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Thread: NAT broken in (at least) 1.9.2.7 & 1.9.5.0 - FIXED!

  1. #1
    Join Date
    Sep 2005
    Location
    Berlin, Germany
    Posts
    6

    NAT broken in (at least) 1.9.2.7 & 1.9.5.0 - FIXED!

    Playing around with my WL500g.Deluxe i found out, that the NAT support is somehow broken.

    NAT only works for /24 networks, regardless which netmask is configured for the LAN interface. The reason is a bug in src/router/rc/firewall_ex.c in the function ip2class. This function is invoked to calculate the numeric network class for the iptables configuration stored in /tmp/nat_rules.

    This is the original ASUS code:

    Code:
    ip2class(char *lan_ip, char *netmask, char *buf)
    {
            unsigned int val, ip;
            struct in_addr in;
            int i=0;
    
            // only handle class A,B,C      
            val = (unsigned int)inet_addr(netmask);
            ip = (unsigned int)inet_addr(lan_ip);
            in.s_addr = ip & val;
            if (val==0xff00000) sprintf(buf, "%s/8", inet_ntoa(in));
            else if (val==0xffff0000) sprintf(buf, "%s/16", inet_ntoa(in));
            else sprintf(buf, "%s/24", inet_ntoa(in));
            dprintf(buf);   
    }
    It seems that this function supports only Class A,B and C (/8, /16 and /24) networks. But wait! The function inet_addr (from arpa/inet.h) returns the ip address in network byte order, so e.g. 255.255.255.0 will become 0x00ffffff (and not 0xffffff00). This means that the function ip2class above actually always returns "/24" because the else statement always matches.

    I found this bug in the 1.9.2.7 source (I'm using oleg's 1.9.2.7-6b), but I just checked 1.9.5.0 from ASUS - the bug is still there. ASUS told me, to post into this forum rather than directly contacting the developers.

    However, here is a fix. It also works with all possible netmasks:

    Code:
    ip2class(char *lan_ip, char *netmask, char *buf)
    {
            unsigned int val, ip;
            struct in_addr in;
            int i=0;
    
            // should handle all classes now        
            val = (unsigned int)inet_addr(netmask);
            ip = (unsigned int)inet_addr(lan_ip);
            in.s_addr = ip & val;
            val = ((val & 0xff000000) >> 24) + ((val & 0x00ff0000) >> 8) + ((val & 0x0000ff00) << 8) + (val & 0x000000ff) << 24);
            while (val!=0)
            {
                    val = val << 1;
                    i++;
            }
            sprintf(buf, "%s/%d", inet_ntoa(in), i);
            dprintf(buf);   
    }
    oleg: can you patch this into your next release, please?

  2. #2
    Join Date
    Dec 2003
    Location
    Russian Federation
    Posts
    8,353
    hm... yes, sure.

  3. #3
    Join Date
    Dec 2003
    Location
    Russian Federation
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    Applied like this:
    Code:
    	val = (unsigned int)inet_addr(netmask);
    
    	ip = (unsigned int)inet_addr(lan_ip);
    
    	in.s_addr = ip & val;
    
    
            for (val = ntohl(val); val; i++) 
            	val <<= 1;
           
            sprintf(buf, "%s/%d", inet_ntoa(in), i);

  4. #4
    Join Date
    Sep 2005
    Location
    Berlin, Germany
    Posts
    6
    Yes... ntohl() is the function I was looking for (and the function the ASUS developers forgot) ;-)

  5. #5
    Join Date
    Oct 2005
    Location
    Denmark
    Posts
    21
    Hi - where to get this fix?

  6. #6
    Join Date
    Dec 2003
    Location
    Russian Federation
    Posts
    8,353
    1.9.2.7-6c-pre5

  7. #7
    Join Date
    Oct 2005
    Location
    Denmark
    Posts
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    Post

    Quote Originally Posted by Oleg
    1.9.2.7-6c-pre5
    Thanks...

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