[PATCH v3] virtio-pci: Fix the use of an uninitialized irqfd

[Cindy Lu <lulu@redhat.com>]

The crash was reported in MAC OS and NixOS, here is the link for this bug
https://gitlab.com/qemu-project/qemu/-/issues/2334
https://gitlab.com/qemu-project/qemu/-/issues/2321

The root cause is the function virtio_pci_set_guest_notifiers() was not called
in the virtio_input device.So the vector_irqfd was not initialized

So the fix is add the check for vector_irqfd.

Change in V3
1) Move the vector_irqfd check to virtio_pci_get_notifier().
The function virtio_pci_get_notifier() can also be used while vdev->status
is not VIRTIO_CONFIG_S_DRIVER_OK. In that case, the vector_irqfd could be NULL,
so also add the status check here.
2) Add the return value check for kvm_virtio_pci_vector_use_one().
Since the return value of function virtio_pci_set_vector() is void,
just add the error message here.

This fix is verified in vyatta,MacOS,NixOS,fedora system.

The bt tree for this bug is:
Thread 6 "CPU 0/KVM" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7c817be006c0 (LWP 1269146)]
kvm_virtio_pci_vq_vector_use () at ../qemu-9.0.0/hw/virtio/virtio-pci.c:817
817         if (irqfd->users == 0) {
(gdb) thread apply all bt
...
Thread 6 (Thread 0x7c817be006c0 (LWP 1269146) "CPU 0/KVM"):
0  kvm_virtio_pci_vq_vector_use () at ../qemu-9.0.0/hw/virtio/virtio-pci.c:817
1  kvm_virtio_pci_vector_use_one () at ../qemu-9.0.0/hw/virtio/virtio-pci.c:893
2  0x00005983657045e2 in memory_region_write_accessor () at ../qemu-9.0.0/system/memory.c:497
3  0x0000598365704ba6 in access_with_adjusted_size () at ../qemu-9.0.0/system/memory.c:573
4  0x0000598365705059 in memory_region_dispatch_write () at ../qemu-9.0.0/system/memory.c:1528
5  0x00005983659b8e1f in flatview_write_continue_step.isra.0 () at ../qemu-9.0.0/system/physmem.c:2713
6  0x000059836570ba7d in flatview_write_continue () at ../qemu-9.0.0/system/physmem.c:2743
7  flatview_write () at ../qemu-9.0.0/system/physmem.c:2774
8  0x000059836570bb76 in address_space_write () at ../qemu-9.0.0/system/physmem.c:2894
9  0x0000598365763afe in address_space_rw () at ../qemu-9.0.0/system/physmem.c:2904
10 kvm_cpu_exec () at ../qemu-9.0.0/accel/kvm/kvm-all.c:2917
11 0x000059836576656e in kvm_vcpu_thread_fn () at ../qemu-9.0.0/accel/kvm/kvm-accel-ops.c:50
12 0x0000598365926ca8 in qemu_thread_start () at ../qemu-9.0.0/util/qemu-thread-posix.c:541
13 0x00007c8185bcd1cf in ??? () at /usr/lib/libc.so.6
14 0x00007c8185c4e504 in clone () at /usr/lib/libc.so.6

Fixes: 2ce6cff94d ("virtio-pci: fix use of a released vector")
Cc: qemu-stable@nongnu.org

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 hw/virtio/virtio-pci.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index b1d02f4b3d..87307b9061 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -860,6 +860,11 @@ static int virtio_pci_get_notifier(VirtIOPCIProxy *proxy, int queue_no,
     VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
     VirtQueue *vq;
 
+    if ((proxy->vector_irqfd == NULL) &&
+        (vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
+        return -1;
+    }
+
     if (queue_no == VIRTIO_CONFIG_IRQ_IDX) {
         *n = virtio_config_get_guest_notifier(vdev);
         *vector = vdev->config_vector;
@@ -1452,7 +1457,9 @@ static void virtio_pci_set_vector(VirtIODevice *vdev,
     }
     /* If the new vector changed need to set it up. */
     if (kvm_irqfd && new_vector != VIRTIO_NO_VECTOR) {
-        kvm_virtio_pci_vector_use_one(proxy, queue_no);
+        if (kvm_virtio_pci_vector_use_one(proxy, queue_no)) {
+            virtio_error(vdev, "fail to set the vector %d", new_vector);
+        }
     }
 }
 
-- 
2.45.0