On Tue, Jun 4, 2019 at 9:35 AM David Howells [off-list ref] wrote:

Hi Al,

Here's a set of patches to add a general variable-length notification queue
concept and to add sources of events for:

I asked before and didn't see a response, so I'll ask again.  Why are
you paying any attention at all to the creds that generate an event?
It seems like the resulting security model will be vary hard to
understand and probably buggy.  Can't you define a sensible model in
which only the listener creds matter?

LSM support is included:

 (1) The creds of the process that did the fput() that reduced the refcount
     to zero are cached in the file struct.

 (2) __fput() overrides the current creds with the creds from (1) whilst
     doing the cleanup, thereby making sure that the creds seen by the
     destruction notification generated by mntput() appears to come from
     the last fputter.

That looks like duct tape that is, at best, likely to be very buggy.

 (3) security_post_notification() is called for each queue that we might
     want to post a notification into, thereby allowing the LSM to prevent
     covert communications.

This seems like the wrong approach.  If an LSM wants to prevent covert
communication from, say, mount actions, then it shouldn't allow the
watch to be set up in the first place.