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SubjectRe: [PATCH v7 7/9] seccomp: implement SECCOMP_FILTER_FLAG_TSYNC
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(&current->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) {
> + pid_t failed;
> +
> + if (thread->seccomp.mode == SECCOMP_MODE_DISABLED ||
> + (thread->seccomp.mode == SECCOMP_MODE_FILTER &&
> + is_ancestor(thread->seccomp.filter,
> + caller->seccomp.filter)))
> + continue;
> +
> + /* Return the first thread that cannot be synchronized. */
> + failed = task_pid_vnr(thread);
> + /* If the pid cannot be resolved, then return -ESRCH */
> + if (failed == 0)
> + failed = -ESRCH;

forgot to mention, task_pid_vnr() can't fail. sighand->siglock is held,
for_each_thread() can't see a thread which has passed unhash_process().

Oleg.



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