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SubjectRe: [PATCH] kernel/signal: Signal-based pre-coredump notification
On 10/12, Enke Chen wrote:
>
> For simplicity and consistency, this patch provides an implementation
> for signal-based fault notification prior to the coredump of a child
> process. A new prctl command, PR_SET_PREDUMP_SIG, is defined that can
> be used by an application to express its interest and to specify the
> signal (SIGCHLD or SIGUSR1 or SIGUSR2) for such a notification. A new
> signal code (si_code), CLD_PREDUMP, is also defined for SIGCHLD.

To be honest, I can't say I like this new feature...

> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -696,6 +696,10 @@ struct task_struct {
> int exit_signal;
> /* The signal sent when the parent dies: */
> int pdeath_signal;
> +
> + /* The signal sent prior to a child's coredump: */
> + int predump_signal;
> +

At least, I think predump_signal should live in signal_struct, not
task_struct.

(pdeath_signal too, but it is too late to change (fix) this awkward API).

> +static void do_notify_parent_predump(struct task_struct *tsk)
> +{
> + struct sighand_struct *sighand;
> + struct task_struct *parent;
> + struct kernel_siginfo info;
> + unsigned long flags;
> + int sig;
> +
> + parent = tsk->real_parent;

So, debuggere won't be notified, only real_parent...

> + sig = parent->predump_signal;

probably ->predump_signal should be cleared on exec?

> + /* Check again with tasklist_lock" locked by the caller */
> + if (!valid_predump_signal(sig))
> + return;

I don't understand why we need valid_predump_signal() at all.

> bool get_signal(struct ksignal *ksig)
> {
> struct sighand_struct *sighand = current->sighand;
> @@ -2497,6 +2535,19 @@ bool get_signal(struct ksignal *ksig)
> current->flags |= PF_SIGNALED;
>
> if (sig_kernel_coredump(signr)) {
> + /*
> + * Notify the parent prior to the coredump if the
> + * parent is interested in such a notificaiton.
> + */
> + int p_sig = current->real_parent->predump_signal;
> +
> + if (valid_predump_signal(p_sig)) {
> + read_lock(&tasklist_lock);
> + do_notify_parent_predump(current);
> + read_unlock(&tasklist_lock);
> + cond_resched();

perhaps this should be called by do_coredump() after coredump_wait() kills
all the sub-threads?

> +static int prctl_set_predump_signal(struct task_struct *tsk, pid_t pid, int sig)
> +{
> + struct task_struct *p;
> + int error;
> +
> + /* 0 is valid for disabling the feature */
> + if (sig && !valid_predump_signal(sig))
> + return -EINVAL;
> +
> + /* For the current task, the common case */
> + if (pid == 0) {
> + tsk->predump_signal = sig;
> + return 0;
> + }
> +
> + error = -ESRCH;
> + rcu_read_lock();
> + p = find_task_by_vpid(pid);
> + if (p) {
> + if (!set_predump_signal_perm(p))
> + error = -EPERM;
> + else {
> + error = 0;
> + p->predump_signal = sig;
> + }
> + }
> + rcu_read_unlock();
> + return error;
> +}

Why? I mean, why do we really want to support the pid != 0 case?

Oleg.

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