On Tue, Oct 7, 2014 at 4:42 PM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: > Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes: > >> On Tue, Oct 7, 2014 at 3:42 PM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: >>> Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes: >>> >>>> On Tue, Oct 7, 2014 at 2:42 PM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: >>>>> >>>>> I am squinting and looking this way and that but while I can imagine >>>>> someone more clever than I can think up some unique property of rootfs >>>>> that makes it a little more exploitable than just mounting a ramfs, >>>>> but since you have to be root to exploit those properties I think the >>>>> game is pretty much lost. >>>> >>>> Yes. rootfs might not be empty, it might have totally insane >>>> permissions, and it's globally shared, which makes it into a wonderful >>>> channel to pass things around that shouldn't be passed around. >>> >>> But if only root with proc mounted can reach it... I don't know. >> >> It doesn't have to be global root. It could be userns root. >> >>> There might be a case for setting MNT_LOCKED when we overmount "/" >>> as root but I don't yet see it. >>> >>>> Can non-root do this? You'd need to be in a userns with a "/" that >>>> isn't MNT_LOCKED. Can this happen on any normal setup? >>>> >>>> FWIW, I think we should unconditionally MNT_LOCKED the root on userns >>>> unshare, even if it's the only mount. >>> >>> To the best of my knowledge MNT_LOCKED is set uncondintially on userns >>> unshare. >> >> Only if list_empty(&old->mnt_expire), whatever that means, I think. > > An autofs or nfs automounted mount. Can those ever become root? Dunno. I thought that this code was what set MNT_LOCKED for things that should be locked: /* Don't allow unprivileged users to reveal what is under a mount */ if ((flag & CL_UNPRIVILEGED) && list_empty(&old->mnt_expire)) mnt->mnt.mnt_flags |= MNT_LOCKED; Now I'm confused. Shouldn't that be checking for submounts? Is that what it's doing? Anyway, I think that this should unconditionally set MNT_LOCKED on the thing that mounted on rootfs. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html