linux-kernel - Re: [PATCH v2 1/6] KEYS: fix race between updating and finding negative key

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Message-ID: <20170926203909.GA126069@gmail.com>
Date:   Tue, 26 Sep 2017 13:39:09 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     keyrings@...r.kernel.org
Cc:     David Howells <dhowells@...hat.com>,
        Michael Halcrow <mhalcrow@...gle.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 1/6] KEYS: fix race between updating and finding
 negative key

On Tue, Sep 26, 2017 at 01:11:00PM -0700, Eric Biggers wrote:
> +static void mark_key_instantiated(struct key *key, unsigned int reject_error)
> +{
> +	unsigned long old, new;
> +
> +	do {
> +		old = READ_ONCE(key->flags);
> +		new = (old & ~(KEY_FLAG_NEGATIVE |
> +			       KEY_FLAGS_REJECT_ERROR_MASK)) |
> +		      KEY_FLAG_INSTANTIATED |
> +		      (reject_error ? KEY_FLAG_NEGATIVE : 0) |
> +		      (reject_error << KEY_FLAGS_REJECT_ERROR_SHIFT);
> +	} while (cmpxchg_release(&key->flags, old, new) != old);
> +}

Sorry, I realized I screwed this up --- the flags like KEY_FLAG_NEGATIVE need to
be (1 << KEY_FLAG_NEGATIVE).  I'll send another version which will be better
tested...

Eric