linux-kernel - [PATCH] CGroups: Fix a race between rmdir and remount

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <6599ad830812101533r6cb007eeu5ef19499e278f6b7@mail.gmail.com>
Date:	Wed, 10 Dec 2008 15:33:12 -0800
From:	Paul Menage <menage@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] CGroups: Fix a race between rmdir and remount

Fix a race between rmdir and remount

When a cgroup is removed, it's unlinked from its parent's children
list, but not actually freed until the last dentry on it is released
(at which point cgrp->root->number_of_cgroups is decremented).

Currently rebind_subsystems checks for the top cgroup's child list
being empty in order to rebind subsystems into or out of a hierarchy -
this can result in the set of subsystems bound to a hierarchy being
different than the set of subsystems with state in the
removed-but-not-freed cgroup.

The simplest fix for this is to forbid remounts that change the set of
subsystems on a hierarchy that has removed-but-not-freed cgroups.

This bug can be reproduced via:

mkdir /mnt/cg
mount -t cgroup -o ns,freezer cgroup /mnt/cg
mkdir /mnt/cg/foo
sleep 1h < /mnt/cg/foo &
rmdir /mnt/cg/foo
mount -t cgroup -o remount,ns,devices,freezer cgroup /mnt/cg
kill $!

Signed-off-by: Paul Menage <menage@...gle.com>

---
 kernel/cgroup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: hierarchy_lock-mmotm-2008-12-09/kernel/cgroup.c
===================================================================
--- hierarchy_lock-mmotm-2008-12-09.orig/kernel/cgroup.c
+++ hierarchy_lock-mmotm-2008-12-09/kernel/cgroup.c
@@ -702,7 +702,7 @@ static int rebind_subsystems(struct cgro
 	 * any child cgroups exist. This is theoretically supportable
 	 * but involves complex error handling, so it's being left until
 	 * later */
-	if (!list_empty(&cgrp->children))
+	if (root->number_of_cgroups > 1)
 		return -EBUSY;

 	/* Process each subsystem */
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/