[libvirt] [PATCH v2 5/5] network: check accept_ra before enabling ipv6 forwarding

[Cedric Bosdonnat]

On Wed, 2017-03-22 at 07:16 -0400, John Ferlan wrote:
> [...]
> 
> > +
> > +static int
> > +virNetDevIPCheckIPv6ForwardingCallback(const struct nlmsghdr *resp,
> > +                                       void *opaque)
> > +{
> > +    struct rtmsg *rtmsg = NLMSG_DATA(resp);
> > +    int accept_ra = -1;
> > +    struct rtattr *rta;
> > +    char *ifname = NULL;
> > +    struct virNetDevIPCheckIPv6ForwardingData *data = opaque;
> > +    int ret = 0;
> > +    int len = RTM_PAYLOAD(resp);
> > +    int oif = -1;
> > +
> > +    /* Ignore messages other than route ones */
> > +    if (resp->nlmsg_type != RTM_NEWROUTE)
> > +        return ret;
> > +
> > +    /* Extract a few attributes */
> > +    for (rta = RTM_RTA(rtmsg); RTA_OK(rta, len); rta = RTA_NEXT(rta, len)) {
> > +        switch (rta->rta_type) {
> > +        case RTA_OIF:
> > +            oif = *(int *)RTA_DATA(rta);
> > +
> > +            if (!(ifname = virNetDevGetName(oif)))
> > +                goto error;
> > +            break;
> 
> Did you really mean to break from the for loop if ifname is set?  This
> breaks only from the switch/case.  Of course Coverity doesn't know much
> more than you'd be going back to the top of the for loop and could
> overwrite ifname again. It proclaims a resource leak...

In my dev version I was also getting the RTA_DST attribute to print some
debugging message that I removed in the submitted version. The break was
here between the switch cases.

In the current case I don't really care if we break out of the loop or not.
As there aren't that many attributes in an rtnetlink message to loop over,
breaking wouldn't gain a lot of cycles.

What I don't get though is what this break is actually doing? isn't it
for the switch case even though there is no other case after it?

--
Cedric

> John
> > +        }
> > +    }
> > +
> > +    /* No need to do anything else for non RA routes */
> > +    if (rtmsg->rtm_protocol != RTPROT_RA)
> > +        goto cleanup;
> > +
> > +    data->hasRARoutes = true;
> > +
> > +    /* Check the accept_ra value for the interface */
> > +    accept_ra = virNetDevIPGetAcceptRA(ifname);
> > +    VIR_DEBUG("Checking route for device %s, accept_ra: %d", ifname, accept_ra);
> > +
> > +    if (accept_ra != 2 && VIR_APPEND_ELEMENT(data->devices, data->ndevices, ifname) < 0)
> > +        goto error;
> > +
> > + cleanup:
> > +    VIR_FREE(ifname);
> > +    return ret;
> > +
> > + error:
> > +    ret = -1;
> > +    goto cleanup;
> > +}
> 
>