[PATCH] virtio-net: fix for heap-buffer-overflow

[Xuan Zhuo]

Run shell script:

    cat << EOF | valgrind qemu-system-i386 -display none -machine accel=qtest, 
-m \
    512M -M q35 -nodefaults -device virtio-net,netdev=net0 -netdev \
    user,id=net0 -qtest stdio
    outl 0xcf8 0x80000810
    outl 0xcfc 0xc000
    outl 0xcf8 0x80000804
    outl 0xcfc 0x01
    outl 0xc00d 0x0200
    outl 0xcf8 0x80000890
    outb 0xcfc 0x4
    outl 0xcf8 0x80000889
    outl 0xcfc 0x1c000000
    outl 0xcf8 0x80000893
    outw 0xcfc 0x100
    EOF

Got:
    ==68666== Invalid read of size 8
    ==68666==    at 0x688536: virtio_net_queue_enable (virtio-net.c:575)
    ==68666==    by 0x6E31AE: memory_region_write_accessor (memory.c:492)
    ==68666==    by 0x6E098D: access_with_adjusted_size (memory.c:554)
    ==68666==    by 0x6E4DB3: memory_region_dispatch_write (memory.c:1521)
    ==68666==    by 0x6E31AE: memory_region_write_accessor (memory.c:492)
    ==68666==    by 0x6E098D: access_with_adjusted_size (memory.c:554)
    ==68666==    by 0x6E4DB3: memory_region_dispatch_write (memory.c:1521)
    ==68666==    by 0x6EBCD3: flatview_write_continue (physmem.c:2820)
    ==68666==    by 0x6EBFBF: flatview_write (physmem.c:2862)
    ==68666==    by 0x6EF5E7: address_space_write (physmem.c:2958)
    ==68666==    by 0x6DFDEC: cpu_outw (ioport.c:70)
    ==68666==    by 0x6F6DF0: qtest_process_command (qtest.c:480)
    ==68666==  Address 0x29087fe8 is 24 bytes after a block of size 416 in 
arena "client"

That is reported by Alexander Bulekov. 
https://gitlab.com/qemu-project/qemu/-/issues/1309

Here, the queue_index is the index of the cvq, but cvq does not have the
corresponding NetClientState, so overflow appears.

I add a check here, ignore illegal queue_index and cvq queue_index.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 hw/net/virtio-net.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 975bbc22f9..88f25709d6 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -549,7 +549,14 @@ static RxFilterInfo 
*virtio_net_query_rxfilter(NetClientState *nc)
 static void virtio_net_queue_reset(VirtIODevice *vdev, uint32_t queue_index)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
-    NetClientState *nc = qemu_get_subqueue(n->nic, vq2q(queue_index));
+    NetClientState *nc;
+
+    /* validate queue_index and skip for cvq */
+    if (queue_index >= n->max_queue_pairs * 2) {
+        return;
+    }
+
+    nc = qemu_get_subqueue(n->nic, vq2q(queue_index));
 
     if (!nc->peer) {
         return;
@@ -566,9 +573,16 @@ static void virtio_net_queue_reset(VirtIODevice *vdev, 
uint32_t queue_index)
 static void virtio_net_queue_enable(VirtIODevice *vdev, uint32_t queue_index)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
-    NetClientState *nc = qemu_get_subqueue(n->nic, vq2q(queue_index));
+    NetClientState *nc;
     int r;
 
+    /* validate queue_index and skip for cvq */
+    if (queue_index >= n->max_queue_pairs * 2) {
+        return;
+    }
+
+    nc = qemu_get_subqueue(n->nic, vq2q(queue_index));
+
     if (!nc->peer || !vdev->vhost_started) {
         return;
     }
-- 
2.32.0.3.g01195cf9f