On Sat, 2018-11-17 at 19:20 -0800, Zac Medico wrote:
> On 11/14/18 12:02 AM, Michał Górny wrote:
> > @@ -531,6 +543,15 @@ def _exec(binary, mycommand, opt_name, fd_pipes, env,
> > gid, groups, uid, umask,
> >
> > errno.errorcode.get(ctypes.get_errno(), '?')),
> > noiselevel=-1)
> > else:
> > + if unshare_pid:
> > + # pid namespace
> > requires us to become init
> > + # TODO: do init-ty stuff
> > + # therefore, fork() ASAP
> > + fork_ret = os.fork()
> > + if fork_ret != 0:
> > + pid, status =
> > os.waitpid(fork_ret, 0)
> > + assert pid ==
> > fork_ret
> > + os._exit(status)
> > if unshare_mount:
> > # mark the whole
> > filesystem as private to avoid
> > # mounts escaping the
> > namespace
> > @@ -541,6 +562,18 @@ def _exec(binary, mycommand, opt_name, fd_pipes, env,
> > gid, groups, uid, umask,
> > # TODO: should
> > it be fatal maybe?
> >
> > writemsg("Unable to mark mounts private: %d\n" % (mount_ret,),
> >
> > noiselevel=-1)
> > + if unshare_pid:
> > + if mount_ret != 0:
> > + # can't proceed
> > without private mounts
> > + os._exit(1)
>
> For the benefit of anyone not watching
> https://github.com/gentoo/portage/pull/379, the mount_ret is expected
> to be non-zero inside a chroot where `mount --make-rprivate /` would
> fail because / is not a mountpoint, and this is an extremely valuable
> use case for tools like catalyst that perform builds inside a chroot.
>
> Based on /proc/[pid]/mountinfo documentation in the proc(5) manpage,
> and empirical analysis of /proc/self/mountinfo in various states,
> it should be reasonable to assume that the current propagation flags
> are suitable if there is not a shared / or /proc mountpoint found in
> /proc/self/mountinfo. We can use a function like this to check if the
> `mount --make-rprivate /` call is needed:
>
> def want_make_rprivate():
> try:
> with open('/proc/self/mountinfo', 'rb') as f:
> if re.match(rb'^\S+ \S+ \S+ \S+ (?P<mountpoint>/|/proc) \S+
> (?:\S+:\S+ )*(?P<shared>shared:\S+ )', f.read(), re.MULTILINE) is None:
> return False
> except EnvironmentError:
> pass
> return TrueTechnically speaking, FEATURES=mount-sandbox goes beyond /proc, so making it guess based on the state of /proc is wrong. Yes, we need only /proc for the purpose of pid-sandbox but we shouldn't presume the user wouldn't want more. Maybe we should split the logic more, and e.g. be more fatal about --make-rprivate failing when mount-sandbox is explicitly used, and only care about /proc when pid-sandbox is only used. In the latter case, it probably doesn't make sense to check but just try to --make-private /proc. /proc is naturally a mountpoint, so it should cause no harm to privatize it. Also, after some extra reading I think we should use 'slave' instead of 'private'. Having things implicitly 'private' might be surprising since user's actions won't propagate into the build namespace, and I think we want them to propagate. -- Best regards, Michał Górny
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