From bedd7e93d01961fcb16a97ae45d93acf357e11f6 Mon Sep 17 00:00:00 2001 From: Jason Wang Date: Thu, 2 Sep 2021 13:44:12 +0800 Subject: [PATCH] virtio-net: fix use after unmap/free for sg When mergeable buffer is enabled, we try to set the num_buffers after the virtqueue elem has been unmapped. This will lead several issues, E.g a use after free when the descriptor has an address which belongs to the non direct access region. In this case we use bounce buffer that is allocated during address_space_map() and freed during address_space_unmap(). Fixing this by storing the elems temporarily in an array and delay the unmap after we set the the num_buffers. This addresses CVE-2021-3748. Reported-by: Alexander Bulekov Fixes: fbe78f4f55c6 ("virtio-net support") Cc: qemu-stable@nongnu.org Signed-off-by: Jason Wang https://github.com/qemu/qemu/commit/bedd7e93d01961fcb16a97ae45d93acf357e11f6 CVE: CVE-2021-3748 Upstream-Status: Backport Signed-off-by: Chee Yang Lee --- hw/net/virtio-net.c | 39 ++++++++++++++++++++++++++++++++------- 1 file changed, 32 insertions(+), 7 deletions(-) diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c index 16d20cdee52a..f205331dcf8c 100644 --- a/hw/net/virtio-net.c +++ b/hw/net/virtio-net.c @@ -1746,10 +1746,13 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf, VirtIONet *n = qemu_get_nic_opaque(nc); VirtIONetQueue *q = virtio_net_get_subqueue(nc); VirtIODevice *vdev = VIRTIO_DEVICE(n); + VirtQueueElement *elems[VIRTQUEUE_MAX_SIZE]; + size_t lens[VIRTQUEUE_MAX_SIZE]; struct iovec mhdr_sg[VIRTQUEUE_MAX_SIZE]; struct virtio_net_hdr_mrg_rxbuf mhdr; unsigned mhdr_cnt = 0; - size_t offset, i, guest_offset; + size_t offset, i, guest_offset, j; + ssize_t err; if (!virtio_net_can_receive(nc)) { return -1; @@ -1780,6 +1783,12 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf, total = 0; + if (i == VIRTQUEUE_MAX_SIZE) { + virtio_error(vdev, "virtio-net unexpected long buffer chain"); + err = size; + goto err; + } + elem = virtqueue_pop(q->rx_vq, sizeof(VirtQueueElement)); if (!elem) { if (i) { @@ -1791,7 +1800,8 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf, n->guest_hdr_len, n->host_hdr_len, vdev->guest_features); } - return -1; + err = -1; + goto err; } if (elem->in_num < 1) { @@ -1799,7 +1809,8 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf, "virtio-net receive queue contains no in buffers"); virtqueue_detach_element(q->rx_vq, elem, 0); g_free(elem); - return -1; + err = -1; + goto err; } sg = elem->in_sg; @@ -1836,12 +1847,13 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf, if (!n->mergeable_rx_bufs && offset < size) { virtqueue_unpop(q->rx_vq, elem, total); g_free(elem); - return size; + err = size; + goto err; } - /* signal other side */ - virtqueue_fill(q->rx_vq, elem, total, i++); - g_free(elem); + elems[i] = elem; + lens[i] = total; + i++; } if (mhdr_cnt) { @@ -1851,10 +1863,23 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf, &mhdr.num_buffers, sizeof mhdr.num_buffers); } + for (j = 0; j < i; j++) { + /* signal other side */ + virtqueue_fill(q->rx_vq, elems[j], lens[j], j); + g_free(elems[j]); + } + virtqueue_flush(q->rx_vq, i); virtio_notify(vdev, q->rx_vq); return size; + +err: + for (j = 0; j < i; j++) { + g_free(elems[j]); + } + + return err; } static ssize_t virtio_net_do_receive(NetClientState *nc, const uint8_t *buf,