From 5ea5880764cbb164afb17a62e76ca75dc371409d Mon Sep 17 00:00:00 2001
From: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
Date: Fri, 17 Apr 2026 14:27:56 -0600
Subject: vfio/cdx: Fix NULL pointer dereference in interrupt trigger path

From: Prasanna Kumar T S M <ptsm@linux.microsoft.com>

commit 5ea5880764cbb164afb17a62e76ca75dc371409d upstream.

Add validation to ensure MSI is configured before accessing cdx_irqs
array in vfio_cdx_set_msi_trigger(). Without this check, userspace
can trigger a NULL pointer dereference by calling VFIO_DEVICE_SET_IRQS
with VFIO_IRQ_SET_DATA_BOOL or VFIO_IRQ_SET_DATA_NONE flags before
ever setting up interrupts via VFIO_IRQ_SET_DATA_EVENTFD.

The vfio_cdx_msi_enable() function allocates the cdx_irqs array and
sets config_msi to 1 only when called through the EVENTFD path. The
trigger loop (for DATA_BOOL/DATA_NONE) assumed this had already been
done, but there was no enforcement of this call ordering.

This matches the protection used in the PCI VFIO driver where
vfio_pci_set_msi_trigger() checks irq_is() before the trigger loop.

Fixes: 848e447e000c ("vfio/cdx: add interrupt support")
Cc: stable@vger.kernel.org
Signed-off-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
Acked-by: Nipun Gupta <nipun.gupta@amd.com>
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
Acked-by: Nikhil Agarwal <nikhil.agarwal@amd.com>
Link: https://lore.kernel.org/r/20260417202800.88287-2-alex.williamson@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/vfio/cdx/intr.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/vfio/cdx/intr.c
+++ b/drivers/vfio/cdx/intr.c
@@ -177,6 +177,10 @@ static int vfio_cdx_set_msi_trigger(stru
 		return ret;
 	}
 
+	/* Ensure MSI is configured before accessing cdx_irqs */
+	if (!vdev->config_msi)
+		return -EINVAL;
+
 	for (i = start; i < start + count; i++) {
 		if (!vdev->cdx_irqs[i].trigger)
 			continue;