On 9/5/20, Philip Guenther <guent...@gmail.com> wrote:
> On Fri, Sep 4, 2020 at 2:59 PM Mateusz Guzik <mjgu...@gmail.com> wrote:
>
>> On 9/5/20, Philip Guenther <guent...@gmail.com> wrote:
>> > On Fri, Sep 4, 2020 at 1:06 PM Mateusz Guzik <mjgu...@gmail.com> wrote:
>> >
>> >> On 9/4/20, Vitaliy Makkoveev <m...@openbsd.org> wrote:
>> >> > On Fri, Sep 04, 2020 at 05:24:42PM +0200, Mateusz Guzik wrote:
>> >> >> getppid blindly follows the parent pointer and reads the pid.
>> >> >>
>> >> >> The problem is that ptrace reparents the traced process, so in
>> >> >> particular if you gdb -p $something, the target proc will start
>> seeing
>> >> >> gdb instead of its actual parent.
>> >> >>
>> >> >> There is a lot to say about the entire reparenting business or
>> storing
>> >> >> the original pid in ps_oppid (instead of some form of a reference
>> >> >> to
>> >> >> the process).
>> >> >>
>> >> >> However, I think the most feasible fix for now is the same thing
>> >> >> FreeBSD did: *always* store the actual parent pid in ps_oppid. This
>> >> >> means all repareting will keep updating it (most notably when
>> >> >> abandoning children on exit), while ptrace will skip that part.
>> >> >>
>> >> >> Side effect of such a change be that getppid will stop requiring
>> >> >> the
>> >> >> kernel lock.
>> >> >>
>> >> >
>> >> > Thanks for report. But we are in beta stage now so such modification
>> is
>> >> > impossible until next iteration.
>> >> >
>> >> > Since original parent identifier is stored as `ps_oppid' while
>> >> > process
>> >> > is traced we just return it to userland for this case. This is the
>> >> > way
>> >> > I
>> >> > propose to fix this bug for now.
>> >> >
>> >> > Comments? OKs?
>> >> >
>> >> > Index: sys/kern/kern_prot.c
>> >> > ===================================================================
>> >> > RCS file: /cvs/src/sys/kern/kern_prot.c,v
>> >> > retrieving revision 1.76
>> >> > diff -u -p -r1.76 kern_prot.c
>> >> > --- sys/kern/kern_prot.c 9 Jul 2019 12:23:25 -0000 1.76
>> >> > +++ sys/kern/kern_prot.c 4 Sep 2020 21:12:15 -0000
>> >> > @@ -84,7 +84,11 @@ int
>> >> > sys_getppid(struct proc *p, void *v, register_t *retval)
>> >> > {
>> >> >
>> >> > - *retval = p->p_p->ps_pptr->ps_pid;
>> >> > + if (p->p_p->ps_flags & PS_TRACED)
>> >> > + *retval = p->p_p->ps_oppid;
>> >> > + else
>> >> > + *retval = p->p_p->ps_pptr->ps_pid;
>> >> > +
>> >> > return (0);
>> >> > }
>> >>
>> >> This is definitely a bare minimum fix, but it does the job.
>> >>
>> >
>> > ptrace() has behaved like this for the life of OpenBSD and an
>> > indefinite
>> > number of years previous in the BSD releases. What has happened that a
>> > definitely incomplete fix is needed Right Now?
>>
>> I don't see how this reads as a demand this is fixed Right Now.
>>
>
> I didn't call it a demand, but the point stands: what has changed?
>
Nothing has changed. I don't use the system apart from sometimes
testing stuff in a VM. There is 0 pressure on my end to fix this.
>
> I don't see how the fix is incomplete either. It can be done better
>> with more effort, but AFAICS the above results in correct behavior.
>>
>
> There are at least 2 other uses of ps_pptr->ps_pid that should also change,
> unless you like coredumps and ps disagreeing with getppid(), and someone
> needs to think how it affects doas.
>
I see, I did not grep for these.
--
Mateusz Guzik <mjguzik gmail.com>
