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Re: [libvirt] [PATCH 3/4] lxc: validate container process during load config



On Fri, May 30, 2008 at 11:40:00AM -0700, Dave Leskovec wrote:
> Daniel P. Berrange wrote:
> > On Fri, May 30, 2008 at 02:28:46AM -0400, Daniel Veillard wrote:
> >> On Thu, May 29, 2008 at 03:20:15PM -0700, Dave Leskovec wrote:
> >>> +            if (ESRCH == errno) {
> >>> +                rc = 0;
> >>> +                DEBUG("pid %d no longer exists", def->id);
> >>> +                goto done;
> >>> +            }
> >>> +
> >>> +            lxcError(NULL, NULL, VIR_ERR_INTERNAL_ERROR,
> >>> +                     _("error checking container process: %d %s"),
> >>> +                     def->id, strerror(errno));
> >>> +            goto done;
> >>> +        }
> >>   The problem though is that by doing just  a passive test for the PID
> >> it feels like there is a possible race if the process counter rolled over and
> >> another process with the same PID got create in the meantime.
> >>   i have the feeling that a test based on the state of the file descriptors
> >> used to communicate with the container would be more reliable. Basically if the
> >> container disapear, then the pipe should get in a half-closed state, 
> >> detecting the change at that level sounds like it would be more reliable,
> >> don't you think so ?
> > 
> > Yes, after checking the PID still exists, it needs to validate /proc/$PID/exe
> > to verify it points to the binary we expect it to.
> 
> Hmmm....  Worked with this a bit and I don't think we can reliably know what to
> expect /proc/$PID/exe to point to.  For scripts, /proc/$PID/exe seems to point
> the shell.  Also, if the container does an exec, /proc/$PID/exe points to
> whatever it exec'd rather than the init program.

Well the path won't change once launched, so why not store the original
value of /proc/$PID/exe in the /var/lib/libivrt/lxc/NAME.pid  file too,
so you can read it back out later & validate.

Dan.
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