[PATCH v5 19/42] namei: handle idmapped mounts in may_*() helpers

[Christoph Hellwig]

On Tue, Jan 12, 2021 at 11:01:01PM +0100, Christian Brauner wrote:
> The may_follow_link(), may_linkat(), may_lookup(), may_open(),
> may_o_create(), may_create_in_sticky(), may_delete(), and may_create()
> helpers determine whether the caller is privileged enough to perform the
> associated operations. Let them handle idmapped mounts by mapping the
> inode or fsids according to the mount's user namespace. Afterwards the
> checks are identical to non-idmapped inodes. The patch takes care to
> retrieve the mount's user namespace right before performing permission
> checks and passing it down into the fileystem so the user namespace
> can't change in between by someone idmapping a mount that is currently
> not idmapped. If the initial user namespace is passed nothing changes so
> non-idmapped mounts will see identical behavior as before.

Looks good,

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