Re: [PATCH 2/5] kernel: add a helper to get an owning user namespace for a namespace
From: Eric W. Biederman <hidden>
Date: 2016-07-24 05:16:57
Also in:
linux-fsdevel, lkml
Andrey Vagin [off-list ref] writes:
quoted hunk
Return -EPERM if an owning user namespace is outside of a process current user namespace.diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index a5bc78c..6382e5e 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c@@ -994,6 +994,30 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns) return commit_creds(cred); } +struct ns_common *ns_get_owner(struct ns_common *ns) +{ + const struct cred *cred = current_cred(); + struct user_namespace *user_ns, *p; + + user_ns = p = ns->user_ns; + if (user_ns == NULL) { /* ns is init_user_ns */ + /* Unprivileged user should not know that it's init_user_ns. */ + if (capable(CAP_SYS_ADMIN)) + return ERR_PTR(-ENOENT); + return ERR_PTR(-EPERM); + }
This permission check is not what I meant to request. This does not handle nested user namespaces.
+ for (;;) {
+ if (p == cred->user_ns)
+ break;
+ if (p == &init_user_ns)
+ return ERR_PTR(-EPERM);
+ p = p->parent;
+ }
+
The permission check really needs to be down here. And be:
if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return ERR_PTR(-EPERM).
That cleanly and easily handles more than a depth of a single user
namespace.
+ return &get_user_ns(user_ns)->ns;
+}
+
const struct proc_ns_operations userns_operations = {
.name = "user",
.type = CLONE_NEWUSER,Eric