Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 29 Jul 2014 21:05:42 -0700 | Subject | Re: [PATCH 11/11] seccomp: Add tgid and tid into seccomp_data |
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On Mon, Jul 28, 2014 at 2:18 PM, Eric W. Biederman <ebiederm@xmission.com> wrote: > Andy Lutomirski <luto@amacapital.net> writes: > >> [cc: Eric Biederman] >> > >> Can we do one better and add a flag to prevent any non-self pid >> lookups? This might actually be easy on top of the pid namespace work >> (e.g. we could change the way that find_task_by_vpid works). >> >> It's far from just being signals. There's access_process_vm, ptrace, >> all the signal functions, clock_gettime (see CPUCLOCK_PID -- yes, this >> is ridiculous), and probably some others that I've forgotten about or >> never noticed in the first place. > > So here is the practical question. > > Are these processes that only can send signals to their thread group > allowed to call fork()? > > > If fork is allowed and all pid lookups are restricted to their own > thread group that wait, waitpid, and all of the rest of the wait family > will never return the pids of their children, and zombies will > accumulate. Aka the semantics are fundamentally broken.
Good point.
I can imagine at least three ways that fork() could continue working, though:
1. Allow lookups of immediate children, too. (I don't love this one.) 2. Allow non-self pids to be translated in but not out. This way P_ALL will continue working. 3. Have the kernel treat any PID-restricted process as though it were NOCLDWAIT.
I think I like #3. Thoughts?
> > If fork is not allowed pid namespaces already solve this problem.
PID namespaces are fairly heavyweight. Julien pointed out that using PID namespaces requires a bunch of dummy PID 1 processes.
--Andy
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