On 15/05/2023 17:12, Christian Brauner wrote:
On Fri, May 05, 2023 at 04:11:58PM +0800, Xiu Jianfeng wrote:
Hi,
I am working on adding xattr/attr support for landlock [1], so we can
control fs accesses such as chmod, chown, uptimes, setxattr, etc.. inside
landlock sandbox. the LSM hooks as following are invoved:
1.inode_setattr
2.inode_setxattr
3.inode_removexattr
4.inode_set_acl
5.inode_remove_acl
which are controlled by LANDLOCK_ACCESS_FS_WRITE_METADATA.
and
1.inode_getattr
2.inode_get_acl
3.inode_getxattr
4.inode_listxattr
which are controlled by LANDLOCK_ACCESS_FS_READ_METADATA
It would be helpful to get the complete, full picture.
Piecemeal extending vfs helpers with struct path arguments is costly,
will cause a lot of churn and will require a lot of review time from us.
Please give us the list of all security hooks to which you want to pass
a struct path (if there are more to come apart from the ones listed
here). Then please follow all callchains and identify the vfs helpers
that would need to be updated. Then please figure out where those
vfs helpers are called from and follow all callchains finding all
inode_operations that would have to be updated and passed a struct path
argument. So ultimately we'll end up with a list of vfs helpers and
inode_operations that would have to be changed.
I'm very reluctant to see anything merged without knowing _exactly_ what
you're getting us into.
Ultimately we'd like the path-based LSMs to reach parity with the
inode-based LSMs. This proposal's goal is to provide users the ability
to control (in a complete and easy way) file metadata access. For these
we need to extend the inode_*attr hooks and inode_*acl hooks to handle
paths. The chown/chmod hooks are already good.
In the future, I'd also like to be able to control directory traversals
(e.g. chdir), which currently only calls inode_permission().
What would be the best way to reach this goal?
