Re: [net-next PATCH v4 3/3] net: reserve ports for applications usingfixed port numbers
From: Cong Wang
Date: Wed Feb 17 2010 - 11:10:11 EST
Eric Dumazet wrote:
Le mardi 16 fÃvrier 2010 Ã 21:06 +0800, Cong Wang a Ãcrit :
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
I don't think so, if you want to avoid race condition, you just need to
write the reserved ports before any networking application starts, IOW,
as early as possible during boot.
Thanks.
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