Hi!
> +SYSCALL_DEFINE5(pidctl, unsigned int, cmd, pid_t, pid, int, source, int,
> target,
> + unsigned int, flags)
> +{
> + struct pid_namespace *source_ns = NULL, *target_ns = NULL;
> + struct pid *struct_pid;
> + pid_t result;
> +
> + switch (cmd) {
> + case PIDCMD_QUERY_PIDNS:
> + if (pid != 0)
> + return -EINVAL;
> + pid = 1;
> + /* fall through */
> + case PIDCMD_QUERY_PID:
> + if (flags != 0)
> + return -EINVAL;
> + break;
> + case PIDCMD_GET_PIDFD:
> + if (flags & ~PIDCTL_CLOEXEC)
> + return -EINVAL;
> + break;
> + default:
> + return -EOPNOTSUPP;
> + }
> +
> + source_ns = get_pid_ns_by_fd(source);
> + result = PTR_ERR(source_ns);
> + if (IS_ERR(source_ns))
> + goto err_source;
> +
> + target_ns = get_pid_ns_by_fd(target);
> + result = PTR_ERR(target_ns);
> + if (IS_ERR(target_ns))
> + goto err_target;
> +
> + if (cmd == PIDCMD_QUERY_PIDNS) {
> + result = pidns_related(source_ns, target_ns);
> + } else {
> + rcu_read_lock();
> + struct_pid = find_pid_ns(pid, source_ns);
> + result = struct_pid ? pid_nr_ns(struct_pid, target_ns) : -ESRCH;
Should you do get_pid(struct_pid) here to keep it alive till
pidfd_create_fd() ?
> + rcu_read_unlock();
> +
> + if (cmd == PIDCMD_GET_PIDFD) {
> + int cloexec = (flags & PIDCTL_CLOEXEC) ? O_CLOEXEC : 0;
> + if (result > 0)
> + result = pidfd_create_fd(struct_pid, cloexec);
> + else if (result == 0)
> + result = -ENOENT;
> + }
> + }
> +
> + if (target)
> + put_pid_ns(target_ns);
> +err_target:
> + if (source)
> + put_pid_ns(source_ns);
> +err_source:
> + return result;
> +}
> +
> void __init pid_idr_init(void)
> {
> /* Verify no one has done anything silly: */
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index aa6e72fb7c08..1c863fb3d55a 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -429,6 +429,31 @@ static struct ns_common *pidns_get_parent(struct
> ns_common *ns)
> return &get_pid_ns(pid_ns)->ns;
> }
>
> +/**
> + * pidnscmp - Determine if @ancestor is ancestor of @descendant
> + * @ancestor: pidns suspected to be the ancestor of @descendant
> + * @descendant: pidns suspected to be the descendant of @ancestor
> + *
> + * Returns -1 if @ancestor is not an ancestor of @descendant,
> + * 0 if @ancestor is the same pidns as @descendant, 1 if @ancestor
> + * is an ancestor of @descendant.
> + */
> +int pidnscmp(struct pid_namespace *ancestor, struct pid_namespace
> *descendant)
> +{
> + if (ancestor == descendant)
> + return 0;
> +
> + for (;;) {
> + if (!descendant)
> + return -1;
> + if (descendant == ancestor)
> + break;
> + descendant = descendant->parent;
> + }
> +
> + return 1;
> +}
> +
> static struct user_namespace *pidns_owner(struct ns_common *ns)
> {
> return to_pid_ns(ns)->user_ns;
