Bug ? [was: Re: icmp checksum with build_data()s]

Re, 

The (geek) party is going on ... and the techno music made me think of a 
potential bug in all builders using the "solution" I proposed bellow. 

Example:
 ptag = libnet_build_foo(); // <-- dont use l->total_size
 libnet_build_bar(); // <-- use l->total_size
 libnet_write(); // <-- Ok
 libnet_build_foo(..., ptag); // <--  BUG CAUSED HERE
 ... 

If the second build_foo() has a different size, then there will be an error 
in checksum computation as total_size will have changed :-( 

This need to be checked ... but it's too late for me now. 


 Fred Raynal 

Frédéric Raynal writes: 

> Hi, 
> 
> I am currently at Berlin (others there ?) 
> 
> As far as I can tell, you sould not use it that way: the checksums are
> computed according to what is in the pblock, not after.  
> 
> But you are right here: this problem is also present for all other
> packets that do include paylaod in the checksum computation :( 
> 
> raynal@Joker:~/LIBNET/libnet/src$ grep "h =" *c|grep payload
> libnet_build_cdp.c:    h = LIBNET_CDP_H + len + payload_s;
> libnet_build_icmp.c:    h = LIBNET_ICMPV4_ECHO_H + payload_s; /* hl for checksum */
> libnet_build_icmp.c:    h = LIBNET_ICMPV4_MASK_H + payload_s; /* hl for checksum */
> libnet_build_icmp.c:    h = LIBNET_ICMPV4_TS_H + payload_s;        /* hl for checksum */
> libnet_build_icmp.c:    h = LIBNET_ICMPV4_UNREACH_H + payload_s + l->total_size; 
> libnet_build_icmp.c:    h = LIBNET_ICMPV4_TIMXCEED_H + payload_s + l->total_size; 
> libnet_build_icmp.c:    h = LIBNET_ICMPV4_REDIRECT_H + payload_s + l->total_size; 
> libnet_build_ospf.c:    h = LIBNET_OSPF_H + payload_s + len;
> libnet_build_ospf.c:    h = len + payload_s;
> libnet_build_vrrp.c:    h = LIBNET_VRRP_H + payload_s; 
> 
> 
> Without any garantee, the solution might be to systematically include
> "+ l->total_size;" so that the data is included each time it is
> required for the checksum. 
> 
> 
> 	Fred Raynal 
>