From: Juergen Gross jgross@suse.com
Commit 66e3531b33ee51dad17c463b4d9c9f52e341503d upstream.
When calling gnttab_end_foreign_access_ref() the returned value must be tested and the reaction to that value should be appropriate.
In case of failure in xennet_get_responses() the reaction should not be to crash the system, but to disable the network device.
The calls in setup_netfront() can be replaced by calls of gnttab_end_foreign_access(). While at it avoid double free of ring pages and grant references via xennet_disconnect_backend() in this case.
This is CVE-2022-23042 / part of XSA-396.
Reported-by: Demi Marie Obenour demi@invisiblethingslab.com Signed-off-by: Juergen Gross jgross@suse.com Reviewed-by: Jan Beulich jbeulich@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/xen-netfront.c | 48 +++++++++++++++++++++++++++++---------------- 1 file changed, 31 insertions(+), 17 deletions(-)
--- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c @@ -988,7 +988,6 @@ static int xennet_get_responses(struct n struct device *dev = &queue->info->netdev->dev; struct bpf_prog *xdp_prog; struct xdp_buff xdp; - unsigned long ret; int slots = 1; int err = 0; u32 verdict; @@ -1030,8 +1029,13 @@ static int xennet_get_responses(struct n goto next; }
- ret = gnttab_end_foreign_access_ref(ref, 0); - BUG_ON(!ret); + if (!gnttab_end_foreign_access_ref(ref, 0)) { + dev_alert(dev, + "Grant still in use by backend domain\n"); + queue->info->broken = true; + dev_alert(dev, "Disabled for further use\n"); + return -EINVAL; + }
gnttab_release_grant_reference(&queue->gref_rx_head, ref);
@@ -1252,6 +1256,10 @@ static int xennet_poll(struct napi_struc &need_xdp_flush);
if (unlikely(err)) { + if (queue->info->broken) { + spin_unlock(&queue->rx_lock); + return 0; + } err: while ((skb = __skb_dequeue(&tmpq))) __skb_queue_tail(&errq, skb); @@ -1916,7 +1924,7 @@ static int setup_netfront(struct xenbus_ struct netfront_queue *queue, unsigned int feature_split_evtchn) { struct xen_netif_tx_sring *txs; - struct xen_netif_rx_sring *rxs; + struct xen_netif_rx_sring *rxs = NULL; grant_ref_t gref; int err;
@@ -1936,21 +1944,21 @@ static int setup_netfront(struct xenbus_
err = xenbus_grant_ring(dev, txs, 1, &gref); if (err < 0) - goto grant_tx_ring_fail; + goto fail; queue->tx_ring_ref = gref;
rxs = (struct xen_netif_rx_sring *)get_zeroed_page(GFP_NOIO | __GFP_HIGH); if (!rxs) { err = -ENOMEM; xenbus_dev_fatal(dev, err, "allocating rx ring page"); - goto alloc_rx_ring_fail; + goto fail; } SHARED_RING_INIT(rxs); FRONT_RING_INIT(&queue->rx, rxs, XEN_PAGE_SIZE);
err = xenbus_grant_ring(dev, rxs, 1, &gref); if (err < 0) - goto grant_rx_ring_fail; + goto fail; queue->rx_ring_ref = gref;
if (feature_split_evtchn) @@ -1963,22 +1971,28 @@ static int setup_netfront(struct xenbus_ err = setup_netfront_single(queue);
if (err) - goto alloc_evtchn_fail; + goto fail;
return 0;
/* If we fail to setup netfront, it is safe to just revoke access to * granted pages because backend is not accessing it at this point. */ -alloc_evtchn_fail: - gnttab_end_foreign_access_ref(queue->rx_ring_ref, 0); -grant_rx_ring_fail: - free_page((unsigned long)rxs); -alloc_rx_ring_fail: - gnttab_end_foreign_access_ref(queue->tx_ring_ref, 0); -grant_tx_ring_fail: - free_page((unsigned long)txs); -fail: + fail: + if (queue->rx_ring_ref != GRANT_INVALID_REF) { + gnttab_end_foreign_access(queue->rx_ring_ref, 0, + (unsigned long)rxs); + queue->rx_ring_ref = GRANT_INVALID_REF; + } else { + free_page((unsigned long)rxs); + } + if (queue->tx_ring_ref != GRANT_INVALID_REF) { + gnttab_end_foreign_access(queue->tx_ring_ref, 0, + (unsigned long)txs); + queue->tx_ring_ref = GRANT_INVALID_REF; + } else { + free_page((unsigned long)txs); + } return err; }