Re: [PATCH] KEYS: fix race between updating and finding negative key

From	David Howells <dhowells@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] KEYS: fix race between updating and finding negative key
Date	2017-09-19 18:30 +0200
Message-ID	<urtzj-7ID-1@gated-at.bofh.it> (permalink)
References	<urbj4-32d-1@gated-at.bofh.it>
Organization	Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903

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Eric Biggers <ebiggers3@gmail.com> wrote:

> Fix the bug by moving ->reject_error out of the union with ->payload,
> then using nonzero ->reject_error to mean that the key is negative.
> 
> This eliminates the need for KEY_FLAG_NEGATIVE, which we remove as well
> so that we don't have to handle memory ordering between
> KEY_FLAG_NEGATIVE and ->reject_error.  We *do* still need to handle
> memory ordering between KEY_FLAG_INSTANTIATED and ->reject_error, but
> that was needed before (and for KEY_FLAG_NEGATIVE as well --- though it
> wasn't done correctly, which was another bug).

Hmmm...  My only objection is that it extends struct key still further, but
you do have a point.

If we're going to do this, can we eliminate KEY_FLAG_INSTANTIATED also and
make ->reject_error into ->status?

	0	-> uninstantiated
	1	-> instantiated
	<0	-> negatively instantiated/rejected

Also, can we make it a short int please?

Also, can setting this field be done with a release barrier rather than a
write barrier?

David

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[PATCH] KEYS: fix race between updating and finding negative key Eric Biggers <ebiggers3@gmail.com> - 2017-09-18 23:00 +0200
  Re: [PATCH] KEYS: fix race between updating and finding negative key David Howells <dhowells@redhat.com> - 2017-09-19 18:30 +0200

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