Quoting Andy Lutomirski (l...@amacapital.net): > On Fri, Apr 11, 2014 at 2:52 PM, Serge E. Hallyn <se...@hallyn.com> wrote: > > Quoting Andy Lutomirski (l...@amacapital.net): > >> On Mon, Apr 7, 2014 at 11:13 AM, Serge E. Hallyn <se...@hallyn.com> wrote: > >> > Quoting Andy Lutomirski (l...@amacapital.net): > >> >> I'm starting to think that we need to extend dumpable to something > >> >> much more general like a list of struct creds that someone needs to be > >> >> able to ptrace, *in addition to current creds* in order to access > >> >> sensitive /proc files, coredumps, etc. If you get started as setuid, > >> > > >> > Hm, yeah, this sort of makes sense. > >> > > >> >> then you start with two struct creds in the list (or maybe just your > >> >> euid and uid). If you get started !setuid, then your initial creds > >> >> are in the list. It's possible that few or no things will need to > >> >> change that list after execve. > >> >> > >> >> If all of the entries and current->cred are in the same user_ns, then > >> >> we can dump as userns root. If they're in different usernses, then we > >> >> dump as global root or maybe the common ancestor root. > >> >> setuid(getuid()) and other such nastiness may have to empty the list, > >> >> or maybe we can just use a prctl for that. > >> > > >> > A few questions, > >> > > >> > 1. is there any other action which would trigger adding a new cred to > >> > the ist? > >> > >> I don't think so. Anyone who can ptrace you from the start can > >> corrupt you such that you leak rights even if some future action > >> prevents new ptracers from attaching. > >> > >> OTOH, it might be nice for something like an HTTPS server to be able > >> to fork and shove its private key into the child, while preventing > >> anyone from ptracing the child. But doing this securely without help > >> from someone with a different uid might be impossible anyway. > >> > >> > > >> > 2. would execve clear (and re-init) the list of creds? > >> > >> Probably. Thoughts? > > > > Yeah it seems to me it should be re-initialized, with a cred added > > to the list for every open fd. > > What do you mean "every fd"? > > It seems odd to me that execve of anything that isn't setuid would add > anything to the list -- attackers can always ptrace before the execve > happens.
Maybe you're right. Maybe I shouldn't reason about this on a friday afternoon. My *thought* was setuid-root program opens /etc/shadow, then execs a regular program keeping that open. Attaching to that fails now though, presumably due to dumpable. -serge -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
