[4.2.y-ckt stable] Patch "ovl: fix permission checking for setattr" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ovl: fix permission checking for setattr

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 1d4b187d19b45680018230f393367e5763eca2a4 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <miklos at szeredi.hu>
Date: Fri, 4 Dec 2015 19:18:48 +0100
Subject: ovl: fix permission checking for setattr

commit acff81ec2c79492b180fade3c2894425cd35a545 upstream.

[Al Viro] The bug is in being too enthusiastic about optimizing ->setattr()
away - instead of "copy verbatim with metadata" + "chmod/chown/utimes"
(with the former being always safe and the latter failing in case of
insufficient permissions) it tries to combine these two.  Note that copyup
itself will have to do ->setattr() anyway; _that_ is where the elevated
capabilities are right.  Having these two ->setattr() (one to set verbatim
copy of metadata, another to do what overlayfs ->setattr() had been asked
to do in the first place) combined is where it breaks.

Signed-off-by: Miklos Szeredi <miklos at szeredi.hu>
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/overlayfs/inode.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index ec0c2a0..9612849 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -49,13 +49,13 @@ int ovl_setattr(struct dentry *dentry, struct iattr *attr)
 	if (err)
 		goto out;

-	upperdentry = ovl_dentry_upper(dentry);
-	if (upperdentry) {
+	err = ovl_copy_up(dentry);
+	if (!err) {
+		upperdentry = ovl_dentry_upper(dentry);
+
 		mutex_lock(&upperdentry->d_inode->i_mutex);
 		err = notify_change(upperdentry, attr, NULL);
 		mutex_unlock(&upperdentry->d_inode->i_mutex);
-	} else {
-		err = ovl_copy_up_last(dentry, attr, false);
 	}
 	ovl_drop_write(dentry);
 out:
--
1.9.1