userns: Don't allow setgroups until a gid mapping has been setablished
authorEric W. Biederman <ebiederm@xmission.com>
Sat, 6 Dec 2014 00:01:11 +0000 (18:01 -0600)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 8 Jan 2015 17:58:16 +0000 (09:58 -0800)
commitfc9b65e3d7703e6d63875b0b233bbe26a4a513ba
tree7686f17848a927d80398803eab339cb9084343ed
parentb8a0441b542f6d6bd6fda46cc735ae71392cb845
userns: Don't allow setgroups until a gid mapping has been setablished

commit 273d2c67c3e179adb1e74f403d1e9a06e3f841b5 upstream.

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.

Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
include/linux/user_namespace.h
kernel/groups.c
kernel/user_namespace.c