vfio/cdx: Fix NULL pointer dereference in interrupt trigger path

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: 848e447 ("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>

Author: Prasanna Kumar T S M

drivers/vfio/cdx/intr.c

@@ -175,6 +175,10 @@ static int vfio_cdx_set_msi_trigger(struct vfio_cdx_device *vdev,
 		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;