
Yafang