[ 3.5.y.z extended stable ] Patch "sysfs: fix race between readdir and lseek" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    sysfs: fix race between readdir and lseek

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 0fb9e36239be94ac8450574a1e8569a6dfb8b96e Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei at canonical.com>
Date: Wed, 20 Mar 2013 23:25:24 +0800
Subject: [PATCH] sysfs: fix race between readdir and lseek

commit 991f76f837bf22c5bb07261cfd86525a0a96650c upstream.

While readdir() is running, lseek() may set filp->f_pos as zero,
then may leave filp->private_data pointing to one sysfs_dirent
object without holding its reference counter, so the sysfs_dirent
object may be used after free in next readdir().

This patch holds inode->i_mutex to avoid the problem since
the lock is always held in readdir path.

Reported-by: Dave Jones <davej at redhat.com>
Tested-by: Sasha Levin <levinsasha928 at gmail.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Ming Lei <ming.lei at canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
[ luis: backported to 3.5: removed usage of file_inode() ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/sysfs/dir.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 2ee0864..8777436 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -1063,10 +1063,21 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
 	return 0;
 }

+static loff_t sysfs_dir_llseek(struct file *file, loff_t offset, int whence)
+{
+	struct inode *inode = file->f_path.dentry->d_inode;
+	loff_t ret;
+
+	mutex_lock(&inode->i_mutex);
+	ret = generic_file_llseek(file, offset, whence);
+	mutex_unlock(&inode->i_mutex);
+
+	return ret;
+}

 const struct file_operations sysfs_dir_operations = {
 	.read		= generic_read_dir,
 	.readdir	= sysfs_readdir,
 	.release	= sysfs_dir_release,
-	.llseek		= generic_file_llseek,
+	.llseek		= sysfs_dir_llseek,
 };
--
1.8.1.2