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

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mardi 02 février 2010 à 23:30 -0500, Amerigo Wang a écrit :
> 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@redhat.com>
> Cc: David Miller <davem@davemloft.net>
> Cc: Neil Horman <nhorman@tuxdriver.com>
> Cc: Eric Dumazet <eric.dumazet@gmail.com>

>  		.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.