Andy Lutomirski <[email protected]> writes: > On 03/13/2013 11:35 AM, Eric W. Biederman wrote: >> Kees Cook <[email protected]> writes: >> >>> Hi, >>> >>> It seem like we should block (at least) this combination. On 3.9, this >>> exploit works once uidmapping is added. >>> >>> http://www.openwall.com/lists/oss-security/2013/03/13/10 >> >> Yes. That is a bad combination. It let's chroot confuse privileged >> processes. >> >> Now to figure out if this is easier to squash by adding a user_namespace >> to fs_struct or by just forbidding this combination. > > It's worth making sure that setns(2) doesn't have similar issues.
setns(2) and unshare(2) are done and merged. See commit. commit e66eded8309ebf679d3d3c1f5820d1f2ca332c71 Author: Eric W. Biederman <[email protected]> Date: Wed Mar 13 11:51:49 2013 -0700 userns: Don't allow CLONE_NEWUSER | CLONE_FS > Looking through other shared-but-not-a-namespace things, there are: > > fs_struct: Buggy as noted. > > files_struct: Probably harmless -- SCM_RIGHTS can emulate it > > signal_struct: This interacts with the tty code. Is it okay? It should be. The tty code is heavily pid based, and CLONE_NEWPID requires !CLONE_VM (which implies !CLONE_SIGHAND and !CLONE_VM). > sighand_struct: Looks safe. Famous last words. > > FWIW, I've been alarmed in the past that struct path (e.g. the root > directory) implies an mnt_namespace (hidden in struct mount), and it's > entirely possible for the root directory's mnt_namespace not to match > nsproxy->mnt_namespace. I'm not sure what the implications are, but > this doesn't seem healthy. The calls to check_mnt prevent abuse of the files found with fs_struct not matching the current mount namespace. static inline int check_mnt(struct mount *mnt) { return mnt->mnt_ns == current->nsproxy->mnt_ns; } Thanks for looking I know I did the same double take and wondered if I had missed anything else by accident when this bug showed up. So far even just looking it all over again I can't see anything. But I have clearly been blind before. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
