[PATCH v4 00/30] acl: add vfs posix acl api
Christian Brauner
brauner at kernel.org
Thu Sep 29 15:30:10 UTC 2022
From: "Christian Brauner (Microsoft)" <brauner at kernel.org>
Hey everyone,
/* v4 */
Various minor changes. Details in the notes to the commits.
As we discussed and seen multiple times the current state of how posix
acls are handled isn't nice and comes with a lot of problems. For a long
and detailed explanation for just some of the issues [1] provides a good
summary.
The current way of handling posix acls via the generic xattr api is
error prone, hard to maintain, and type unsafe for the vfs until we call
into the filesystem's dedicated get and set inode operations.
It is already the case that posix acls are special-cased to death all
the way through the vfs. There are an uncounted number of hacks that
operate on the uapi posix acl struct instead of the dedicated vfs struct
posix_acl. And the vfs must be involved in order to interpret and fixup
posix acls before storing them to the backing store, caching them,
reporting them to userspace, or for permission checking.
Currently a range of hacks and duct tape exist to make this work. As
with most things this is really no ones fault it's just something that
happened over time. But the code is hard to understand and difficult
to maintain and one is constantly at risk of introducing bugs and
regressions when having to touch it.
Instead of continuing to hack posix acls through the xattr handlers this
series builds a dedicated posix acl api solely around the get and set
inode operations. Going forward, the vfs_get_acl(), vfs_remove_acl(),
and vfs_set_acl() helpers must be used in order to interact with posix
acls. They operate directly on the vfs internal struct posix_acl instead
of abusing the uapi posix acl struct as we currently do. In the end this
removes all of the hackiness, makes the codepaths easier to maintain,
and gets us type safety.
This series passes the LTP and xfstests suites without any regressions.
For xfstests the following combinations were tested:
* xfs
* ext4
* btrfs
* overlayfs
* overlayfs on top of idmapped mounts
For people wanting to run their own xfstests I'd recommend to shorten
their test runs via:
./check -g acl,attr,cap,idmapped,io_uring,perms,subvol,unlink
I would appreciate if the 9p and cifs folks could run any posix acl
related tests as I have no setup to really do this without causing me a
lot of pain.
Very likely there's a lot more simplifications for posix acls that we
can make in the future if the basic api has made it.
A few implementation details:
* The series makes sure to retain exactly the same security and
integrity module permission checks. See [2] for annotated callchains.
Especially for the integrity modules this api is a win because right
now they convert the uapi posix acl struct passed to them via a void
pointer into the vfs struct posix_acl format to perform permission
checking on the mode.
There's a new dedicated security hook for setting posix acls which
passes the vfs struct posix_acl not a void pointer. Basing checking on
the posix acl stored in the uapi format is really unreliable. The vfs
currently hacks around directly in the uapi struct storing values that
frankly the security and integrity modules can't correctly interpret
as evidenced by bugs we reported and fixed in this area. It's not
necessarily even their fault it's just that the format we provide to
them is sub optimal.
* Some filesystems like 9p and cifs need access to the dentry in order
to get and set posix acls which is why they either only partially or
not even at all implement get and set inode operations. For example,
cifs allows setxattr() and getxattr() operations but doesn't allow
permission checking based on posix acls because it can't implement a
get acl inode operation.
Thus, this patch series updates the set acl inode operation to take a
dentry instead of an inode argument. However, for the get acl inode
operation we can't do this as the old get acl method is called in
e.g., generic_permission() and inode_permission(). These helpers in
turn are called in various filesystem's permission inode operation. So
passing a dentry argument to the old get acl inode operation would
amount to passing a dentry to the permission inode operation which we
shouldn't and probably can't do.
So instead of extending the existing inode operation Christoph
suggested to add a new one. He also requested to ensure that the get
and set acl inode operation taking a dentry are consistently named. So
for this version the old get acl operation is renamed to
->get_inode_acl() and a new ->get_acl() inode operation taking a
dentry is added. With this we can give both 9p and cifs get and set
acl inode operations and in turn remove their complex custom posix
xattr handlers.
* I've done a full audit of every codepaths using variant of the
current generic xattr api to get and set posix acls and surprisingly
it isn't that many places. There's of course always a chance that I
might have missed some and I'm sure we'll find them soon enough.
The crucial codepaths to be converted are obviously stacking
filesystems such as ecryptfs and overlayfs.
For a list of all callers currently using generic xattr api helpers
see [2] including comments whether they support posix acls or not.
* The old vfs generic posix acl infrastructure doesn't obey
the create and replace semantics promised on the setxattr(2) manpage.
This patch series doesn't address this. It really is something we
should revisit later though.
The patch series is roughly organized as follows:
// intended to be a non-functional change
1. Change existing set acl inode operation to take a dentry argument.
// intended to be a non-functional change
2. Rename existing get acl method.
// intended to be a non-functional change
3. Implement get and set acl inode operations for filesystems that
couldn't implement one before because of the missing dentry. That's
mostly 9p and cifs.
// intended to be a non-functional change
4. Build posix acl api, i.e., add vfs_get_acl(), vfs_remove_acl(), and
vfs_set_acl() including security and integrity hooks.
// intended to be a non-functional change
5. Implement get and set acl inode operations for stacking filesystems.
// semantical change
6. Switch posix acl handling in stacking filesystems to new posix acl
api now that all filesystems it can stack upon support it.
// semantical change
7. Switch vfs to new posix acl api
8. Remove all now unused helpers
The series can be pulled from:
https://gitlab.com/brauner/linux/-/commits/fs.acl.rework
https://git.kernel.org/pub/scm/linux/kernel/git/vfs/idmapping.git/log/?h=fs.acl.rework
The series contains a few preliminary patches which are scheduled for
the next merge window. It was just easier to base the series on top of
them. But if you pull this branch you'll get them included.
I've been working on this for a while and before going any further it'd
be nice to get some reviews. I think that it should be fine to have get
and set acl inode operations that operate on the dentry at least nothing
stuck out immediately that would prevent this. But obviously having
other people point out issues with that would be helpful.
Thanks to Seth for a lot of good discussion around this and
encouragement and input from Christoph.
[1]: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org
[2]: https://gist.github.com/brauner/12c795b93a05dc3b3056b1982549a633
Thanks!
Christian
/* v1 */
Link: https://lore.kernel.org/linux-cifs/20220922151728.1557914-1-brauner@kernel.org
/* v2 */
Link: https://lore.kernel.org/linux-cifs/20220926140827.142806-1-brauner@kernel.org
This fixes various things pointed out during review. The individual
commits contain more details were appropriate.
/* v3 */
Link: https://lore.kernel.org/linux-cifs/20220928160843.382601-1-brauner@kernel.org
As requested this adds dedicated get and remove security hooks in
addition to the set hook instead of reusing the generic xattr hooks.
Christian Brauner (30):
orangefs: rework posix acl handling when creating new filesystem
objects
fs: pass dentry to set acl method
fs: rename current get acl method
fs: add new get acl method
cifs: implement get acl method
cifs: implement set acl method
9p: implement get acl method
9p: implement set acl method
security: add get, remove and set acl hook
selinux: implement get, set and remove acl hook
smack: implement get, set and remove acl hook
integrity: implement get and set acl hook
evm: add post set acl hook
internal: add may_write_xattr()
acl: add vfs_set_acl()
acl: add vfs_get_acl()
acl: add vfs_remove_acl()
ksmbd: use vfs_remove_acl()
ecryptfs: implement get acl method
ecryptfs: implement set acl method
ovl: implement get acl method
ovl: implement set acl method
ovl: use posix acl api
xattr: use posix acl api
evm: remove evm_xattr_acl_change()
ecryptfs: use stub posix acl handlers
ovl: use stub posix acl handlers
cifs: use stub posix acl handlers
9p: use stub posix acl handlers
acl: remove a slew of now unused helpers
Documentation/filesystems/locking.rst | 4 +-
Documentation/filesystems/porting.rst | 4 +-
Documentation/filesystems/vfs.rst | 3 +-
fs/9p/acl.c | 295 ++++++-----
fs/9p/acl.h | 8 +-
fs/9p/vfs_inode_dotl.c | 4 +
fs/9p/xattr.c | 7 +-
fs/9p/xattr.h | 2 -
fs/bad_inode.c | 4 +-
fs/btrfs/acl.c | 3 +-
fs/btrfs/ctree.h | 2 +-
fs/btrfs/inode.c | 8 +-
fs/ceph/acl.c | 3 +-
fs/ceph/dir.c | 2 +-
fs/ceph/inode.c | 4 +-
fs/ceph/super.h | 2 +-
fs/cifs/cifsacl.c | 141 +++++
fs/cifs/cifsfs.c | 4 +
fs/cifs/cifsproto.h | 20 +-
fs/cifs/cifssmb.c | 206 +++++---
fs/cifs/xattr.c | 68 +--
fs/ecryptfs/inode.c | 32 ++
fs/erofs/inode.c | 6 +-
fs/erofs/namei.c | 2 +-
fs/ext2/acl.c | 3 +-
fs/ext2/acl.h | 2 +-
fs/ext2/file.c | 2 +-
fs/ext2/inode.c | 2 +-
fs/ext2/namei.c | 4 +-
fs/ext4/acl.c | 3 +-
fs/ext4/acl.h | 2 +-
fs/ext4/file.c | 2 +-
fs/ext4/ialloc.c | 2 +-
fs/ext4/inode.c | 2 +-
fs/ext4/namei.c | 4 +-
fs/f2fs/acl.c | 4 +-
fs/f2fs/acl.h | 2 +-
fs/f2fs/file.c | 4 +-
fs/f2fs/namei.c | 4 +-
fs/fuse/acl.c | 3 +-
fs/fuse/dir.c | 4 +-
fs/fuse/fuse_i.h | 2 +-
fs/gfs2/acl.c | 3 +-
fs/gfs2/acl.h | 2 +-
fs/gfs2/inode.c | 6 +-
fs/internal.h | 5 +
fs/jffs2/acl.c | 3 +-
fs/jffs2/acl.h | 2 +-
fs/jffs2/dir.c | 2 +-
fs/jffs2/file.c | 2 +-
fs/jffs2/fs.c | 2 +-
fs/jfs/acl.c | 3 +-
fs/jfs/file.c | 4 +-
fs/jfs/jfs_acl.h | 2 +-
fs/jfs/namei.c | 2 +-
fs/ksmbd/smb2pdu.c | 8 +-
fs/ksmbd/smbacl.c | 6 +-
fs/ksmbd/vfs.c | 21 +-
fs/ksmbd/vfs.h | 4 +-
fs/namei.c | 4 +-
fs/nfs/nfs3_fs.h | 2 +-
fs/nfs/nfs3acl.c | 9 +-
fs/nfs/nfs3proc.c | 4 +-
fs/nfsd/nfs2acl.c | 8 +-
fs/nfsd/nfs3acl.c | 8 +-
fs/nfsd/nfs4acl.c | 4 +-
fs/nfsd/vfs.c | 4 +-
fs/ntfs3/file.c | 4 +-
fs/ntfs3/namei.c | 4 +-
fs/ntfs3/ntfs_fs.h | 4 +-
fs/ntfs3/xattr.c | 9 +-
fs/ocfs2/acl.c | 3 +-
fs/ocfs2/acl.h | 2 +-
fs/ocfs2/file.c | 4 +-
fs/ocfs2/namei.c | 2 +-
fs/orangefs/acl.c | 47 +-
fs/orangefs/inode.c | 47 +-
fs/orangefs/namei.c | 2 +-
fs/orangefs/orangefs-kernel.h | 8 +-
fs/orangefs/orangefs-utils.c | 12 +-
fs/overlayfs/copy_up.c | 38 ++
fs/overlayfs/dir.c | 22 +-
fs/overlayfs/inode.c | 153 +++++-
fs/overlayfs/overlayfs.h | 34 +-
fs/overlayfs/super.c | 107 +---
fs/posix_acl.c | 728 +++++++++++++-------------
fs/reiserfs/acl.h | 6 +-
fs/reiserfs/file.c | 2 +-
fs/reiserfs/inode.c | 2 +-
fs/reiserfs/namei.c | 4 +-
fs/reiserfs/xattr_acl.c | 11 +-
fs/xattr.c | 82 +--
fs/xfs/xfs_acl.c | 3 +-
fs/xfs/xfs_acl.h | 2 +-
fs/xfs/xfs_iops.c | 16 +-
include/linux/evm.h | 49 ++
include/linux/fs.h | 10 +-
include/linux/ima.h | 21 +
include/linux/lsm_hook_defs.h | 6 +
include/linux/lsm_hooks.h | 12 +
include/linux/posix_acl.h | 41 +-
include/linux/posix_acl_xattr.h | 43 +-
include/linux/security.h | 29 +
include/linux/xattr.h | 6 +
mm/shmem.c | 2 +-
security/integrity/evm/evm_main.c | 134 ++---
security/integrity/ima/ima_appraise.c | 9 +
security/security.c | 42 ++
security/selinux/hooks.c | 24 +
security/smack/smack_lsm.c | 69 +++
110 files changed, 1766 insertions(+), 1094 deletions(-)
base-commit: 38e316398e4e6338b80223fb5f74415c0513718f
--
2.34.1
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