[0/8] introduce dedicated type for idmapped mounts

Message

Christian Brauner June 20, 2022, 1:49 p.m. UTC

From: "Christian Brauner (Microsoft)" <[e-mail]>

Hey everyone,

This series starts to introduce a new kmnt{g,u}id_t type. It allows to
distinguish {g,u}ids on idmapped mounts from filesystem k{g,u}ids.

We leverage the type framework to increase the safety for filesystems
and the vfs when dealing with idmapped mounts.

The series introduces the type and converts the setattr codepaths to
use the new type and associated helpers.

Currently these codepaths place the value that will ultimately be
written to inode->i_{g,u}id into attr->ia_{g,u}id which allows to avoid
changing a few callsites. But there are drawbacks to this approach.

As Linus rightly points out it makes some of the permission checks in
the attribute code harder to understand than they need and should be and
increases the probability for further issues.

This series makes it so that the values will always be treated as being
mapped into the idmapped mount. Only when the filesystem object is
actually updated will the value be mapped into the filesystem idmapping.

I first looked into this about ~7 months ago but put it on hold to focus
on the testsuite. Linus expressed the desire for something like this
last week so I got back to working on this.

Ideally I'd like to get at least this first series in for v5.20. The
conversion can the continue until we can remove all the regular non-type
safe helpers and will only be left with the type safe helpers.

Thanks!
Christian

Christian Brauner (8):
  mnt_idmapping: add kmnt{g,u}id_t
  fs: add two type safe mapping helpers
  fs: use mount types in iattr
  fs: introduce tiny iattr ownership update helpers
  fs: port to iattr ownership update helpers
  quota: port quota helpers mount ids
  security: pass down mount idmapping to setattr hook
  attr: port attribute changes to new types

 fs/attr.c                         |  69 +++++------
 fs/ext2/inode.c                   |   8 +-
 fs/ext4/inode.c                   |  14 +--
 fs/f2fs/file.c                    |  22 ++--
 fs/f2fs/recovery.c                |   2 +-
 fs/fat/file.c                     |   7 +-
 fs/jfs/file.c                     |   4 +-
 fs/ocfs2/file.c                   |   2 +-
 fs/open.c                         |  65 +++++++---
 fs/overlayfs/copy_up.c            |   4 +-
 fs/overlayfs/overlayfs.h          |  12 +-
 fs/quota/dquot.c                  |  17 ++-
 fs/reiserfs/inode.c               |   4 +-
 fs/xfs/xfs_iops.c                 |  11 +-
 fs/zonefs/super.c                 |   2 +-
 include/linux/evm.h               |   6 +-
 include/linux/fs.h                | 135 ++++++++++++++++++++-
 include/linux/mnt_idmapping.h     | 195 ++++++++++++++++++++++++++++++
 include/linux/quotaops.h          |  15 ++-
 include/linux/security.h          |   8 +-
 security/integrity/evm/evm_main.c |  12 +-
 security/security.c               |   5 +-
 22 files changed, 488 insertions(+), 131 deletions(-)


base-commit: a111daf0c53ae91e71fd2bfe7497862d14132e3e