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SubjectRe: [RFC][PATCH 6/6][v3] Protect cinit from blocked fatal signals
On 12/20, Sukadev Bhattiprolu wrote:
>
> +static int sig_unkillable(struct signal_struct *signal, int sig)
> +{
> + if (signal->flags & SIGNAL_UNKILLABLE_FROM_NS)
> + return !sig_kernel_only(sig);
> +
> + /*
> + * We must have dropped SIGKILL/SIGSTOP in sig_ignored()
> + * TODO: Remove BUG_ON().
> + */
> + BUG_ON(signal->flags & SIGNAL_UNKILLABLE && sig_kernel_only(sig));
> +
> + return (signal->flags & SIGNAL_UNKILLABLE);
> +}
> +
> int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
> struct pt_regs *regs, void *cookie)
> {
> @@ -1907,9 +1943,10 @@ relock:
>
> /*
> * Global init gets no signals it doesn't want.
> + * Container-init gets no signals it doesn't want from same
> + * container.
> */
> - if (unlikely(signal->flags & SIGNAL_UNKILLABLE) &&
> - !signal_group_exit(signal))
> + if (sig_unkillable(signal, signr) && !signal_group_exit(signal))
> continue;

Again, I do not understand why do we need SIGNAL_UNKILLABLE_FROM_NS.

I thought about the change in get_signal_to_deliver() during the
previous discussion, and I think what we need is:

if (unlikely(signal->flags & SIGNAL_UNKILLABLE) &&
!sig_kernel_only(sig))
continue;

and this was yet another reason for "protect init from unwanted signals more".

Because, if we see SIGKILL/SIGSTOP here, this means that the signal
was sent from the parent ns, or it was generated "internally", for
example by sys_exit_group().

Oleg.



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