tcpdump mailing list archives
Re: pcap_inject() on loopback (FreeBSD)
From: Guy Harris <guy () alum mit edu>
Date: Sun, 15 Jun 2014 11:07:36 -0700
On Jun 15, 2014, at 5:23 AM, Fernando Gont <fernando () gont com ar> wrote:
I'm trying to send an IPv6 packet with pcap_inject() on the loopback interface of a FreeBSD 9.2 system. What I write with pcap_inect() is the IPv6 packet, preceded with the 4-byte AF header (which I set to PF_INET6 (which is 28) in host byte order). However, pcap_inject() fails with "send: Address family not supported by protocol family" and I also get this message on the console:: "looutput: af=31 unexpected" which would seem to indicate that pcap_inject() is overwriting the value I set with something else (pseudo_AF_HDRCMPLT?).
It indicates that *some* piece of code is overwriting that value. However, pcap_inject(), on systems with BPF, is: static int pcap_inject_bpf(pcap_t *p, const void *buf, size_t size) { int ret; ret = write(p->fd, buf, size); #ifdef __APPLE__ a bunch of code only used on OS X/iOS #endif /* __APPLE__ */ if (ret == -1) { snprintf(p->errbuf, PCAP_ERRBUF_SIZE, "send: %s", pcap_strerror(errno)); return (PCAP_ERROR); } return (ret); } so it's not what's setting pseudo_AF_HDRCMPLT. The offending code is in bpfwrite(): if (d->bd_hdrcmplt) dst.sa_family = pseudo_AF_HDRCMPLT; "dst" is handed to looutput() in sys/net/if_loop.c, which does /* BPF writes need to be handled specially. */ if (dst->sa_family == AF_UNSPEC) bcopy(dst->sa_data, &af, sizeof(af)); else af = dst->sa_family; The common code for Ethernet sends (ether_output()) explicitly handles both AF_UNSPEC *and* pseudo_AF_HDRCMPLT; the loopback driver needs to handle it as well, e.g. either /* BPF writes need to be handled specially. */ if (dst->sa_family == pseudo_AF_HDRCMPLT) bcopy(dst->sa_data, &af, sizeof(af)); else af = dst->sa_family; or /* BPF writes need to be handled specially. */ if (dst->sa_family == pseudo_AF_HDRCMPLT || dst->sa_family == AF_UNSPEC) bcopy(dst->sa_data, &af, sizeof(af)); else af = dst->sa_family; As the person who came across this bug, you should file a bug on this; if you can, CC me on it, or, if not, let me know what bug ID it gets assigned so that I can try to CC myself on it. _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- pcap_inject() on loopback (FreeBSD) Fernando Gont (Jun 15)
- Re: pcap_inject() on loopback (FreeBSD) Guy Harris (Jun 15)
- Re: pcap_inject() on loopback (FreeBSD) Fernando Gont (Jun 16)
- Re: pcap_inject() on loopback (FreeBSD) Guy Harris (Jun 16)
- Re: pcap_inject() on loopback (FreeBSD) Guy Harris (Jun 16)
- Re: pcap_inject() on loopback (FreeBSD) Fernando Gont (Jun 16)
- Re: pcap_inject() on loopback (FreeBSD) Guy Harris (Jun 15)