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Re: [Qemu-devel] [PATCH v2] virtio-net: Always check for guest header le
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v2] virtio-net: Always check for guest header length |
Date: |
Mon, 22 Jul 2019 04:59:48 -0400 |
On Fri, Jul 19, 2019 at 03:21:15PM +0000, Oleinik, Alexander wrote:
> While fuzzing the virtio-net tx vq, I ran into an assertion failure due
> to iov_copy offsets larger than the total iov size. Though there is
> a check to cover this, it does not execute when !n->has_vnet_hdr. This
> change always copies the guest header into the mhdr buffer and checks its
> length, even if mhdr is not needed.
>
> The call stack for the assertion failure:
>
> #8 in __assert_fail (libc.so.6+0x300f1)
> #9 in iov_copy iov.c:266:5
> #10 in virtio_net_flush_tx virtio-net.c:2073:23
> #11 in virtio_net_tx_bh virtio-net.c:2197:11
> #12 in aio_bh_poll async.c:118:13
> #13 in aio_dispatch aio-posix.c:460:5
> #14 in aio_ctx_dispatch async.c:261:5
> #15 in g_main_context_dispatch (libglib-2.0.so.0+0x4df2d)
> #16 in glib_pollfds_poll main-loop.c:213:9
> #17 in os_host_main_loop_wait main-loop.c:236
> #18 in main_loop_wait main-loop.c:512
> #19 in virtio_net_tx_fuzz virtio-net-fuzz.c:160:3
>
> Signed-off-by: Alexander Oleinik <address@hidden>
Acked-by: Michael S. Tsirkin <address@hidden>
> ---
> hw/net/virtio-net.c | 19 ++++++++++++-------
> 1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index b9e1cd71cf..003436b53c 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -2035,14 +2035,19 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
> return -EINVAL;
> }
>
> - if (n->has_vnet_hdr) {
> - if (iov_to_buf(out_sg, out_num, 0, &mhdr, n->guest_hdr_len) <
> + /*
> + * Even if !n->has_vnet_hdr and we dont need mhdr, we still need this
> + * to check that out_sg contains at least guest_hdr_len bytes
> + */
> + if (iov_to_buf(out_sg, out_num, 0, &mhdr, n->guest_hdr_len) <
> n->guest_hdr_len) {
> - virtio_error(vdev, "virtio-net header incorrect");
> - virtqueue_detach_element(q->tx_vq, elem, 0);
> - g_free(elem);
> - return -EINVAL;
> - }
> + virtio_error(vdev, "virtio-net header incorrect");
> + virtqueue_detach_element(q->tx_vq, elem, 0);
> + g_free(elem);
> + return -EINVAL;
> + }
> +
> + if (n->has_vnet_hdr) {
> if (n->needs_vnet_hdr_swap) {
> virtio_net_hdr_swap(vdev, (void *) &mhdr);
> sg2[0].iov_base = &mhdr;
> --
> 2.20.1