On Tue, Jan 12, 2021 at 11:00:52PM +0100, Christian Brauner wrote:

In order to determine whether a caller holds privilege over a given
inode the capability framework exposes the two helpers
privileged_wrt_inode_uidgid() and capable_wrt_inode_uidgid(). The former
verifies that the inode has a mapping in the caller's user namespace and
the latter additionally verifies that the caller has the requested
capability in their current user namespace.
If the inode is accessed through an idmapped mount we simply need to map
it according to the mount's user namespace. Afterwards the checks are
identical to non-idmapped inodes. If the initial user namespace is
passed all operations are a nop so non-idmapped mounts will not see a
change in behavior and will also not see any performance impact.

This adds a bunch of pointless > 80 char lines, that would be nice to
fix up.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>