linux-kernel - [PATCH 0/1] OverlayFS: Fix checking permissions during lookup.

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Message-ID: <20160125161052.GA13589@zenon.in.qult.net>
Date:	Mon, 25 Jan 2016 17:10:52 +0100
From:	Ignacy Gawędzki 
	<ignacy.gawedzki@...en-communications.fr>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH 0/1] OverlayFS: Fix checking permissions during lookup.

Hi,

While trying to figure out what exactly is going on with permission
checking in OverlayFS, I found a pretty simple way to, so it seems,
fix it.

The problem I was having is triggered with the following setup:

  drwxr-xr-x lower/
  drwx------ lower/foo/
  drw-r--r-- lower/boo/bar
  drwxr-xr-x upper/
  drwxr-xr-x upper/foo/

mounted with lower/ as the lowerdir and upper/ as the upperdir.

The issue is that when caches are empty, any user who is not the
owner of lower/foo/ and who tries to access foo/bar on the mounted
overlay gets EACCES.  Once the owner accesses foo/bar, that positive
result it cached and other users can access foo/bar as expected.

It would be nice if someone could take a look at the patch that
follows and give me some feedback.  The fix is simple, but a bit
intrusive and I wonder whether this is necessarily the way to go.

Cheers,

Ignacy

Ignacy Gawędzki (1):
  OverlayFS: Fix checking permissions during lookup.

 fs/namei.c            | 21 ++++++++++++++++++++-
 fs/overlayfs/super.c  |  2 +-
 include/linux/namei.h |  1 +
 3 files changed, 22 insertions(+), 2 deletions(-)

-- 
2.5.0