Re: [v3] nbd: fix potential NULL pointer fault in nbd_genl_disconnect

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在 2020/2/11 1:05, Mike Christie 写道:
On 02/10/2020 01:32 AM, Sun Ke wrote:
Open /dev/nbdX first, the config_refs will be 1 and
the pointers in nbd_device are still null. Disconnect
/dev/nbdX, then reference a null recv_workq. The
protection by config_refs in nbd_genl_disconnect is useless.

To fix it, just add a check for a non null task_recv in
nbd_genl_disconnect.

Signed-off-by: Sun Ke <sunke32@xxxxxxxxxx>
---
v1 -> v2:
Add an omitted mutex_unlock.

v2 -> v3:
Add nbd->config_lock, suggested by Josef.
---
  drivers/block/nbd.c | 8 ++++++++
  1 file changed, 8 insertions(+)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index b4607dd96185..870b3fd0c101 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -2008,12 +2008,20 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
  		       index);
  		return -EINVAL;
  	}
+	mutex_lock(&nbd->config_lock);
  	if (!refcount_inc_not_zero(&nbd->refs)) {
+		mutex_unlock(&nbd->config_lock);
  		mutex_unlock(&nbd_index_mutex);
  		printk(KERN_ERR "nbd: device at index %d is going down\n",
  		       index);
  		return -EINVAL;
  	}
+	if (!nbd->recv_workq) {
+		mutex_unlock(&nbd->config_lock);
+		mutex_unlock(&nbd_index_mutex);
+		return -EINVAL;
+	}
+	mutex_unlock(&nbd->config_lock);
  	mutex_unlock(&nbd_index_mutex);
  	if (!refcount_inc_not_zero(&nbd->config_refs)) {
  		nbd_put(nbd);


With my other patch then we will not need this right? It handles your
case by just being integrated with the existing checks in:

nbd_disconnect_and_put->nbd_clear_sock->sock_shutdown

...

static void sock_shutdown(struct nbd_device *nbd)
{

....

         if (config->num_connections == 0)
                 return;


num_connections is zero for your case since we never did a
nbd_genl_disconnect so we would return here.


.

Hi Mike

Your point is not right totally.

Yes, config->num_connections is 0 and will return in sock_shutdown. Then it will back to nbd_disconnect_and_put and do flush_workqueue (nbd->recv_workq).

nbd_disconnect_and_put
	->nbd_clear_sock
		->sock_shutdown
	->flush_workqueue

Thanks,
Sun Ke




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