On Wed, Feb 21, 2024 at 03:24:38PM -0600, Seth Forshee (DigitalOcean) wrote:

cap_inode_getsecurity() implements a handful of policies for capability
xattrs read by userspace:

 - It returns EINVAL if the on-disk capability is in v1 format.

 - It masks off all bits in magic_etc except for the version and
   VFS_CAP_FLAGS_EFFECTIVE.

 - v3 capabilities are converted to v2 format if the rootid returned to
   userspace would be 0 or if the rootid corresponds to root in an
   ancestor user namespace.

 - It returns EOVERFLOW for a v3 capability whose rootid does not map to
   a valid id in current_user_ns() or to root in an ancestor namespace.

These policies must be maintained when converting vfs_caps to an xattr
for userspace. Provide a vfs_caps_to_user_xattr() helper which will
enforce these policies.

Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
---

Looks good,
Reviewed-by: Christian Brauner <brauner@kernel.org>