Patch "ext4: use dget_parent() in ext4_file_open()" has been added to the 4.5-stable tree

This is a note to let you know that I've just added the patch titled

ext4: use dget_parent() in ext4_file_open()

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-use-dget_parent-in-ext4_file_open.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Miklos Szeredi <[email protected]>
Date: Sat, 26 Mar 2016 16:14:41 -0400
Subject: ext4: use dget_parent() in ext4_file_open()

From: Miklos Szeredi <[email protected]>

commit 9dd78d8c9a7bd4bc341f5864db32d4331b8eae4c upstream.

In f_op->open() lock on parent is not held, so there's no guarantee that parent dentry won't go away at any time.

Even after this patch there's no guarantee that 'dir' will stay the parent of 'inode', but at least it won't be freed while being used.

---
 fs/ext4/file.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

@@ -335,7 +335,7 @@ static int ext4_file_open(struct inode *
 	struct super_block *sb = inode->i_sb;
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 	struct vfsmount *mnt = filp->f_path.mnt;
-	struct inode *dir = filp->f_path.dentry->d_parent->d_inode;
+	struct dentry *dir;
 	struct path path;
 	char buf[64], *cp;
 	int ret;

@@ -379,14 +379,18 @@ static int ext4_file_open(struct inode *
 		if (ext4_encryption_info(inode) == NULL)
 			return -ENOKEY;
 	}
-	if (ext4_encrypted_inode(dir) &&
-	    !ext4_is_child_context_consistent_with_parent(dir, inode)) {
+
+	dir = dget_parent(filp->f_path.dentry);
+	if (ext4_encrypted_inode(d_inode(dir)) &&
+	    !ext4_is_child_context_consistent_with_parent(d_inode(dir), inode)) {
 		ext4_warning(inode->i_sb,
 			     "Inconsistent encryption contexts: %lu/%lu\n",
-			     (unsigned long) dir->i_ino,
+			     (unsigned long) d_inode(dir)->i_ino,
 			     (unsigned long) inode->i_ino);
+		dput(dir);
 		return -EPERM;
 	}
+	dput(dir);
 	/*
 	 * Set up the jbd2_inode if we are opening the inode for
 	 * writing and the journal is present

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/ext4-use-dget_parent-in-ext4_file_open.patch queue-4.5/ext4-use-file_dentry.patch queue-4.5/nfs-use-file_dentry.patch queue-4.5/fs-add-file_dentry.patch