From b0c057ca7e835b36c6050c7627634b664796c1d6 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Thu, 13 Feb 2014 11:45:11 +0200 Subject: [PATCH] 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 Acked-by: Jason Wang Signed-off-by: David S. Miller --- drivers/vhost/net.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 41be4de37e81..a0fa5de210cf 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -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); -- 2.20.1