Re: [v3] nbd: fix potential NULL pointer fault in nbd_genl_disconnect
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@huawei.com>
> ---
> 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.
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