linux-kernel - [PATCH 3.19.y-ckt 139/155] ovl: fix dentry reference leak

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Message-Id: <1447370309-357-140-git-send-email-kamal@canonical.com>
Date:	Thu, 12 Nov 2015 15:18:13 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	David Howells <dhowells@...hat.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 139/155] ovl: fix dentry reference leak

3.19.8-ckt10 -stable review patch.  If anyone has any objections, please let me know.

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

From: David Howells <dhowells@...hat.com>

commit ab79efab0a0ba01a74df782eb7fa44b044dae8b5 upstream.

In ovl_copy_up_locked(), newdentry is leaked if the function exits through
out_cleanup as this just to out after calling ovl_cleanup() - which doesn't
actually release the ref on newdentry.

The out_cleanup segment should instead exit through out2 as certainly
newdentry leaks - and possibly upper does also, though this isn't caught
given the catch of newdentry.

Without this fix, something like the following is seen:

	BUG: Dentry ffff880023e9eb20{i=f861,n=#ffff880023e82d90} still in use (1) [unmount of tmpfs tmpfs]
	BUG: Dentry ffff880023ece640{i=0,n=bigfile}  still in use (1) [unmount of tmpfs tmpfs]

when unmounting the upper layer after an error occurred in copyup.

An error can be induced by creating a big file in a lower layer with
something like:

	dd if=/dev/zero of=/lower/a/bigfile bs=65536 count=1 seek=$((0xf000))

to create a large file (4.1G).  Overlay an upper layer that is too small
(on tmpfs might do) and then induce a copy up by opening it writably.

Reported-by: Ulrich Obergfell <uobergfe@...hat.com>
Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Miklos Szeredi <miklos@...redi.hu>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 fs/overlayfs/copy_up.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 94edf78..319c487 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -268,7 +268,7 @@ out:

 out_cleanup:
 	ovl_cleanup(wdir, newdentry);
-	goto out;
+	goto out2;
 }

 /*
-- 
1.9.1

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