linux-kernel - opening a file on a stacked overlayfs is broken.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20161125145604.GG6842@chrystal.oracle.com>
Date:   Fri, 25 Nov 2016 15:56:04 +0100
From:   Quentin Casasnovas <quentin.casasnovas@...cle.com>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: opening a file on a stacked overlayfs is broken.

Hi,

Stacking an overlayfs on top of an overlayfs doens't work when it used to
(tested on v4.9-rc5):

  #!/bin/bash -xeu
  tmpdir=$(mktemp -d)
  pushd ${tmpdir}

  mkdir -p {upper,lower,work}
  echo 'foo' > lower/bar
  mount -t overlay level_zero upper -o lowerdir=lower,upperdir=upper,workdir=work
  cat upper/bar

  tmpdir2=$(mktemp -d)
  pushd ${tmpdir2}

  mkdir -p {upper,work}
  mount -t overlay level_one upper -o lowerdir=${tmpdir}/upper,upperdir=upper,workdir=work
  stat upper/bar  # Works fine
  cat upper/bar   # open() returns ENXIO

I _think_ (I haven't bisected it) the guilty commit is 2d902671ce1c ("vfs:
merge .d_select_inode() into .d_real()"), where vfs_open() -> uses d_real()
with a a NULL inode, which prevents any recursion from happening, when
before d_select_inode() would do the right thing and recurse.

It should be noted this has already been broken and fixed in the past year
in 1c8a47df36d7 ("ovl: fix open in stacked overlay").

Let me know if I can help,
Q

Download attachment "signature.asc" of type "application/pgp-signature" (802 bytes)