Re: [PATCH] vhost: validate range size before adding to iotlb

[Jason Wang <jasowang@redhat.com>]

On Tue, Feb 22, 2022 at 3:53 AM Anirudh Rayabharam <mail@anirudhrb.com> wrote:
>
> In vhost_iotlb_add_range_ctx(), validate the range size is non-zero
> before proceeding with adding it to the iotlb.
>
> Range size can overflow to 0 when start is 0 and last is (2^64 - 1).
> One instance where it can happen is when userspace sends an IOTLB
> message with iova=size=uaddr=0 (vhost_process_iotlb_msg). So, an
> entry with size = 0, start = 0, last = (2^64 - 1) ends up in the
> iotlb. Next time a packet is sent, iotlb_access_ok() loops
> indefinitely due to that erroneous entry:
>
>         Call Trace:
>          <TASK>
>          iotlb_access_ok+0x21b/0x3e0 drivers/vhost/vhost.c:1340
>          vq_meta_prefetch+0xbc/0x280 drivers/vhost/vhost.c:1366
>          vhost_transport_do_send_pkt+0xe0/0xfd0 drivers/vhost/vsock.c:104
>          vhost_worker+0x23d/0x3d0 drivers/vhost/vhost.c:372
>          kthread+0x2e9/0x3a0 kernel/kthread.c:377
>          ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>          </TASK>
>
> Reported by syzbot at:
>         https://syzkaller.appspot.com/bug?extid=0abd373e2e50d704db87
>
> Reported-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
> Tested-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
> Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
> ---
>  drivers/vhost/iotlb.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vhost/iotlb.c b/drivers/vhost/iotlb.c
> index 670d56c879e5..b9de74bd2f9c 100644
> --- a/drivers/vhost/iotlb.c
> +++ b/drivers/vhost/iotlb.c
> @@ -53,8 +53,10 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb,
>                               void *opaque)
>  {
>         struct vhost_iotlb_map *map;
> +       u64 size = last - start + 1;
>
> -       if (last < start)
> +       // size can overflow to 0 when start is 0 and last is (2^64 - 1).
> +       if (last < start || size == 0)
>                 return -EFAULT;

I'd move this check to vhost_chr_iter_write(), then for the device who
has its own msg handler (e.g vDPA) can benefit from it as well.

Thanks

>
>         if (iotlb->limit &&
> @@ -69,7 +71,7 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb,
>                 return -ENOMEM;
>
>         map->start = start;
> -       map->size = last - start + 1;
> +       map->size = size;
>         map->last = last;
>         map->addr = addr;
>         map->perm = perm;
> --
> 2.35.1
>