Re: [PATCH net] virtio/vsock: fix sock refcnt bug on owner set failure

[Stefano Garzarella]

On Wed, May 31, 2023 at 03:35:30AM +0000, Bobby Eshleman wrote:
> On Thu, Jun 01, 2023 at 09:58:47AM +0200, Stefano Garzarella wrote:
> > On Wed, May 31, 2023 at 07:47:32PM +0000, Bobby Eshleman wrote:
> > > Previous to setting the owner the socket is found via
> > > vsock_find_connected_socket(), which returns sk after a call to
> > > sock_hold().
> > >
> > > If setting the owner fails, then sock_put() needs to be called.
> > >
> > > Fixes: f9d2b1e146e0 ("virtio/vsock: fix leaks due to missing skb owner")
> > > Signed-off-by: Bobby Eshleman <bobby.eshleman@xxxxxxxxxxxxx>
> > > ---
> > > net/vmw_vsock/virtio_transport_common.c | 1 +
> > > 1 file changed, 1 insertion(+)
> > >
> > > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > > index b769fc258931..f01cd6adc5cb 100644
> > > --- a/net/vmw_vsock/virtio_transport_common.c
> > > +++ b/net/vmw_vsock/virtio_transport_common.c
> > > @@ -1343,6 +1343,7 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
> > >
> > > 	if (!skb_set_owner_sk_safe(skb, sk)) {
> > > 		WARN_ONCE(1, "receiving vsock socket has sk_refcnt == 0\n");
> > > +		sock_put(sk);
> >
> > Did you have any warning, issue here?
> >
> > IIUC skb_set_owner_sk_safe() can return false only if the ref counter
> > is 0, so calling a sock_put() on it should have no effect except to
> > produce a warning.
>
> Oh yeah, you're totally right. I did not recall how
> skb_set_owner_sk_safe() worked internally and thought I'd introduced an
> uneven hold/put count with that prior patch when reading through the
> code again. I haven't seen any live issue, just misread the code.
>
> Sorry about that, feel free to ignore this patch.

No problem ;-)

Maybe we should add a comment on it.

Thanks,
Stefano