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Commit b0c057ca authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by David S. Miller
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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: default avatarMichael S. Tsirkin <mst@redhat.com>
Acked-by: default avatarJason Wang <jasowang@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0ad8b480

drivers/vhost/net.c

+6 −0
Original line number Diff line number Diff line
@@ -308,6 +308,8 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) 
	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 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) 
	 */

	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 @@ static int vhost_net_release(struct inode *inode, struct file *f) 
		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);