linux-kernel - [21/74] sysfs: fix race between readdir and lseek

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Date:	Sun, 07 Apr 2013 23:45:42 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"Sasha Levin" <levinsasha928@...il.com>,
	"Dave Jones" <davej@...hat.com>,
	"Ming Lei" <ming.lei@...onical.com>
Subject: [21/74] sysfs: fix race between readdir and lseek

3.2.43-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Ming Lei <ming.lei@...onical.com>

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@...hat.com>
Tested-by: Sasha Levin <levinsasha928@...il.com>
Signed-off-by: Ming Lei <ming.lei@...onical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.2: open-code file_inode() which we don't have]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/sysfs/dir.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -1023,10 +1023,21 @@ static int sysfs_readdir(struct file * f
 	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,
 };

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