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

[Amit Shah <aams@amazon.com>]

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.

Fixes: 4892c9b4ada9f9 ("xen: add support for MSI message groups")
Reported-by: Hooman Mirhadi <mirhadih@amazon.com>
CC: <stable@vger.kernel.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: Eduardo Valentin <eduval@amazon.com>
CC: Juergen Gross <jgross@suse.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: "K. Y. Srinivasan" <kys@microsoft.com>
CC: Liu Shuo <shuo.a.liu@intel.com>
CC: Anoob Soman <anoob.soman@citrix.com>
Signed-off-by: Amit Shah <aams@amazon.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) {
+		i--;
 		__unbind_from_irq(irq + i);
+	}
 	mutex_unlock(&irq_mapping_update_lock);
 	return ret;
 }
-- 
2.7.3.AMZN

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