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. > >> We could have a way to ask execve not to reinit the list. Such a >> mechanism would have to require no_new_privs to prevent a >> straightforward attack on any setuid binary. > > If we don't add a cred for every open fd, then I think we need this. If > we do, then I'm not sure this makes sense. See above. I think I'm misunderstanding you. > >> We's also want PR_SET_DUMPABLE or a new prctl to be able reset the >> list to contain just current-.cred, I think. > > Yeah PR_SET_DUMPABLE should reset it, agreed. > > -serge --Andy -- 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/