Re: [patch] ipvs: prevent some underflows

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	Hello,

On Fri, 5 Jun 2015, Dan Carpenter wrote:

> @@ -1363,7 +1363,8 @@ static int set_sync_mesg_maxlen(struct net *net, int sync_state)

	May be we should use min(dev->mtu, 1500) instead of
dev->mtu to avoid sending too large packets for the common
case.

>  		       sizeof(struct udphdr) -
>  		       SYNC_MESG_HEADER_LEN - 20) / SIMPLE_CONN_SIZE;
>  		ipvs->send_mesg_maxlen = SYNC_MESG_HEADER_LEN +
> -			SIMPLE_CONN_SIZE * min(num, MAX_CONNS_PER_SYNCBUFF);
> +			SIMPLE_CONN_SIZE * min_t(uint, num,
> +						 MAX_CONNS_PER_SYNCBUFF);

	ipvs->send_mesg_maxlen = max(min(dev->mtu, 1500) -
		sizeof(struct iphdr) - sizeof(struct udphdr),
		/* Some new const is needed here: */
		2 * FULL_CONN_SIZE);

	And may be we should add more correct checks in
ip_vs_sync_conn() in case dev->mtu was changed after thread
start. Currently, it is assumed that fresh new buffer from
ip_vs_sync_buff_create() will have space for at least one
message... We can even set inet->pmtudisc to IP_PMTUDISC_DONT
so that packets can be fragmented for too small MTU.

>  		IP_VS_DBG(7, "setting the maximum length of sync sending "
>  			  "message %d.\n", ipvs->send_mesg_maxlen);
>  	} else if (sync_state == IP_VS_STATE_BACKUP) {
> @@ -1371,8 +1372,11 @@ static int set_sync_mesg_maxlen(struct net *net, int sync_state)
>  		if (!dev)
>  			return -ENODEV;
>  
> -		ipvs->recv_mesg_maxlen = dev->mtu -
> -			sizeof(struct iphdr) - sizeof(struct udphdr);
> +		if (dev->mtu < sizeof(struct iphdr) + sizeof(struct udphdr))
> +			ipvs->recv_mesg_maxlen = 0;
> +		else
> +			ipvs->recv_mesg_maxlen = dev->mtu -
> +				sizeof(struct iphdr) - sizeof(struct udphdr);

	May be ipvs->recv_mesg_maxlen = max(dev->mtu, 1500);
This is single buffer allocated when backup starts...

>  		IP_VS_DBG(7, "setting the maximum length of sync receiving "
>  			  "message %d.\n", ipvs->recv_mesg_maxlen);
>  	}
> 

Regards

--
Julian Anastasov <ja@xxxxxx>
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