From 273d2c67c3e179adb1e74f403d1e9a06e3f841b5 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 5 Dec 2014 18:01:11 -0600 Subject: userns: Don't allow setgroups until a gid mapping has been setablished setgroups is unique in not needing a valid mapping before it can be called, in the case of setgroups(0, NULL) which drops all supplemental groups. The design of the user namespace assumes that CAP_SETGID can not actually be used until a gid mapping is established. Therefore add a helper function to see if the user namespace gid mapping has been established and call that function in the setgroups permission check. This is part of the fix for CVE-2014-8989, being able to drop groups without privilege using user namespaces. Cc: stable@vger.kernel.org Reviewed-by: Andy Lutomirski Signed-off-by: "Eric W. Biederman" --- kernel/user_namespace.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'kernel/user_namespace.c') diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index b99c862a2e3f..27c8dab48c07 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -843,6 +843,20 @@ static bool new_idmap_permitted(const struct file *file, return false; } +bool userns_may_setgroups(const struct user_namespace *ns) +{ + bool allowed; + + mutex_lock(&id_map_mutex); + /* It is not safe to use setgroups until a gid mapping in + * the user namespace has been established. + */ + allowed = ns->gid_map.nr_extents != 0; + mutex_unlock(&id_map_mutex); + + return allowed; +} + static void *userns_get(struct task_struct *task) { struct user_namespace *user_ns; -- cgit v1.2.3