[PATCH] virtio: clean up when virtio_queue_set_rings() fails

[Stefan Hajnoczi]

hw/virtio.c checks vq->vring.desc != NULL to see if the vring has been
set up successfully.

When virtio_queue_set_rings() fails due to an invalid vring memory
address it must clear vq->vring.desc (and related fields) so we don't
treat this virtqueue as successfully initialized later on.

This bug was found by device fuzzing and can be triggered as follows:

  $ qemu -M pc -device virtio-blk-pci,id=drv0,drive=drive0,addr=4.0 \
         -drive if=none,id=drive0,file=null-co://,format=raw,auto-read-only=off 
\
         -drive 
if=none,id=drive1,file=null-co://,file.read-zeroes=on,format=raw \
         -display none \
         -qtest stdio
  endianness
  outl 0xcf8 0x80002020
  outl 0xcfc 0xe0000000
  outl 0xcf8 0x80002004
  outw 0xcfc 0x7
  write 0xe0000000 0x24 
0x00ffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffab5cffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffab0000000001
  inb 0x4
  writew 0xe000001c 0x1
  write 0xe0000014 0x1 0x0d

The following error message is produced:

  qemu-system-x86_64: /home/stefanha/qemu/hw/virtio/virtio.c:286: 
vring_get_region_caches: Assertion `caches != NULL' failed.

The backtrace looks like this:

  #0  0x00007ffff5520625 in raise () at /lib64/libc.so.6
  #1  0x00007ffff55098d9 in abort () at /lib64/libc.so.6
  #2  0x00007ffff55097a9 in _nl_load_domain.cold () at /lib64/libc.so.6
  #3  0x00007ffff5518a66 in annobin_assert.c_end () at /lib64/libc.so.6
  #4  0x00005555559073da in vring_get_region_caches (vq=<optimized out>) at 
qemu/hw/virtio/virtio.c:286
  #5  vring_get_region_caches (vq=<optimized out>) at 
qemu/hw/virtio/virtio.c:283
  #6  0x000055555590818d in vring_used_flags_set_bit (mask=1, 
vq=0x5555575ceea0) at qemu/hw/virtio/virtio.c:398
  #7  virtio_queue_split_set_notification (enable=0, vq=0x5555575ceea0) at 
qemu/hw/virtio/virtio.c:398
  #8  virtio_queue_set_notification (vq=vq@entry=0x5555575ceea0, 
enable=enable@entry=0) at qemu/hw/virtio/virtio.c:451
  #9  0x0000555555908512 in virtio_queue_set_notification 
(vq=vq@entry=0x5555575ceea0, enable=enable@entry=0) at 
qemu/hw/virtio/virtio.c:444
  #10 0x00005555558c697a in virtio_blk_handle_vq (s=0x5555575c57e0, 
vq=0x5555575ceea0) at qemu/hw/block/virtio-blk.c:775
  #11 0x0000555555907836 in virtio_queue_notify_aio_vq (vq=0x5555575ceea0) at 
qemu/hw/virtio/virtio.c:2244
  #12 0x0000555555cb5dd7 in aio_dispatch_handlers 
(ctx=ctx@entry=0x55555671a420) at util/aio-posix.c:429
  #13 0x0000555555cb67a8 in aio_dispatch (ctx=0x55555671a420) at 
util/aio-posix.c:460
  #14 0x0000555555cb307e in aio_ctx_dispatch (source=<optimized out>, 
callback=<optimized out>, user_data=<optimized out>) at util/async.c:260
  #15 0x00007ffff7bbc510 in g_main_context_dispatch () at 
/lib64/libglib-2.0.so.0
  #16 0x0000555555cb5848 in glib_pollfds_poll () at util/main-loop.c:219
  #17 os_host_main_loop_wait (timeout=<optimized out>) at util/main-loop.c:242
  #18 main_loop_wait (nonblocking=<optimized out>) at util/main-loop.c:518
  #19 0x00005555559b20c9 in main_loop () at vl.c:1683
  #20 0x0000555555838115 in main (argc=<optimized out>, argv=<optimized out>, 
envp=<optimized out>) at vl.c:4441

Reported-by: Alexander Bulekov <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 hw/virtio/virtio.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 2c5410e981..5d7f619a1e 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2163,6 +2163,11 @@ void virtio_queue_set_rings(VirtIODevice *vdev, int n, 
hwaddr desc,
     vdev->vq[n].vring.avail = avail;
     vdev->vq[n].vring.used = used;
     virtio_init_region_cache(vdev, n);
+    if (vdev->broken) {
+        vdev->vq[n].vring.desc = 0;
+        vdev->vq[n].vring.avail = 0;
+        vdev->vq[n].vring.used = 0;
+    }
 }
 
 void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
-- 
2.24.1