From: Eric W. Biederman <ebiederm@xmission.com>
Date: Sat, 6 Dec 2014 00:01:11 +0000 (-0600)
Subject: userns: Don't allow setgroups until a gid mapping has been setablished
X-Git-Tag: omap-for-v3.20/drop-legacy-3517~45^2~8
X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=273d2c67c3e179adb1e74f403d1e9a06e3f841b5;p=pandora-kernel.git

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 <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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