Raw socket sendto() failure in OS X

Question

When I open a raw socket is OS X, construct my own udp packet (headers and data), and call sendto(), I get the error "Invalid Argument". Here is a sample program "rawudp.c" from the web site http://www.tenouk.com/Module43a.html that demonstrates this problem. The program (after adding string and stdlib #includes) runs under Fedora 10 but fails with "Invalid Argument" under OS X. Can anyone suggest why this fails in OS X? I have looked and looked and looked at the sendto() call, but all the parameters look good. I'm running the code as root, etc. Is there perhaps a kernel setting that prevents even uid 0 executables from sending packets through raw sockets in OS X Snow Leopard? Thanks.

Answer 1

I may have solved the mystery. I too crafted a raw socket example, which runs fine on Linux, but got "Invalid Argument" error on OS X 10.6.
I encountered this page "FreeBSD socket bugs and peculiarities" while googling for an answer. And it says:

Writing to RAW sockets

---

- ip_len and ip_off must be in host byte order

So I replace

ip.ip_len = htons(len);

with

ip.ip_len = len;

on OS X. And it works, however strange it is.

Answer 2

user37278, I ran the same program on my Mac OS X (Snow Leopard) and get the same error message. I found the problem is that the custom IP header structure is incoherent with the IP header format. (Might have something to do difference in machines.. I'm not sure).

What I did was I removed his custom IP header structure and used the IP header struct included with Mac OS X. The header information is defined in <netinet/ip.h> and the struct is struct ip. I also found another struct called struct iphdr and I'm not sure the difference.

The headers I included are <netinet/ip.h> <netinet/udp.h> <netinet/in.h> <arpa/inet.h>

Hope this helps.