io_uring truncating coredumps

Eric W. Biederman
2022-01-17T18:47:01Z

Subject updated to reflect the current discussion.

> Linus Torvalds <torvalds@linux-foundation.org> writes:

> But I really think it's wrong.
>
> You're trying to work around a problem the wrong way around. If a task
> is dead, and is dumping core, then signals just shouldn't matter in
> the first place, and thus the whole "TASK_INTERRUPTIBLE vs
> TASK_UNINTERRUPTIBLE" really shouldn't be an issue. The fact that it
> is an issue means there's something wrong in signaling, not in the
> pipe code.
>
> So I really think that's where the fix should be - on the signal delivery side.

Thinking about it from the perspective of not delivering the wake-ups
fixing io_uring and coredumps in a non-hacky way looks comparatively
simple. The function task_work_add just needs to not wake anything up
after a process has started dying.

Something like the patch below.

The only tricky part I can see is making certain there are not any races
between task_work_add and do_coredump depending on task_work_add not
causing signal_pending to return true.

diff --git a/kernel/task_work.c b/kernel/task_work.c
index fad745c59234..5f941e377268 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -44,6 +44,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
work->next = head;
} while (cmpxchg(&task->task_works, head, work) != head);

+ if (notify && (task->signal->flags & SIGNAL_GROUP_EXIT))
+ return 0;
+
switch (notify) {
case TWA_NONE:
break;

Eric