Re: [PATCH] net/vhost-net: do not assert on null pointer return from tap_get_vhost_net()

[Ani Sinha]

> On 28-Jun-2023, at 5:12 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> 
> On Wed, Jun 28, 2023 at 04:58:04PM +0530, Ani Sinha wrote:
>> When 'vhost=off' or no vhost specific options at all are passed for the tap
>> net-device backend, tap_get_vhost_net() can return NULL. The function
>> net_init_tap_one() does not call vhost_net_init() on such cases and therefore
>> vhost_net pointer within the tap device state structure remains NULL. Hence,
>> assertion here on a NULL pointer return from tap_get_vhost_net() would not be
>> correct. Remove it and fix the crash generated by qemu upon initialization in
>> the following call chain :
>> 
>> qdev_realize() -> pci_qdev_realize() -> virtio_device_realize() ->
>> virtio_bus_device_plugged() -> virtio_net_get_features() -> get_vhost_net()
>> 
>> fixes: 0e994668d00c9c ("vhost_net: add an assertion for TAP client backends")
>> Signed-off-by: Ani Sinha <anisinha@redhat.com>
> 
> I added a bunch of tags and sent it upstream. Take a look
> at the pull request so you can do it yourself going
> forward, pls.

I thought only maintainers sends PR? Do you have any handy scripts?

> 
>> ---
>> hw/net/vhost_net.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>> 
>> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
>> index 6db23ca323..6b958d6363 100644
>> --- a/hw/net/vhost_net.c
>> +++ b/hw/net/vhost_net.c
>> @@ -507,7 +507,12 @@ VHostNetState *get_vhost_net(NetClientState *nc)
>>     switch (nc->info->type) {
>>     case NET_CLIENT_DRIVER_TAP:
>>         vhost_net = tap_get_vhost_net(nc);
>> -        assert(vhost_net);
>> +        /*
>> +         * tap_get_vhost_net() can return NULL if a tap net-device backend 
>> is
>> +         * created with 'vhost=off' option, 'vhostforce=off' or no vhost or
>> +         * vhostforce or vhostfd options at all. Please see 
>> net_init_tap_one().
>> +         * Hence, we omit the assertion here.
>> +         */
>>         break;
>> #ifdef CONFIG_VHOST_NET_USER
>>     case NET_CLIENT_DRIVER_VHOST_USER:
>> -- 
>> 2.39.1
>