Created attachment 153698 [details]
Check for pseudo_AF_HDRCMPLT to allow tcpreplay on loopback

Capturing a pcap file for loopback/null encapsulation and then replaying with tcpreplay doesn't work.

Reproduce:

* Capture a trace on lo0 e.g.   tcpdump -i lo0 -s 0 -n -w loopback.pcap
* echo "bla" | nc localhost 1234
* Stop the capture. It has two packages.. the UDP message and ICMP
* Install tcpreplay with pkg install tcpreplay
* Monitor loopback for traffic tcpdump -i lo0 -s 0 -n -X
* Replay with tcpreplay --intf1=lo0 loopback.pcap

Expectation:
* Replayed packets arriving on the loopback device

Outcome:
* $ dmesg
looutput: af=31 unexpected
looutput: af=31 unexpected

Reason:

tcpreplay is using libpcap for replay and is setting the complete header field

open("/dev/bpf0",O_RDWR,00)			 = 3 (0x3)
ioctl(3,BIOCVERSION,0xbfbfe7c8)			 = 0 (0x0)
ioctl(3,BIOCSETIF,0xbfbfe7d0)			 = 0 (0x0)
ioctl(3,BIOCGDLT,0xbfbfe7c4)			 = 0 (0x0)
ioctl(3,BIOCSHDRCMPLT,0xbfbfe7c0)		 = 0 (0x0)
ioctl(3,BIOCGDLT,0xbfbfe808)			 = 0 (0x0)


This means that in bpf.c:bpfwrite

        if (d->bd_hdrcmplt)
                dst.sa_family = pseudo_AF_HDRCMPLT;

will be executed but in if_loop.c:looutput
        /* 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;

will be checked. This means that the local variable "af" will contain pseudo_AF_HDRCMPLT which is not handled in the switch.

Proposal. Change the check from AF_UNSPEC to pseudo_AF_HDRCMPLT or at least check for pseudo_AF_HDRCMPLT as well.