linux-kernel - Re: [PATCH v3] ipc: introduce ipc_valid_object() helper to sort out IPC

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Date:	Wed, 18 Dec 2013 16:38:24 -0800
From:	Davidlohr Bueso <davidlohr@...com>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Greg Thelen <gthelen@...gle.com>,
	Manfred Spraul <manfred@...orfullife.com>
Subject: Re: [PATCH v3] ipc: introduce ipc_valid_object() helper to sort out
 IPC_RMID races

On Wed, 2013-12-18 at 18:33 -0200, Rafael Aquini wrote:
> After the locking semantics for the SysV IPC API got improved, a couple of
> IPC_RMID race windows were opened because we ended up dropping the
> 'kern_ipc_perm.deleted' check performed way down in ipc_lock().
> The spotted races got sorted out by re-introducing the old test within
> the racy critical sections.
> 
> This patch introduces ipc_valid_object() to consolidate the way we cope with
> IPC_RMID races by using the same abstraction across the API implementation.
> 
> Signed-off-by: Rafael Aquini <aquini@...hat.com>
> Acked-by: Rik van Riel <riel@...hat.com>
> Acked-by: Greg Thelen <gthelen@...gle.com>

Reviewed-by: Davidlohr Bueso <davidlohr@...com>

[...]

> +/*
> + * ipc_valid_object() - helper to sort out IPC_RMID races for codepaths
> + * where the respective ipc_ids.rwsem is not being held down.
> + * Checks whether the ipc object is still around or if it's gone already, as
> + * ipc_rmid() may have already freed the ID while the ipc lock was spinning.
> + * Needs to be called with kern_ipc_perm.lock held -- exception made for one
> + * checkpoint case at sys_semtimedop() as noted in code commentary.
> + */
> +static inline bool ipc_valid_object(struct kern_ipc_perm *perm)
> +{
> +	return perm->deleted == 0;
> +}

I would like to see .deleted being converted to bool while we're at it
though, that return statement just bugs the hell out of me. Could you
send a patch for that as well?

Thanks,
Davidlohr

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