diff options
Diffstat (limited to 'fw/test')
| -rw-r--r-- | fw/test/rawether.c | 97 | ||||
| -rw-r--r-- | fw/test/wire.md | 105 |
2 files changed, 202 insertions, 0 deletions
diff --git a/fw/test/rawether.c b/fw/test/rawether.c new file mode 100644 index 0000000..540d0b6 --- /dev/null +++ b/fw/test/rawether.c @@ -0,0 +1,97 @@ +/* + * rawether - put one ethernet frame on the wire, addressed as told. + * + * A stack will only ever address a frame to the mac it resolved, so a + * frame addressed to somebody else has to be forged. That is the only + * way to ask a firewall on a card whether it is looking at frames that + * are not for it. + * + * rawether /net/ether1 <dstmac> <srcip> <dstip> + * + * The payload is an icmp echo request, which is enough to be counted. + */ +#include <u.h> +#include <libc.h> +#include <ip.h> + +enum { Ehdrlen = 14, Eminlen = 60, Etip4 = 0x0800 }; + +static ushort +csum(uchar *p, int n) +{ + ulong s; + int i; + + s = 0; + for(i = 0; i+1 < n; i += 2) + s += (p[i]<<8) | p[i+1]; + if(i < n) + s += p[i]<<8; + while(s >> 16) + s = (s & 0xFFFF) + (s >> 16); + return ~s; +} + +void +main(int argc, char **argv) +{ + uchar f[Eminlen], dst[6], src[6], sip[IPaddrlen], dip[IPaddrlen]; + char path[128], buf[64]; + int cfd, dfd, n, conn; + + if(argc != 5){ + fprint(2, "usage: rawether /net/etherN dstmac srcip dstip\n"); + exits("usage"); + } + if(parseether(dst, argv[2]) < 0) + sysfatal("%s: bad ethernet address", argv[2]); + if(parseip(sip, argv[3]) == -1 || parseip(dip, argv[4]) == -1) + sysfatal("bad ip address"); + + snprint(path, sizeof path, "%s/clone", argv[1]); + if((cfd = open(path, ORDWR)) < 0) + sysfatal("open %s: %r", path); + if((n = read(cfd, buf, sizeof buf - 1)) <= 0) + sysfatal("read %s: %r", path); + buf[n] = '\0'; + conn = atoi(buf); + if(fprint(cfd, "connect -1") < 0) + sysfatal("connect -1: %r"); + snprint(path, sizeof path, "%s/%d/data", argv[1], conn); + if((dfd = open(path, ORDWR)) < 0) + sysfatal("open %s: %r", path); + snprint(path, sizeof path, "%s/addr", argv[1]); + if((n = open(path, OREAD)) < 0) + sysfatal("open addr: %r"); + if(read(n, buf, 12) != 12) + sysfatal("read addr: %r"); + close(n); + buf[12] = '\0'; + if(parseether(src, buf) < 0) + sysfatal("unparseable card address %s", buf); + + memset(f, 0, sizeof f); + memmove(f, dst, 6); + memmove(f+6, src, 6); + f[12] = Etip4 >> 8; + f[13] = Etip4; + + f[14] = 0x45; /* v4, 20 byte header */ + hnputs(f+16, 28); /* total length */ + f[22] = 64; /* ttl */ + f[23] = 1; /* icmp */ + memmove(f+26, sip+IPv4off, 4); + memmove(f+30, dip+IPv4off, 4); + hnputs(f+24, csum(f+14, 20)); + + f[34] = 8; /* echo request */ + hnputs(f+38, 0x1234); /* id */ + hnputs(f+40, 1); /* seq */ + hnputs(f+36, csum(f+34, 8)); + + if(write(dfd, f, sizeof f) != sizeof f) + sysfatal("write: %r"); + fmtinstall('E', eipfmt); + print("sent %d bytes to %E\n", (int)sizeof f, dst); + exits(nil); +} diff --git a/fw/test/wire.md b/fw/test/wire.md new file mode 100644 index 0000000..b4494f3 --- /dev/null +++ b/fw/test/wire.md @@ -0,0 +1,105 @@ +# Testing fw on a wire + +`fwtest.rc` runs on one machine and can go no further than the card: it +can take a spare one and watch what fw does to the interfaces, but it +cannot make a neighbour send anything. Everything past that — ARP +against something that will answer, real traffic being filtered, frames +addressed to somebody else — needs a second machine on the same +segment. + +`run.sh` will build one. `-gw` listens, `-lan` connects, and qemu joins +the two into a point-to-point ethernet segment the host is not on. The +LAN card is `ether1` on both. + + ./newvm.sh peer + ./run.sh -headless -gw init-test.qcow2 & + ./run.sh -headless -lan peer.qcow2 & + +The peer can be a plain overlay of the base: it needs no fw, only an +address. Both cards must have distinct ethernet addresses, which +`run.sh` derives from the VM name — before it did that, every guest had +qemu's default and two machines on one segment shared a MAC, which is +invisible point-to-point and makes every check below meaningless. + +## The rig + +On the firewall machine, a stack of its own so the real network is +untouched, and fw on the spare card: + + bind -a '#l1' /net + bind -a '#I63' /tmp/nW + @{ conv=`{cat /fd/0} + echo -n 'bind ether /net/ether1' >[1=0] + echo -n 'add 10.9.9.1 255.255.255.0' >[1=0] } <>[0] /tmp/nW/ipifc/clone + echo 'allow=in proto=icmp' > /tmp/r.ndb + fw -s fw.wire -n /tmp/nW -e /net/ether1 -m /tmp/ctl /tmp/r.ndb \ + </dev/null >/dev/null >[2]/dev/null + +`-s` matters: fw's control files are otherwise only reachable through +the mount in the namespace that started it, and that namespace is gone +by the time you want to look. With a `/srv` name any shell can +`mount /srv/fw.wire /tmp/wctl`. + +Redirect all three descriptors. fw daemonizes, so anything that leaves +it holding a pipe — `fw ... | grep`, or a command substitution around +it — waits for a firewall that is not going to exit. + +On the peer, the other end of the segment: + + bind -a '#l1' /net + bind -a '#I64' /tmp/np + @{ conv=`{cat /fd/0} + echo -n 'bind ether /net/ether1' >[1=0] + echo -n 'add 10.9.9.2 255.255.255.0' >[1=0] } <>[0] /tmp/np/ipifc/clone + rfork n; bind /tmp/np /net + +## What it shows + +**ARP for an address whose card has been taken.** Nothing else is +answering for 10.9.9.1 — the stack that owns it has a `pkt` interface +and no ethernet — so if `ip/ping 10.9.9.1` works at all, fw answered. +The peer's `/net/arp` says whose: + + ether OK 10.9.9.1 52540087c8c1 10.9.9.2 + +which is the firewall's *card*, not the peer's own. The first ping +takes about a second and the rest are sub-millisecond: fw has to ARP +for the peer before it can send the reply, and drops the first one +while it asks. That is the one drop no rule caused, in fw(8) BUGS. + +**Filtering, as against forwarding.** With `allow=in proto=icmp` alone, +a TCP connect from the peer sits for 290 seconds and gives up: + + connection timed out + +Add the rule through the running firewall and the same connect answers +in 2 seconds: + + echo -n 'prepend allow=in proto=tcp lport=17019' > /tmp/wctl/ctl + connection refused + +"Refused" is the far stack's RST, so the packet arrived; "timed out" is +fw dropping it silently. That difference is the whole point of the +program, and it is the only way to see it from outside. + +**Frames addressed to somebody else.** A stack only ever addresses a +frame to the MAC it resolved, so this one has to be forged: +`rawether.c`, in this directory, writes a single frame with whatever +destination you name. + + rawether /net/ether1 52540087c8c1 10.9.9.2 10.9.9.1 # fw's card + rawether /net/ether1 525400aabbcc 10.9.9.2 10.9.9.1 # nobody's + +Watch `passed` in `/tmp/wctl/stats` across each. The card is +promiscuous and has to be, so both frames arrive — a promiscuous reader +on the firewall machine sees both, which is worth confirming first, or +a frame that never arrived looks exactly like one that was filtered: + + 52 54 00 aa bb cc 52 54 00 37 df 23 08 00 45 00 + +With the destination check in `etherin`, the second frame moves nothing. +Without it, both move the counter by the same amount: + + to fw's card to nobody's + no check +3 +3 + with the check +2 0 |