Messages in this thread | | | From | (Eric W. Biederman) | Date | Thu, 14 Mar 2013 13:29:10 -0700 | Subject | Re: CLONE_NEWUSER|CLONE_FS root exploit |
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Andy Lutomirski <luto@amacapital.net> writes:
> On 03/13/2013 11:35 AM, Eric W. Biederman wrote: >> Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> 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 <ebiederm@xmission.com> 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
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