linux/fs/ceph
Kees Cook a068acf2ee fs: create and use seq_show_option for escaping
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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-09-04 16:54:41 -07:00
..
Kconfig ceph: add acl for cephfs 2013-12-31 20:32:01 +02:00
Makefile ceph: add acl for cephfs 2013-12-31 20:32:01 +02:00
acl.c ceph: switch some GFP_NOFS memory allocation to GFP_KERNEL 2015-06-25 11:49:31 +03:00
addr.c ceph: fix ceph_writepages_start() 2015-06-25 18:30:53 +03:00
cache.c ceph: fscache: Wait for completion of object initialization 2014-04-03 10:33:53 +08:00
cache.h ceph: fscache: add an interface to synchronize object store limit 2014-04-03 10:33:53 +08:00
caps.c ceph: always re-send cap flushes when MDS recovers 2015-07-31 11:38:53 +03:00
ceph_frag.c ceph: factor out libceph from Ceph file system 2010-10-20 15:37:28 -07:00
debugfs.c VFS: normal filesystems (and lustre): d_inode() annotations 2015-04-15 15:06:57 -04:00
dir.c ceph: rework dcache readdir 2015-06-25 11:49:32 +03:00
export.c VFS: normal filesystems (and lustre): d_inode() annotations 2015-04-15 15:06:57 -04:00
file.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2015-07-04 19:36:06 -07:00
inode.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client 2015-07-02 11:35:00 -07:00
ioctl.c ceph: fix divide-by-zero in __validate_layout() 2014-10-14 12:57:05 -07:00
ioctl.h ceph: fully initialize new layout 2012-05-16 14:28:27 -05:00
locks.c ceph: fix ceph_encode_locks_to_buffer() 2015-07-31 11:38:47 +03:00
mds_client.c ceph: switch some GFP_NOFS memory allocation to GFP_KERNEL 2015-06-25 11:49:31 +03:00
mds_client.h ceph: rework dcache readdir 2015-06-25 11:49:32 +03:00
mdsmap.c fs/ceph: replace pr_warning by pr_warn 2014-06-06 16:08:06 -07:00
snap.c ceph: make sure syncfs flushes all cap snaps 2015-06-25 11:49:29 +03:00
strings.c ceph: rename snapshot support 2015-04-22 18:33:41 +03:00
super.c fs: create and use seq_show_option for escaping 2015-09-04 16:54:41 -07:00
super.h ceph: always re-send cap flushes when MDS recovers 2015-07-31 11:38:53 +03:00
xattr.c ceph: pre-allocate data structure that tracks caps flushing 2015-06-25 11:49:31 +03:00