[PATCH 056/102] sysfs: fix race between readdir and lseek

From: Luis Henriques
Date: Mon Apr 08 2013 - 06:09:31 EST -stable review patch. If anyone has any objections, please let me know.


From: Ming Lei <ming.lei@xxxxxxxxxxxxx>

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@xxxxxxxxxx>
Tested-by: Sasha Levin <levinsasha928@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[ luis: backported to 3.5: removed usage of file_inode() ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
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,

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