On Tue, Mar 27, 2018 at 05:43:14PM +0800, Jason Wang wrote:

On 2018年03月27日 17:28, Darren Kenny wrote:

quoted

Hi Jason,

On Tue, Mar 27, 2018 at 11:47:22AM +0800, Jason Wang wrote:

quoted

We tried to remove vq poll from wait queue, but do not check whether
or not it was in a list before. This will lead double free. Fixing
this by checking poll->wqh to make sure it was in a list.

This text seems at odds with the code below, instead of checking
poll-whq, you are removing that check...

Maybe the text needs rewording?

Yes, I admit it's bad, thanks for pointing out.

How about:

"Fixing this by switching to use vhost_poll_stop() which zeros poll->wqh
after removing poll from waitqueue to make sure it won't be freed twice."

Thanks

Let's be a bit more specific about the problem maybe?

when vhost's attempt to start polling a descriptor fails, we remove the
poll->wqh entry from wait queue but do not clear it, so the following
cleanup (e.g. on release) will attempt to remove it again.

To fix, switch to vhost_poll_stop() which zeros poll->wqh
after removing poll from waitqueue to make sure it won't be freed twice."


the patch itself is fine though:


Acked-by: Michael S. Tsirkin <mst@redhat.com>

quoted

Thanks,

Darren.

quoted

Reported-by: syzbot+c0272972b01b872e604a@syzkaller.appspotmail.com
Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting
backend")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/vhost/vhost.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 1b3e8d2d..5d5a9d9 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -212,8 +212,7 @@ int vhost_poll_start(struct vhost_poll *poll,

struct file *file)
    if (mask)
        vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
    if (mask & EPOLLERR) {
-        if (poll->wqh)
-            remove_wait_queue(poll->wqh, &poll->wait);
+        vhost_poll_stop(poll);
        ret = -EINVAL;
    }

-- 
2.7.4

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