On 06/23, Kees Cook wrote:
>
> +static pid_t seccomp_can_sync_threads(void)
> +{
> + struct task_struct *thread, *caller;
> +
> + BUG_ON(write_can_lock(&tasklist_lock));
> + BUG_ON(!spin_is_locked(¤t->sighand->siglock));
> +
> + if (current->seccomp.mode != SECCOMP_MODE_FILTER)
> + return -EACCES;
> +
> + /* Validate all threads being eligible for synchronization. */
> + thread = caller = current;
> + for_each_thread(caller, thread) {
You only need to initialize "caller" for for_each_thread(). Same for
seccomp_sync_threads().
> @@ -586,6 +701,17 @@ static long seccomp_set_mode_filter(unsigned int flags,
> if (IS_ERR(prepared))
> return PTR_ERR(prepared);
>
> + /*
> + * If we're doing thread sync, we must hold tasklist_lock
> + * to make sure seccomp filter changes are stable on threads
> + * entering or leaving the task list. And we must take it
> + * before the sighand lock to avoid deadlocking.
> + */
> + if (flags & SECCOMP_FILTER_FLAG_TSYNC)
> + write_lock_irqsave(&tasklist_lock, taskflags);
> + else
> + __acquire(&tasklist_lock); /* keep sparse happy */
> +
Why? ->siglock should be enough, it seems.
It obviously does not protect the global process list, but *sync_threads()
only care about current's thread group list, no?
Oleg.
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