[3.16.y-ckt,stable] Patch "fs: create and use seq_show_option for escaping" has been added to staging queue

From: Kees Cook <keescook@chromium.org>

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

    fs: create and use seq_show_option for escaping

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt18.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

From fc810d109aacb6715a851db5a53374abb3af132a Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Fri, 4 Sep 2015 15:44:57 -0700
Subject: fs: create and use seq_show_option for escaping

commit a068acf2ee77693e0bf39d6e07139ba704f461c3 upstream.

Many file systems that implement the show_options hook fail to correctly
escape their output which could lead to unescaped characters (e.g.  new
lines) leaking into /proc/mounts and /proc/[pid]/mountinfo files.  This
could lead to confusion, spoofed entries (resulting in things like
systemd issuing false d-bus "mount" notifications), and who knows what
else.  This looks like it would only be the root user stepping on
themselves, but it's possible weird things could happen in containers or
in other situations with delegated mount privileges.

Here's an example using overlay with setuid fusermount trusting the
contents of /proc/mounts (via the /etc/mtab symlink).  Imagine the use
of "sudo" is something more sneaky:

  $ BASE="ovl"
  $ MNT="$BASE/mnt"
  $ LOW="$BASE/lower"
  $ UP="$BASE/upper"
  $ WORK="$BASE/work/ 0 0
  none /proc fuse.pwn user_id=1000"
  $ mkdir -p "$LOW" "$UP" "$WORK"
  $ sudo mount -t overlay -o "lowerdir=$LOW,upperdir=$UP,workdir=$WORK" none /mnt
  $ cat /proc/mounts
  none /root/ovl/mnt overlay rw,relatime,lowerdir=ovl/lower,upperdir=ovl/upper,workdir=ovl/work/ 0 0
  none /proc fuse.pwn user_id=1000 0 0
  $ fusermount -u /proc
  $ cat /proc/mounts
  cat: /proc/mounts: No such file or directory

This fixes the problem by adding new seq_show_option and
seq_show_option_n helpers, and updating the vulnerable show_option
handlers to use them as needed.  Some, like SELinux, need to be open
coded due to unusual existing escape mechanisms.

[akpm@linux-foundation.org: add lost chunk, per Kees]
[keescook@chromium.org: seq_show_option should be using const parameters]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Jan Kara <jack@suse.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Cc: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[ luis: backported to 3.16:
  - dropped changes to fs/overlayfs/super.c, net/ceph/ceph_common.c and to
    cgroup_show_options() in kernel/cgroup.c
  - adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 fs/ceph/super.c          |  3 ++-
 fs/cifs/cifsfs.c         |  6 +++---
 fs/ext4/super.c          |  4 ++--
 fs/gfs2/super.c          |  6 +++---
 fs/hfs/super.c           |  4 ++--
 fs/hfsplus/options.c     |  4 ++--
 fs/hostfs/hostfs_kern.c  |  2 +-
 fs/ocfs2/super.c         |  4 ++--
 fs/reiserfs/super.c      |  8 +++++---
 fs/xfs/xfs_super.c       |  4 ++--
 include/linux/seq_file.h | 35 +++++++++++++++++++++++++++++++++++
 kernel/cgroup.c          |  5 +++--
 security/selinux/hooks.c |  2 +-
 13 files changed, 63 insertions(+), 24 deletions(-)

[3.16.y-ckt,stable] Patch "fs: create and use seq_show_option for escaping" has been added to staging queue

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