vhost: fix a theoretical race in device cleanup (b0c057ca) · Commits · 戴 / test

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>

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);

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