[PATCH 4.5 108/124] ext4: use file_dentry()

[Greg Kroah-Hartman]

4.5-stable review patch.  If anyone has any objections, please let me know.

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

From: Miklos Szeredi <mszeredi@xxxxxxxxxx>

commit c0a37d48788475d0a2cf4fbfaa28559a9de612fc upstream.

EXT4 may be used as lower layer of overlayfs and accessing f_path.dentry
can lead to a crash.

Fix by replacing direct access of file->f_path.dentry with the
file_dentry() accessor, which will always return a native object.

Reported-by: Daniel Axtens <dja@xxxxxxxxxx>
Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Fixes: ff978b09f973 ("ext4 crypto: move context consistency check to ext4_file_open()")
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/ext4/file.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -380,7 +380,7 @@ static int ext4_file_open(struct inode *
 			return -ENOKEY;
 	}
 
-	dir = dget_parent(filp->f_path.dentry);
+	dir = dget_parent(file_dentry(filp));
 	if (ext4_encrypted_inode(d_inode(dir)) &&
 	    !ext4_is_child_context_consistent_with_parent(d_inode(dir), inode)) {
 		ext4_warning(inode->i_sb,