Re: [PATCH v2 2/5] exec: Factor unshare_sighand out of de_thread and call it separately

Kees Cook
2020-03-10T20:57:59Z

On Tue, Mar 10, 2020 at 09:34:03PM +0100, Bernd Edlinger wrote:
> On 3/10/20 9:29 PM, Kees Cook wrote:
> > On Sun, Mar 08, 2020 at 04:36:17PM -0500, Eric W. Biederman wrote:
> >>
> >> This makes the code clearer and makes it easier to implement a mutex
> >> that is not taken over any locations that may block indefinitely waiting
> >> for userspace.
> >>
> >> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> >> ---
> >> fs/exec.c | 39 ++++++++++++++++++++++++++-------------
> >> 1 file changed, 26 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/fs/exec.c b/fs/exec.c
> >> index c3f34791f2f0..ff74b9a74d34 100644
> >> --- a/fs/exec.c
> >> +++ b/fs/exec.c
> >> @@ -1194,6 +1194,23 @@ static int de_thread(struct task_struct *tsk)
> >> flush_itimer_signals();
> >> #endif
> >
> > Semi-related (existing behavior): in de_thread(), what keeps the thread
> > group from changing? i.e.:
> >
> > if (thread_group_empty(tsk))
> > goto no_thread_group;
> >
> > /*
> > * Kill all other threads in the thread group.
> > */
> > spin_lock_irq(lock);
> > ... kill other threads under lock ...
> >
> > Why is the thread_group_emtpy() test not under lock?
> >
>
> A new thread cannot created when only one thread is executing,
> right?

*face palm* Yes, of course. :) I'm thinking too hard.

--
Kees Cook