Re: Add IP address ioctl (SIOCAIFADDR) from jail is called with host credentials

On Fri, 23 Jun 2023, at 7:53 AM, Shivank Garg wrote:
> Hi,
> 
> I want to check credentials of the thread setting the IP address with SIOCAIFADDR ioctl.
> If the thread is jailed (jailed(td_ucred) == 1), I'm applying some checks on ip address.
> 
> My expectation was that (cred->cr_prison != &prison0) for an ifconfig call made by the jail.
If you’re using -head, it’s a bit more complicated. ifconfig(8) uses rtnetlink(4) interfaces to communicate with the kernel. Privilege check is done in Netlink:  https://github.com/freebsd/freebsd-src/blob/764464af49688e74fd6d803df0404ca4726dd460/sys/netlink/route/iface.c#L1472 . After that, (as of now) netlink calls ioctl code from its own kernel thread, which may be the reason of the behavior you’re observing.
> However, it is showing me some weird behavior. Here are the logs for a tweaked kernel:
> 
> @@ -339,7 +343,7 @@ in_control(struct socket *so, u_long cmd, void *data, struct ifnet *ifp,
>                 return (EADDRNOTAVAIL);
>         struct ucred *cred = (td != NULL) ? td->td_ucred : NULL;
> -
> +       printf("in_control jailed? %d jid %d prison_owns_vnet? %d\n",jailed(cred),cred->cr_prison->pr_id,prison_owns_vnet(cred));
> 
> # jexec 1 ifconfig epair0b inet 169.254.123.101/24 up
> 
> Dmesg logs:
> *[256] in_control jailed? 0 jid 0 prison_owns_vnet? 1*
> 
> Cred value indicates host and jail is 0 but the PR_VNET flag is set.
> 
> Is this behavior expected? or something going wrong - what's the next debug step?
> 
> I greatly appreciate your help!
> 
> Thanks,
> Shivank

/Alexander