vhost: fix a theoretical race in device cleanup
vhost_zerocopy_callback accesses VQ right after it drops a ubuf
reference. In theory, this could race with device removal which waits
on the ubuf kref, and crash on use after free.
Do all accesses within rcu read side critical section, and synchronize
on release.
Since callbacks are always invoked from bh, synchronize_rcu_bh seems
enough and will help release complete a bit faster.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 41be4de..a0fa5de 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -308,6 +308,8 @@
struct vhost_virtqueue *vq = ubufs->vq;
int cnt;
+ rcu_read_lock_bh();
+
/* set len to mark this desc buffers done DMA */
vq->heads[ubuf->desc].len = success ?
VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN;
@@ -322,6 +324,8 @@
*/
if (cnt <= 1 || !(cnt % 16))
vhost_poll_queue(&vq->poll);
+
+ rcu_read_unlock_bh();
}
/* Expects to be always run from workqueue - which acts as
@@ -799,6 +803,8 @@
fput(tx_sock->file);
if (rx_sock)
fput(rx_sock->file);
+ /* Make sure no callbacks are outstanding */
+ synchronize_rcu_bh();
/* We do an extra flush before freeing memory,
* since jobs can re-queue themselves. */
vhost_net_flush(n);