linux-kernel - [PATCH driver-core-next] sysfs: fix use-after-free in sysfs_kill

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Date:	Tue, 10 Dec 2013 10:22:30 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Yuanhan Liu <yuanhan.liu@...ux.intel.com>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org
Subject: [PATCH driver-core-next] sysfs: fix use-after-free in sysfs_kill_sb()

>From e09aae4796ac5b90c6514fc9789fc259bf783129 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@...nel.org>
Date: Tue, 10 Dec 2013 10:16:30 -0500

While restructuring the [u]mount path, 4b93dc9b1c68 ("sysfs, kernfs:
prepare mount path for kernfs") incorrectly updated sysfs_kill_sb() so
that it first kills super_block and then tries to dereference its
namespace tag to drop it.  Fix it by caching namespace tag before
killing the superblock and then drop the cached namespace tag.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Yuanhan Liu <yuanhan.liu@...ux.intel.com>
Tested-by: Yuanhan Liu <yuanhan.liu@...ux.intel.com>
Tested-by: Vlastimil Babka <vbabka@...e.cz>
Link: http://lkml.kernel.org/g/20131205031051.GC5135@yliu-dev.sh.intel.com
---
 fs/sysfs/mount.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index e7e3aa8..8d07527 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -45,8 +45,10 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
 
 static void sysfs_kill_sb(struct super_block *sb)
 {
+	void *ns = (void *)kernfs_super_ns(sb);
+
 	kernfs_kill_sb(sb);
-	kobj_ns_drop(KOBJ_NS_TYPE_NET, (void *)kernfs_super_ns(sb));
+	kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
 }
 
 static struct file_system_type sysfs_fs_type = {
-- 
1.8.4.2

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