sysfs: fix race between readdir and lseek

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@redhat.com>
Tested-by: Sasha Levin <levinsasha928@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 2fbdff6be25c..c9e16608f486 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -1058,10 +1058,21 @@ 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_inode(file);
+        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,
 };