Re: [PATCH 1/2] signal: don't allow sending any signals to PF_IO_WORKER threads

Eric W. Biederman
2021-03-20T16:20:44Z

Jens Axboe <axboe@kernel.dk> writes:

> They don't take signals individually, and even if they share signals with
> the parent task, don't allow them to be delivered through the worker
> thread.

This is silly I know, but why do we care?

The creds should be reasonably in-sync with the rest of the threads.

There are other threads that will receive the signal, especially when
you worry about group_send_sig_info. Which signal sending code paths
are actually a problem.

> Reported-by: Stefan Metzmacher <metze@samba.org>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
> kernel/signal.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index ba4d1ef39a9e..730ecd3d6faf 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -833,6 +833,9 @@ static int check_kill_permission(int sig, struct kernel_siginfo *info,
>
> if (!valid_signal(sig))
> return -EINVAL;
> + /* PF_IO_WORKER threads don't take any signals */
> + if (t->flags & PF_IO_WORKER)
> + return -EPERM;
>
> if (!si_fromuser(info))
> return 0;