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

[Cornelia Huck <cohuck@redhat.com>]

On Tue,  4 Feb 2020 15:16:18 +0000
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> 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 <alxndr@bu.edu>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  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)

This looks correct; but shouldn't virtio_queue_set_addr() also set
.desc to 0 on failure?