Re: [RFC Patch] net: reserve ports for applications using fixed portnumbers

[Cong Wang]

Eric Dumazet wrote:
> Le mardi 02 fÃvrier 2010 Ã 23:30 -0500, Amerigo Wang a Ãcrit :
> > This patch introduces /proc/sys/net/ipv4/ip_local_reserved_ports,
> > it can be used like ip_local_port_range, but this is used to
> > reserve ports for third-party applications which use fixed
> > port numbers within ip_local_port_range.
> >
> > This only affects the applications which call socket functions
> > like bind(2) with port number 0, to prevent the kernel getting the ports
> > within the specified range for them. For applications which use fixed
> > port number, it will have no effects.
> >
> > Any comments are welcome.
> >
> > Signed-off-by: WANG Cong <amwang@xxxxxxxxxx>
> > Cc: David Miller <davem@xxxxxxxxxxxxx>
> > Cc: Neil Horman <nhorman@xxxxxxxxxxxxx>
> > Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
>
> >  		.procname	= "igmp_max_memberships",
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index f0126fd..83045ca 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -210,8 +210,11 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
> >  		inet_get_local_port_range(&low, &high);
> >  		remaining = (high - low) + 1;
> >  
> > +again:
> >  		rand = net_random();
> >  		first = (((u64)rand * remaining) >> 32) + low;
> > +		if (inet_is_reserved_local_port(first))
> > +			goto again;
> >  		/*
> >  		 * force rand to be an odd multiple of UDP_HTABLE_SIZE
> >  		 */
>
> Unless I misread the patch, you are checking only the 'first' port that
> udp_lib_get_port() chose.
>
> I would use inet_get_local_reserved_ports(&min_res, &max_res);
> and check every port that we chose in the loop to avoid it if necessary.

Hmm, right, 'first' is used to do iteration, but I did missed 'last'.
Thanks! I will fix this in the next update.

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