Re: [PATCH 5/5] net/tap: net_init_tap_one(): fix net-client leak on failure path

[Vladimir Sementsov-Ogievskiy]

12.01.2021 07:53, Jason Wang wrote:
> On 2020/12/22 上午3:06, Vladimir Sementsov-Ogievskiy wrote:
> > net_tap_fd_init() allocates new NetClientState through
> > qemu_new_net_client(). We should free it on failure path.
> >
> > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> > ---
> >
> > Attention: it's an intuitive patch.
> >
> > I see, that net-client is leaked. May be it's still freed some tricky
> > way? And I don't understand the whole logic of qemu_del_net_client(),
> > it's just the only public interface to free net-client I found.
>
>
> Your patch looks correct and it's indeed a leak.
>
> I wonder whether it's better to do the cleanup in the free_fail label in 
> net_init_tap(). The reason is that we need deal with case of multiqueue. Though 
> qemu_del_net_client() can handle this but it's not clear if we do it in 
> net_init_tap_one().

Sorry for so long delay :(

Now I'm thinking about reviving this series. But I don't understand what you 
mean about multiqueue.. I think, if some function allocates a resource, we 
should release the resource on failure path in this function, not in the 
caller. Good functions tries to roll-back any visible changes on failure.. What 
am I missing?

> >   net/tap.c | 9 ++++++++-
> >   1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/tap.c b/net/tap.c
> > index 89ea04862b..ba4c34af3d 100644
> > --- a/net/tap.c
> > +++ b/net/tap.c
> > @@ -711,7 +711,7 @@ static void net_init_tap_one(const NetdevTapOptions *tap, 
> > NetClientState *peer,
> >       ret = tap_set_sndbuf(s->fd, tap, errp);
> >       if (ret < 0) {
> > -        return;
> > +        goto fail;
> >       }
> >       if (tap->has_fd || tap->has_fds) {
> > @@ -739,13 +739,20 @@ static void net_init_tap_one(const NetdevTapOptions *tap, 
> > NetClientState *peer,
> >           if (ret < 0) {
> >               if (tap->has_vhostforce && tap->vhostforce) {
> >                   error_propagate(errp, err);
> > +                goto fail;
> >               } else {
> >                   warn_report_err(err);
> >               }
> >           }
> >       } else if (vhostfdname) {
> >           error_setg(errp, "vhostfd(s)= is not valid without vhost");
> > +        goto fail;
> >       }
> > +
> > +    return;
> > +
> > +fail:
> > +    qemu_del_net_client(&s->nc);
> >   }
> >   static int get_fds(char *str, char *fds[], int max)


--
Best regards,
Vladimir