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SubjectRe: [RFC][PATCH 00/15] KEYS: Fixes
On Mon, Oct 16, 2017 at 11:27:22PM +0100, David Howells wrote:
> Okay, I've fixed those issues, I think. I've renamed the instantiation labels
> to positive.
>
> Thanks,
> David
> ---
> commit f23f3bb0ba3be44e775ac74148157136b919e3b0
> Author: David Howells <dhowells@redhat.com>
> Date: Wed Oct 4 16:43:25 2017 +0100
>
> KEYS: Fix race between updating and finding a negative key
>
> Consolidate KEY_FLAG_INSTANTIATED, KEY_FLAG_NEGATIVE and the rejection
> error into one field such that:
>
> (1) The instantiation state can be modified/read atomically.
>
> (2) The error can be accessed atomically with the state.
>
> (3) The error isn't stored unioned with the payload pointers.
>
> This deals with the problem that the state is spread over three different
> objects (two bits and a separate variable) and reading or updating them
> atomically isn't practical, given that not only can uninstantiated keys
> change into instantiated or rejected keys, but rejected keys can also turn
> into instantiated keys - and someone accessing the key might not be using
> any locking.
>
> The main side effect of this problem is that what was held in the payload
> may change, depending on the state. For instance, you might observe the
> key to be in the rejected state. You then read the cached error, but if
> the key semaphore wasn't locked, the key might've become instantiated
> between the two reads - and you might now have something in hand that isn't
> actually an error code.
>
> The state is now KEY_IS_UNINSTANTIATED, KEY_IS_POSITIVE or a negative error
> code if the key is negatively instantiated. The key_is_instantiated()
> function is replaced with key_is_positive() to avoid confusion as negative
> keys are also 'instantiated'.
>
> Additionally, barriering is included:
>
> (1) Order payload-set before state-set during instantiation.
>
> (2) Order state-read before payload-read when using the key.
>
> Further separate barriering is necessary if RCU is being used to access the
> payload content after reading the payload pointers.
>
> Fixes: 146aa8b1453b ("KEYS: Merge the type-specific data with the payload data")
> Cc: stable@vger.kernel.org # v4.4+
> Reported-by: Eric Biggers <ebiggers@google.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
>

This looks good now; feel free to add

Reviewed-by: Eric Biggers <ebiggers@google.com>

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