"Thompson, David" <dthomps...@worcester.edu> skribis: > On Sat, Jun 13, 2015 at 4:19 PM, Ludovic Courtès <l...@gnu.org> wrote: >> "Thompson, David" <dthomps...@worcester.edu> skribis: >> >>> On Sat, Jun 13, 2015 at 9:06 AM, Ludovic Courtès <l...@gnu.org> wrote: >>>> "Thompson, David" <dthomps...@worcester.edu> skribis: >>>> >>>>> On Fri, Jun 12, 2015 at 11:12 AM, Ludovic Courtès <l...@gnu.org> wrote: >>>>>> "Thompson, David" <dthomps...@worcester.edu> skribis: >>>>>> >>>>>>> Yeah, our daemon would do the same thing. We could maybe even have a >>>>>>> little Guile library that allows one to evaluate arbitrary scheme code >>>>>>> from within the container. :) >>>>>> >>>>>> Actually, something quite easily feasible would be this: >>>>>> >>>>>> (eval-in-container #~(system* #$evil-program >>>>>> #$(local-file "important-data.txt")) >>>>>> #:networking? #f) >>>>>> >>>>>> ... where the container’s store would be populated with just >>>>>> EVIL-PROGRAM and the local file. >>>>>> >>>>>> Food for thought... >>>>> >>>>> Ooooh yeah! That would be cool. Though I think we should still spawn >>>>> a dmd process as PID 1 to deal with reaping zombie processes. We >>>>> could generate a single service that runs the gexp script. How does >>>>> that sound? >>>> >>>> Wouldn’t it be enough to have the Guile process that evaluates the >>>> expression be PID 1 in the container, as is the case in guix-daemon >>>> containers? >>> >>> Sure, it would work, but my concern is that a long-running process on >>> a user's machine could create and orphan tons of child processes and >>> nothing would be able to clean them up until the PID namespace is >>> garbage collected. >> >> My understanding was that killing a container’s PID 1 (from the outside) >> effectively killed all the processes of that PID name space. Isn’t it >> the case? > > Yes, that is the case. That triggers the "garbage collection" of that > namespace, if you will. My point is that, without a proper PID 1 that > can DTRT with orphaned processes, a long running process in a > container could potentially create a ton of orphaned child processes > with no way for them to be reaped without killing PID 1. I wouldn't > be very happy if a program that I was running in a sandbox was > polluting the process list. I don't think this is a concern for the > build daemon because the build process is a (relatively) short-lived > process, but running something like a web browser could go on for > days, weeks, etc.
Yes, I understand. This is definitely an important concern for full GuixSD containers. However, ‘eval-in-container’ would be much simpler, synchronous, and typically for short-lived processes. So I guess the process that runs ‘eval-in-container’ would clone(2) (via ‘call-with-container’) and simply waitpid(2) the child process (which is PID 1 in its container). When the parent process gets a SIGINT or SIGHUP, it could send SIGKILL to the child, thereby terminating the container. Does that make sense? >> (The daemon works around that by running processes under a separate UID >> and doing kill(-1, SIGKILL) under that UID.) > > So, PID 1 in the build container forks and changes the UID or > something? Yes, with setuid (see build.cc:2180.) Thanks, Ludo’.
