On 03/26, Grzegorz Nosek wrote:
>
> On Fri, Mar 26, 2010 at 12:11:31PM +0100, Oleg Nesterov wrote:
> > Yes, this is broken. More precisely, this wasn't even supposed to work.
> >
> > Even stracing of the sub-init itself (or global init btw) has problems,
> > the straced init is not protected from unwanted signals.
>
> Is this impossible/very hard to do cleanly? I understand that container's
> init becomes vulnerable to signals sent from root-owned processes in the
> container. If so, the impact of this issue should be quite limited, no?
Yes, probably we can ignore this.
> > Yes. First of all, tracehook_report_clone_complete() reports the wrong pid nr,
> > as it seen inside the init's namespace. This is easy to fix, but I doubt this
> > can help. IIRC strace doesn't use PTRACE_GETEVENTMSG at all, it looks at eax
> > after syscall.
> >
> > which patch?
>
> The patch below posted by Matt. AIUI, it fixes the
> tracehook_report_clone_complete() part, which results in an observable
> change in strace's behaviour (not that it makes strace work, though).
I guess it doesn't work because we need to fix strace, see "strace doesn't
use PTRACE_GETEVENTMSG" above.
> Anyway, are there any remaining issues on the kernel side or does strace
> have to be taught about pid namespaces?
At first glance, I don't see other problems, except sometimes the reported
pid is wrong (like in do_fork).
> + ptrace_pid_vnr = nr;
> + if (unlikely(p->parent != p->real_parent)) {
> + rcu_read_lock();
> + ptrace_pid_vnr = task_pid_nr_ns(p, p->parent->nsproxy->pid_ns);
Yes, this is what I meant.
But we should not do this in do_fork().
But once again. This change fixes the value in "tracee->ptrace_message == newpid",
but a quick grep shows that strace-4.5.19 doesn't use PTRACE_GETEVENTMSG at all.
Oleg.
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