Re: [RFC][PATCH 3/7][v4] Define siginfo_from_ancestor_ns()

Oleg Nesterov
2008-12-24T16:30:26Z

On 12/24, Sukadev Bhattiprolu wrote:
>
> +#ifdef CONFIG_PID_NS
> +static inline int siginfo_from_user(siginfo_t *info)
> +{
> + if (!is_si_special(info) && SI_FROMUSER(info) &&
> + info->si_code != SI_ASYNCIO)
> + return 1;
> +
> + return 0;
> +}
> +#else
> +static inline int siginfo_from_user(siginfo_t *info)
> +{
> + return 0;
> +}
> +#endif
> +
> +static inline int siginfo_from_ancestor_ns(struct task_struct *t,
> + siginfo_t *info)
> +{
> + struct pid_namespace *ns;
> +
> + /*
> + * Ensure signal is from user-space before checking pid namespace
> + */
> + if (siginfo_from_user(info)) {
> + /*
> + * If we do not have a pid in the receiver's namespace,
> + * we must be an ancestor of the receiver.
> + *
> + * CHECK:
> + * If receiver is exiting, ns == NULL, signal will be
> + * queued but ignored (wants_signal() is FALSES). For
> + * compatibility with current behavior, assume it is
> + * from ancestor and queue the signal anyway ?
> + */
> + ns = task_active_pid_ns(t);
> + if (!ns || task_pid_nr_ns(current, ns) <= 0)
> + return 1;
> + }
> +
> + return 0;
> +}

Small nit... siginfo_from_user() is only called by siginfo_from_ancestor_ns().
The first helper depends on CONFIG_PID_NS, the second is not. A bit strange.

Isn't it cleaner to do

#ifdef CONFIG_PID_NS
static inline int siginfo_from_user(siginfo_t *info)
{
...
}
static inline int siginfo_from_ancestor_ns(...)
{
...
}
#else
static inline int siginfo_from_ancestor_ns(...)
{
return 0;
}
#endif

?

> +#ifdef CONFIG_PID_NS
> +/*
> + * siginfo_from_user() assumes that si_code SI_ASYNCIO comes only from
> + * within the kernel. If an application is passing in SI_ASYNCIO we
> + * want to know about it.
> + */
> +static void warn_on_asyncio(siginfo_t *info)
> +{
> + WARN_ON_ONCE(info->si_code == SI_ASYNCIO);
> +}
> +#else
> +#define warn_on_asyncio(info) {}
> +#endif
> +
> asmlinkage long
> sys_rt_sigqueueinfo(pid_t pid, int sig, siginfo_t __user *uinfo)
> {
> @@ -2324,6 +2388,9 @@ sys_rt_sigqueueinfo(pid_t pid, int sig, siginfo_t __user *uinfo)
> Nor can they impersonate a kill(), which adds source info. */
> if (info.si_code >= 0)
> return -EPERM;
> +
> + warn_on_asyncio(&info);

Hmm... why do you want this? The user-space can use any si_code >= 0,
why should we uglify the code?

And, SI_ASYNCIO only matters when we send the signal to the subnamespace,
and in that case we will probably mangle .si_pid. So why don't we warn
when .si_code == SI_USER?

Oleg.