Messages in this thread | | | Date | Sat, 26 Dec 2015 02:10:38 +0100 | From | Jann Horn <> | Subject | Re: [PATCH] ptrace: being capable wrt a process requires mapped uids/gids |
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On Sat, Dec 12, 2015 at 09:12:41PM +0100, Jann Horn wrote: > With this change, the entering process can first enter the > namespace and then safely inspect the namespace's > properties, e.g. through /proc/self/{uid_map,gid_map}, > assuming that the namespace owner doesn't have access to > uid 0.
Actually, I think I missed something there. Well, at least it should not directly lead to a container escape.
> -static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode) > +static bool ptrace_has_cap(const struct cred *tcred, unsigned int mode) > { > + struct user_namespace *tns = tcred->user_ns; > + struct user_namespace *curns = current_cred()->user_ns; > + > + /* When a root-owned process enters a user namespace created by a > + * malicious user, the user shouldn't be able to execute code under > + * uid 0 by attaching to the root-owned process via ptrace. > + * Therefore, similar to the capable_wrt_inode_uidgid() check, > + * verify that all the uids and gids of the target process are > + * mapped into the current namespace. > + * No fsuid/fsgid check because __ptrace_may_access doesn't do it > + * either. > + */ > + if (!kuid_has_mapping(curns, tcred->euid) || > + !kuid_has_mapping(curns, tcred->suid) || > + !kuid_has_mapping(curns, tcred->uid) || > + !kgid_has_mapping(curns, tcred->egid) || > + !kgid_has_mapping(curns, tcred->sgid) || > + !kgid_has_mapping(curns, tcred->gid)) > + return false; > + > if (mode & PTRACE_MODE_NOAUDIT) > - return has_ns_capability_noaudit(current, ns, CAP_SYS_PTRACE); > + return has_ns_capability_noaudit(current, tns, CAP_SYS_PTRACE); > else > - return has_ns_capability(current, ns, CAP_SYS_PTRACE); > + return has_ns_capability(current, tns, CAP_SYS_PTRACE); > }
If the namespace owner can run code in the init namespace, the kuids are mapped into curns but he is still capable wrt the target namespace.
I think a proper fix should first determine the highest parent of tcred->user_ns in which the caller still has privs, then do the kxid_has_mapping() checks in there. [unhandled content-type:application/pgp-signature] | |