[PATCH v14 0/5] overlayfs override_creds=off & nested get xattr fix

[Mark Salyzyn <salyzyn@android.com>]

Patch series:

Mark Salyzyn (5):
  Add flags option to get xattr method paired to __vfs_getxattr
  overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh
  overlayfs: handle XATTR_NOSECURITY flag for get xattr method
  overlayfs: internal getxattr operations without sepolicy checking
  overlayfs: override_creds=off option bypass creator_cred

The first four patches address fundamental security issues that should
be solved regardless of the override_creds=off feature.

The fifth adds the feature depends on these other fixes.

By default, all access to the upper, lower and work directories is the
recorded mounter's MAC and DAC credentials.  The incoming accesses are
checked against the caller's credentials.

If the principles of least privilege are applied for sepolicy, the
mounter's credentials might not overlap the credentials of the caller's
when accessing the overlayfs filesystem.  For example, a file that a
lower DAC privileged caller can execute, is MAC denied to the
generally higher DAC privileged mounter, to prevent an attack vector.

We add the option to turn off override_creds in the mount options; all
subsequent operations after mount on the filesystem will be only the
caller's credentials.  The module boolean parameter and mount option
override_creds is also added as a presence check for this "feature",
existence of /sys/module/overlay/parameters/overlay_creds

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: linux-unionfs@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

---
v14:
- Rejoin, rebase and a few adjustments.

v13:
- Pull out first patch and try to get it in alone feedback, some
  Acks, and then <crickets> because people forgot why we were doing i.

v12:
- Restore squished out patch 2 and 3 in the series,
  then change algorithm to add flags argument.
  Per-thread flag is a large security surface.

v11:
- Squish out v10 introduced patch 2 and 3 in the series,
  then and use per-thread flag instead for nesting.
- Switch name to ovl_do_vds_getxattr for __vds_getxattr wrapper.
- Add sb argument to ovl_revert_creds to match future work.

v10:
- Return NULL on CAP_DAC_READ_SEARCH
- Add __get xattr method to solve sepolicy logging issue
- Drop unnecessary sys_admin sepolicy checking for administrative
  driver internal xattr functions.

v6:
- Drop CONFIG_OVERLAY_FS_OVERRIDE_CREDS.
- Do better with the documentation, drop rationalizations.
- pr_warn message adjusted to report consequences.

v5:
- beefed up the caveats in the Documentation
- Is dependent on
  "overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh"
  "overlayfs: check CAP_MKNOD before issuing vfs_whiteout"
- Added prwarn when override_creds=off

v4:
- spelling and grammar errors in text

v3:
- Change name from caller_credentials / creator_credentials to the
  boolean override_creds.
- Changed from creator to mounter credentials.
- Updated and fortified the documentation.
- Added CONFIG_OVERLAY_FS_OVERRIDE_CREDS

v2:
- Forward port changed attr to stat, resulting in a build error.
- altered commit message.


 Documentation/filesystems/locking.rst   |  10 +--
 Documentation/filesystems/overlayfs.txt |  23 +++++
 fs/9p/acl.c                             |  51 ++++++-----
 fs/9p/xattr.c                           |  19 ++--
 fs/afs/xattr.c                          | 112 +++++++++++-------------
 fs/btrfs/xattr.c                        |  36 ++++----
 fs/ceph/xattr.c                         |  17 ++--
 fs/cifs/xattr.c                         |  72 +++++++--------
 fs/ecryptfs/crypto.c                    |  20 +++--
 fs/ecryptfs/inode.c                     |  36 +++++---
 fs/ecryptfs/mmap.c                      |  39 +++++----
 fs/erofs/xattr.c                        |   8 +-
 fs/ext2/xattr_security.c                |  16 ++--
 fs/ext2/xattr_trusted.c                 |  15 ++--
 fs/ext2/xattr_user.c                    |  19 ++--
 fs/ext4/xattr_security.c                |  15 ++--
 fs/ext4/xattr_trusted.c                 |  15 ++--
 fs/ext4/xattr_user.c                    |  19 ++--
 fs/f2fs/xattr.c                         |  42 ++++-----
 fs/fuse/xattr.c                         |  23 ++---
 fs/gfs2/xattr.c                         |  18 ++--
 fs/hfs/attr.c                           |  15 ++--
 fs/hfsplus/xattr.c                      |  17 ++--
 fs/hfsplus/xattr_security.c             |  13 ++-
 fs/hfsplus/xattr_trusted.c              |  13 ++-
 fs/hfsplus/xattr_user.c                 |  13 ++-
 fs/jffs2/security.c                     |  16 ++--
 fs/jffs2/xattr_trusted.c                |  16 ++--
 fs/jffs2/xattr_user.c                   |  16 ++--
 fs/jfs/xattr.c                          |  33 ++++---
 fs/kernfs/inode.c                       |  23 +++--
 fs/nfs/nfs4proc.c                       |  28 +++---
 fs/ocfs2/xattr.c                        |  52 +++++------
 fs/orangefs/xattr.c                     |  19 ++--
 fs/overlayfs/copy_up.c                  |   2 +-
 fs/overlayfs/dir.c                      |  17 ++--
 fs/overlayfs/file.c                     |  20 ++---
 fs/overlayfs/inode.c                    |  66 +++++++-------
 fs/overlayfs/namei.c                    |  21 +++--
 fs/overlayfs/overlayfs.h                |   9 +-
 fs/overlayfs/ovl_entry.h                |   1 +
 fs/overlayfs/readdir.c                  |   4 +-
 fs/overlayfs/super.c                    |  75 +++++++++-------
 fs/overlayfs/util.c                     |  44 +++++++---
 fs/posix_acl.c                          |  23 +++--
 fs/reiserfs/xattr.c                     |   2 +-
 fs/reiserfs/xattr_security.c            |  22 +++--
 fs/reiserfs/xattr_trusted.c             |  22 +++--
 fs/reiserfs/xattr_user.c                |  22 +++--
 fs/squashfs/xattr.c                     |  10 +--
 fs/ubifs/xattr.c                        |  33 ++++---
 fs/xattr.c                              | 112 +++++++++++++++---------
 fs/xfs/libxfs/xfs_attr.c                |   4 +-
 fs/xfs/libxfs/xfs_attr.h                |   2 +-
 fs/xfs/xfs_xattr.c                      |  35 ++++----
 include/linux/xattr.h                   |  26 ++++--
 include/uapi/linux/xattr.h              |   7 +-
 mm/shmem.c                              |  21 +++--
 net/socket.c                            |  16 ++--
 security/commoncap.c                    |  29 ++++--
 security/integrity/evm/evm_main.c       |  13 ++-
 security/selinux/hooks.c                |  28 ++++--
 security/smack/smack_lsm.c              |  38 +++++---
 63 files changed, 852 insertions(+), 771 deletions(-)

-- 
2.23.0.866.gb869b98d4c-goog