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/lib/ndb/fw names it, fw(8) uses it in two examples, and the service
file passes it as the rule file. Nothing provided it, so following any
of them got you a firewall that would not start.
Written for the qemu NAT segment this is developed on: the local /24
first, since the gateway and the resolver both live there, then name
resolution and the web, icmp so there is something to test with that
does not need a name resolved first, and one port answered on.
Calvin's; committed so the tree stops referring to a file that is not
in it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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The service file said -m /mnt/fw/ether0 and nothing made that name.
mntgen invents names one level deep, so the one over /mnt gives /mnt/fw
and stops there:
one mntgen over /mnt makes /mnt/fw yes
but not /mnt/fw/ether0, which is where fw is told to mount no
a second one over /mnt/fw does yes
So a second mntgen over /mnt/fw, as its own service, and every fw needs
it. It is a file server like the rest -- posts its name, lets the
process that started it exit -- so ready=srv:mntfw, the same shape fw
uses.
fwstart already does this imperatively, which is why the boot path
worked and the supervised path would not have. Four checks now pin the
premise both rest on, ending with fw actually mounting its control
files under the second mntgen.
The finding and the service file are Calvin's; the checks are mine.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Two things can happen when a firewall dies: the traffic it was
filtering carries on unfiltered, or it stops. Only the second is
defensible. A machine briefly off the network is a machine somebody
notices and fixes; a machine briefly on the network with no rules is
the thing the firewall was installed to prevent, and nobody notices it
at all.
fw already does the second, in all three modes, and by mechanism rather
than by care. Measured rather than assumed:
before fw device: /net/ether1 addr: 10.9.9.1 route: 10.9.9.254
fw running device: pkt0 addr: 10.9.9.1 route: 10.9.9.254
fw killed device: addr: route:
pktmedium is unbindonclose, so the interface and the address go when
fw's fds close, and the card is left bound to nothing with nothing
reading it. In a namespace it is harder still: /net answers "i/o on
hungup channel" and bind -a '#I' /net answers "mount/attach disallowed",
because the device mask was dropped before the program started.
So todo item 1 -- "a dead fw takes the network with it", open since the
first commit -- was the requirement written down as a defect. It is
now design.md and a FAILURE section in fw(8), and the tests assert it,
which is the point: this is exactly the property a later helpful change
reverses without meaning to. putback() was that change, written and
never run; deleting it removed a fail-open path, not just dead code.
What was actually broken is recovery, and in a way nobody had reached:
a fw that dies leaves its control filesystem mounted, and a corpse of a
mount fails everything asked of it -- including the access() check fw
makes before touching a card, which then refuses the restart:
fw: /tmp/rdbg/ctl: clone failed; not touching /net/ether1 until it exists
That check exists so fw does not take a card it cannot then serve, and
it was keeping fw from ever coming back. Now the dead mount is cleared
first, the same way reclaim() clears the pkt interface the same dead fw
left behind: both are its own wreckage.
With that and -a/-g in the service file -- so a restart does not need
the address it just lost -- the whole cycle works and never passes
through open: crash, network down, restart, network up and filtered.
Ten checks, three of which fail against the previous fw.c. 87 pass.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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todo.md said fw daemonizing meant svc could not supervise it, and that
it needed a foreground mode. Both wrong.
svc has had the shape from the start. ready=srv: watches the /srv name
rather than the pid, and its own manual says why: "Use this for a
service that posts to /srv and lets the process you started exit, which
many Plan 9 file servers do on purpose. For these the /srv file is
watched and the process is not, so the process exiting is normal and
never causes a restart." init.c agrees -- reap() returns early for
Ksrv with that comment on it.
Nor is detaching unusual. 42 commands under /sys/src/cmd use
postmountsrv or threadpostmountsrv; five call srv() directly, and every
one of those is a stdio server (ramfs -i, ext4srv -s, skelfs, hjfs,
wacom) speaking 9P on file descriptors it was handed. That is not a
foreground service, it is a pipe server: no /srv, no mount, nothing to
supervise. A foreground mode for fw would buy a pid to watch, and the
/srv name is the better signal -- it survives the process that made it.
What was true underneath the wrong diagnosis: the name was not honest.
Taking the control filesystem away ends the server proc, and the relays
carried on filtering:
procs: 3 ... take the ctl filesystem away ... procs after: 2
still filtering? pkt interface: pkt0
A firewall nobody can reach, stop, or notice, and the /srv name gone
while it runs. Srv.end now takes the whole thing down, which is the
answer the relays already gave when their wire failed. Same test after:
three procs become none and the interface goes with them.
So: no flag, an example service file in lib/svc, and a SUPERVISION
section in fw(8) that says what init should watch and what restarting
will and will not fix. Restart=always brings fw back; it does not undo
taking the card, so the new fw has no address to read. Supervision
works, recovery does not, and that stays open as item 1.
Two checks. Against the previous fw.c they fail with two orphaned
procs and a pkt interface still bound -- and so do the leak checks at
the end of the run, which is what they were built for. 77 pass.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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if(! test -d /mnt/fw)
mntgen /mnt/fw
mount(2) needs its mount point to exist, so mntgen cannot create
/mnt/fw -- and this ran it only when /mnt/fw was missing, which is
exactly the case where it fails:
mntgen: mount /tmp/mg/fw: file does not exist: '/tmp/mg'
So on a machine that had never had a /mnt/fw, the control directories
never appeared, and fw's own "not touching the card until the mountpoint
exists" check then refused every card in the file. The script has never
worked on a fresh machine. It has also never been run by the suite,
which is the other half of why nobody noticed.
Now the directory first, then mntgen only if it is not already there --
under mntgen every name exists, which is the test.
Both mntgen and fw leave a server behind, and a server started from a
shell keeps that shell's descriptors, so at boot they sit on the
console's input and it reads as a wedged terminal. This is the trap
CLAUDE.md documents; the script was walking into it. They get
/dev/null.
Three checks, and fwstart now gets run at all: a control directory
appears, a card that is not there is reported and skipped, and nothing
left running holds the descriptors we started it with. The first fails
against the old script. The third does not, because the old script
never started anything for want of the directory -- it guards the fix
from here, not the bug that was there.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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One program with three modes, sharing one rule engine and one ndb rule
language. Which mode it is depends on what you point it at, and it says
so at startup rather than choosing silently.
fw -e /net/ether0 rules.ndb a card: every packet in or out
fw rules.ndb <side> <side> two networks: everything crossing
fw rules.ndb one namespace: what programs ask for
The first two filter packets on a wire, using the pkt medium: the stack
gives up its card and gets a synthetic one with fw on the other end, so
nothing reaches it that fw did not pass. Since the stack no longer has
ethernet, fw answers ARP for the address it stands in for.
The third serves a filtered /net and matches connect and announce before
they reach the kernel, so a refusal comes back out of dial(2) with a
reason. That is only a boundary if the program also loses #I, which
/dev/drivers does and cannot be undone; fw.rc does it in the right order.
Rules are ndb, matched top to bottom, first match wins, no match denies.
Connections are tracked, so permitting traffic one way permits the
replies. A rule change drops connections the new rules forbid rather
than letting them finish: a block blocks. Logging is per rule, to
/sys/log/fw.
Tested on the init-test VM in all three modes: a page fetched through a
real card, a TCP handshake across two networks, request filtering with
the escape routes closed, live rule changes killing established
connections, and one rule file working unchanged at both altitudes.
doc/todo.md has what is not done. Item 1 is the one that matters: a fw
that dies takes the card's address with it, so the machine loses its
network and fw cannot restart unaided. That also blocks svc supervision.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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