Subject: Re: v3 for tcp friends?

From: Li Yu <[email-masked]>
Date: Wed, 23 Jan 2013 15:21:25 +0800

于 2013年01月23日 14:46, Eric Dumazet 写道:
> On Wed, 2013-01-23 at 14:12 +0800, Li Yu wrote:
>> Oops, this hang is not since TCP friends patch!
>>
>> sk_sndbuf_get() is broken by 32 bits integer overflow
>> because of so large value in net.ipv4.tcp_{rmem,wmem}.
>>
>> but this hang also can be found in net-next.git
>> (3.8.0-rc3+), if we run below commands, then all new
>> TCP connections stop working!
>>
>> # when TCP friends is disabled
>> sysctl -w net.ipv4.tcp_rmem="4096 4294967296 4294967296" # 4GB
>> sysctl -w net.ipv4.tcp_wmem="4096 4294967296 4294967296"
>
> Right we need to make sure we dont overflow.
>
> Try the following fix :
>
> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> index a25e1d2..1459145 100644
> --- a/net/ipv4/sysctl_net_ipv4.c
> +++ b/net/ipv4/sysctl_net_ipv4.c
> @@ -549,14 +549,16 @@ static struct ctl_table ipv4_table[] = {
>   		.data		= &sysctl_tcp_wmem,
>   		.maxlen		= sizeof(sysctl_tcp_wmem),
>   		.mode		= 0644,
> -		.proc_handler	= proc_dointvec
> +		.extra1		= &zero,
> +		.proc_handler	= proc_dointvec_minmax
>   	},
>   	{
>   		.procname	= "tcp_rmem",
>   		.data		= &sysctl_tcp_rmem,
>   		.maxlen		= sizeof(sysctl_tcp_rmem),
>   		.mode		= 0644,
> -		.proc_handler	= proc_dointvec
> +		.extra1		= &zero,
> +		.proc_handler	= proc_dointvec_minmax
>   	},
>   	{
>   		.procname	= "tcp_app_win",
>
>
>
Thanks for so quick reply, I will test it soon.

however I suspect whether this patch could fix overflow if we merged TCP 
friends patch in future.

With TCP friends, we have source like below, or TCP friends should care 
this ?

static inline int sk_sndbuf_get(const struct sock *sk)
{
         if (sk->sk_friend)
                 return sk->sk_sndbuf + sk->sk_friend->sk_rcvbuf;
         else
                 return sk->sk_sndbuf;
}

static inline bool sk_stream_memory_free(const struct sock *sk)
{
         return sk_wmem_queued_get(sk) < sk_sndbuf_get(sk);
}

So sk_sndbuf_get() still may be overflow when we have right value in 
net.ipv4.tcp_{rmem,wmem}.

Thanks