Re: [PATCH] coredump: Do not lock during 'comm' reporting

[Kees Cook <kees@kernel.org>]

On Sat, Sep 28, 2024 at 02:46:36PM -0700, Andrew Morton wrote:
> On Sat, 28 Sep 2024 14:39:45 -0700 Kees Cook <kees@kernel.org> wrote:
> 
> > On Sat, Sep 28, 2024 at 02:35:32PM -0700, Andrew Morton wrote:
> > > On Sat, 28 Sep 2024 14:08:31 -0700 Kees Cook <kees@kernel.org> wrote:
> > > 
> > > > The 'comm' member will always be NUL terminated,
> > > 
> > > Why is this?  I thought this is only true if the caller holds task_lock()?
> > 
> > Because it's always written with strscpy_pad(). The final byte will
> > always be NUL. (And this has been true for a very long time.)
> 
> So why does __get_task_comm() need to take task_lock()?

That was to make sure we didn't end up with garbled results, but
discussions have determined that we don't care:
https://lore.kernel.org/all/20240828030321.20688-1-laoar.shao@gmail.com/

But just for safety's sake, I'll change this memcpy to:

    memcpy_and_pad(comm, sizeof(comm), current->comm, sizeof(comm) - 1, 0);

-- 
Kees Cook