The 3-bit MSI-X BIR fields permit values 0-7, but VFIOPCIDevice::bars[]
only contains BAR0-BAR5 (6 entries). An invalid BIR value of 6 or 7
can cause an out-of-bounds array access (CWE-129) in vfio_msix_early_setup().

Add range checks immediately after extracting the BIR values.

Reported-by: Feifan Qian <bea1e@proton.me>
Fixes: 65501a745dba ("vfio: vfio-pci device assignment driver")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3878
Reviewed-by: Alex Williamson <alex@shazbot.org>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 hw/vfio/pci.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index e6d1adfd3655ce3c1baf8977c82223d23af9b770..c204706e63045c930bda7977adc8034f907b6890 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -1791,6 +1791,14 @@ static bool vfio_msix_early_setup(VFIOPCIDevice *vdev, Error **errp)
     msix->pba_offset = pba & ~PCI_MSIX_FLAGS_BIRMASK;
     msix->entries = (ctrl & PCI_MSIX_FLAGS_QSIZE) + 1;
 
+    if (msix->table_bar >= ARRAY_SIZE(vdev->bars) ||
+        msix->pba_bar >= ARRAY_SIZE(vdev->bars)) {
+        error_setg(errp, "invalid MSI-X BIR, table_bar=%d pba_bar=%d",
+                   msix->table_bar, msix->pba_bar);
+        g_free(msix);
+        return false;
+    }
+
     ret = vfio_device_get_irq_info(&vdev->vbasedev, VFIO_PCI_MSIX_IRQ_INDEX,
                                    &irq_info);
     if (ret < 0) {
-- 
2.54.0