Skip Menu |
 

This queue is for tickets about the Net-RawIP CPAN distribution.

Report information
The Basics
Id: 67710
Status: new
Priority: 0/
Queue: Net-RawIP

People
Owner: Nobody in particular
Requestors:
Cc:
AdminCc:

Bug Information
Severity: (no value)
Broken in: (no value)
Fixed in: (no value)



From: gregoa [...] cpan.org
Subject: libnet-rawip-perl: miscalculates header checksums
Download (untitled) / with headers
text/plain 1.7k
[ This bug has been forwarded from http://bugs.debian.org/623634 ] From: "Steinar H. Gunderson" <sgunderson@bigfoot.com> To: Debian Bug Tracking System <submit@bugs.debian.org> Subject: Bug#623634: libnet-rawip-perl: miscalculates header checksums Date: Fri, 22 Apr 2011 01:28:29 +0200 Reply-To: "Steinar H. Gunderson" <sgunderson@bigfoot.com>, 623634@bugs.debian.org Hi, It seems Net::RawIP, if you run a script using it long enough (as in millions of generated UDP packets), eventually generates bogus UDP checksums in the packets it's sending out (tcpdump freaks out, the end hosts start ignoring them). I took a look at the source, and it seems the following fragment from RawIP.xs in the udp_pkt_creat() function is the culprit: memcpy(ptr,(u_char*)&piu,20); memcpy(ptr+20,SvPV(ip_opts,PL_na),SvCUR(ip_opts)); memcpy(ptr+20+SvCUR(ip_opts),(u_char*)&piu + 20,8); ((struct iphdr*)ptr)->check = in_cksum((unsigned short *)ptr,iplen); RETVAL = newSVpv((char*)ptr, sizeof(IUPKT)+SvCUR(ip_opts)); You can't use cast-as-lvalue like this; it is an aliasing violation, and with newer gcc seemingly something wrong happens here. The easiest way to fix this is usually by using memcpy (which has specific exceptions in POSIX from the aliasing rules), like this: unsigned short cksum; [...] cksum = in_cksum((unsigned short *)ptr,iplen); memcpy(&((struct iphdr*)ptr)->check, &cksum, sizeof(cksum)); Adding this fragment seems to have fixed the issue for us; at least it's running stable for a day or so. Granted, we also run with noopt nostrip, so it _could_ be something else, but it really sticks out as a sore thumb. FWIW, there are similar fragments many other places in the code, so you should probably fix all of them.


This service is sponsored and maintained by Best Practical Solutions and runs on Perl.org infrastructure.

Please report any issues with rt.cpan.org to rt-cpan-admin@bestpractical.com.