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SubjectRe: [net-next PATCH v4 3/3] net: reserve ports for applications using fixed port numbers
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Le mardi 16 février 2010 à 21:06 +0800, Cong Wang a écrit :
> Octavian Purdila wrote:
> > On Tuesday 16 February 2010 11:37:04 you wrote:
> >>> BUILD_BUG_ON(sizeof(struct inet_skb_parm) > sizeof(dummy_skb->cb));
> >>>
> >>> + sysctl_local_reserved_ports = kzalloc(65536 / 8, GFP_KERNEL);
> >>> + if (!sysctl_local_reserved_ports)
> >>> + goto out;
> >>> +
> >> I think we should also consider the ports in ip_local_port_range,
> >> since we can only reserve the ports in that range.
> >>
> >
> > That is subject to changes at runtime, which means we will have to readjust
> > the bitmap at runtime which introduces the need for additional synchronization
> > operations which I would rather avoid.
>
> Why? As long as the bitmap is global, this will not be hard.
>
> Consider that if one user writes a port number which is beyond
> the ip_local_port_range into ip_local_reserved_ports, we should
> not accept this, because it doesn't make any sense. But with your
> patch, we do.

I disagree with you. This is perfectly OK.

A port not being flagged in ip_local_reserved_ports doesnt mean it can
be used for allocation.

If you want to really block ports from being used at boot, you could for
example :

# temporarly reduce the ip_local_port_range
echo "61000 61001" >/proc/sys/net/ipv4/ip_local_port_range
# Build our bitmap (could be slow, if a remote database is read)
for port in $LIST_RESERVED_PORT
do
echo $port >/proc/sys/net/ipv4/ip_local_reserved_ports
done
echo "10000 61000" >/proc/sys/net/ipv4/ip_local_port_range


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