linux-kernel - [CFT][PATCH 7/7] userns: Allow setting gid_maps without privilege when setgroups is disabled

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Message-ID: <87egs9pz5u.fsf_-_@x220.int.ebiederm.org>
Date:	Mon, 08 Dec 2014 16:14:21 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linux Containers <containers@...ts.linux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	Linux API <linux-api@...r.kernel.org>,
	linux-man <linux-man@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Richard Weinberger <richard@....at>,
	Kenton Varda <kenton@...dstorm.io>,
	stable <stable@...r.kernel.org>
Subject: [CFT][PATCH 7/7] userns: Allow setting gid_maps without privilege when setgroups is disabled


Now that setgroups can be disabled and not reenabled, setting gid_map
without privielge can now be enabled when setgroups is disabled.

This restores most of the functionality that was lost when unprivilege
setting of gid_map was removed.  Applications that use this
functionality will need to check to see if they use setgroups or
init_groups, and if they don't they can be fixed by simply
disabling of setgroups before they run.

Cc: stable@...r.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/user_namespace.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 3d128f91ced3..459c7f647072 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -828,6 +828,11 @@ static bool new_idmap_permitted(const struct file *file,
 			kuid_t uid = make_kuid(ns->parent, id);
 			if (uid_eq(uid, cred->euid))
 				return true;
+		} else if (cap_setid == CAP_SETGID) {
+			kgid_t gid = make_kgid(ns->parent, id);
+			if (!userns_setgroups_allowed(ns) &&
+			    gid_eq(gid, cred->egid))
+				return true;
 		}
 	}
 
-- 
1.9.1

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