linux-kernel - Re: [PATCH v2 1/2] xen: fix out-of-bounds irq unbind for MSI message groups

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Date:   Tue, 27 Feb 2018 16:58:10 +0000
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Amit Shah <aams@...zon.com>
CC:     <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Liu Shuo <shuo.a.liu@...el.com>,
        Anoob Soman <anoob.soman@...rix.com>
Subject: Re: [PATCH v2 1/2] xen: fix out-of-bounds irq unbind for MSI message
 groups

On Tue, Feb 27, 2018 at 03:55:57PM +0000, Amit Shah wrote:
> When an MSI descriptor was not available, the error path would try to
> unbind an irq that was never acquired - potentially unbinding an
> unrelated irq.

Those IRQs have been allocated in the xen_allocate_irqs_dynamic call,
so I think the "potentially unbinding an unrelated irq" part is wrong.
The unbind call would be performed against an unbound IRQ, which is
harmless AFAICT.

> Fixes: 4892c9b4ada9f9 ("xen: add support for MSI message groups")
> Reported-by: Hooman Mirhadi <mirhadih@...zon.com>
> CC: <stable@...r.kernel.org>
> CC: Roger Pau Monné <roger.pau@...rix.com>
> CC: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> CC: Eduardo Valentin <eduval@...zon.com>
> CC: Juergen Gross <jgross@...e.com>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: "K. Y. Srinivasan" <kys@...rosoft.com>
> CC: Liu Shuo <shuo.a.liu@...el.com>
> CC: Anoob Soman <anoob.soman@...rix.com>
> Signed-off-by: Amit Shah <aams@...zon.com>
> ---
>  drivers/xen/events/events_base.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index 1ab4bd1..c86d10e 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -755,8 +755,10 @@ int xen_bind_pirq_msi_to_irq(struct pci_dev *dev, struct msi_desc *msidesc,
>  	mutex_unlock(&irq_mapping_update_lock);
>  	return irq;
>  error_irq:
> -	for (; i >= 0; i--)
> +	while (i > 0) {

while (i--)
	__unbind_from_irq(irq + i);

Although please see reply to patch 2.

Roger.