Re: [ovs-dev] [PATCH net-next] net: openvswitch: allow providing upcall pid for the 'execute' command

[Flavio Leitner <fbl@sysclose.org>]

On Thu, 3 Jul 2025 13:15:17 +0200
Ilya Maximets <i.maximets@ovn.org> wrote:

> On 7/3/25 1:04 PM, Flavio Leitner wrote:
> > On Thu, 3 Jul 2025 10:38:49 +0200
> > Ilya Maximets <i.maximets@ovn.org> wrote:
> >   
> >> On 7/3/25 1:08 AM, Flavio Leitner wrote:  
> >>>>>> @@ -651,6 +654,10 @@ static int ovs_packet_cmd_execute(struct sk_buff
> >>>>>> *skb, struct genl_info *info) !!(hash & OVS_PACKET_HASH_L4_BIT));
> >>>>>>  	}
> >>>>>>  
> >>>>>> +	if (a[OVS_PACKET_ATTR_UPCALL_PID])
> >>>>>> +		upcall_pid =
> >>>>>> nla_get_u32(a[OVS_PACKET_ATTR_UPCALL_PID]);
> >>>>>> +	OVS_CB(packet)->upcall_pid = upcall_pid;    
> >>>
> >>> Since this is coming from userspace, does it make sense to check if the
> >>> upcall_pid is one of the pids in the dp->upcall_portids array?    
> >>
> >> Not really.  IMO, this would be an unnecessary artificial restriction.
> >> We're not concerned about security here since OVS_PACKET_CMD_EXECUTE
> >> requires the same privileges as the OVS_DP_CMD_NEW or the
> >> OVS_DP_CMD_SET.  
> > 
> > What if the userspace is buggy or compromised?
> > It seems netlink API will return -ECONNREFUSED and the upcall is dropped.
> > Therefore, we would be okay either way, correct?  
> 
> If the userspace is compromised, it can overwrite the upcall_portids
> and do many other things, since the userspace application here has a
> CAP_NET_ADMIN.  And if it's buggy, then the packet will be just dropped
> on validation or on the upcall, there isn't much difference.
> 
> It's a responsibility of the userspace application to make sure these
> sockets exist before passing PIDs into the kernel.  From the kernel's
> perspective dropping the upcall is completely fine.  So, yes, we should
> be OK.

ack, thanks!
--
Flavio Leitner