linux-kernel - [PATCH 3.13.y-ckt 112/139] userns: Allow setting gid_maps without privilege when setgroups is disabled

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Message-Id: <1422483682-15393-113-git-send-email-kamal@canonical.com>
Date:	Wed, 28 Jan 2015 14:20:55 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.13.y-ckt 112/139] userns: Allow setting gid_maps without privilege when setgroups is disabled

3.13.11-ckt15 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@...ssion.com>

commit 66d2f338ee4c449396b6f99f5e75cd18eb6df272 upstream.

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 unprivileged
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 setgroups before writing to
gid_map.

Reviewed-by: Andy Lutomirski <luto@...capital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 kernel/user_namespace.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index d03d490..722bd12 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -818,6 +818,11 @@ 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 (!(ns->flags & USERNS_SETGROUPS_ALLOWED) &&
+			    gid_eq(gid, cred->egid))
+				return true;
 		}
 	}
 
-- 
1.9.1

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