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.
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