linux-kernel - [PATCH 2/2] overlayfs: Fix dentry reference leak

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Message-ID: <20150918104522.7696.6538.stgit@warthog.procyon.org.uk>
Date:	Fri, 18 Sep 2015 11:45:22 +0100
From:	David Howells <dhowells@...hat.com>
To:	miklos@...redi.hu
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	linux-unionfs@...r.kernel.org, viro@...IV.linux.org.uk
Subject: [PATCH 2/2] overlayfs: Fix dentry reference leak

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>
---

 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 89b4cb3773d7..d3a5990fd2b9 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -270,7 +270,7 @@ out:

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

 /*

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