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/net/tcp/trans, /net/udp/trans and /net/icmp/trans install kernel
address translations. devip gates them with iseve() (devip.c:406), and
through this server that is fw's identity, not the caller's -- fw does
every open with its own credentials and never looks at the client's. On
a machine where fw runs as eve, which is the ordinary case, there was no
gate at all. Demonstrated in a sandbox with an empty rule set:
=== baseline: real /net, no fw ===
echo: write error: local ip not found
=== inside the sandbox ===
connect: refused (as expected)
append via fw: local ip not found
create via fw: bad process or channel control request
Both errors come from transwrite itself, so the open succeeded and fw
imposed nothing; and the second proves the OTRUNC path is reachable,
which runs transwrite(p, nil, 0, 0) and flushes the whole table before
the write is even parsed.
/net/log was half closed: the write was refused so a program could not
turn tracing on, but reading it was the leak, and anything an
administrator turns on elsewhere is then readable from inside the
sandbox. ipifc data was refused rather than hidden, against the
principle stated ten lines above it for ether and ipmux, and its snoop
file is the same wire and was not mentioned at all.
The pattern is the problem. A list of things to deny has now been wrong
twice, in the same way the ctl filter was, and the answer is the one
that worked there: nothing is served unless it is named. Protocol
directories come from a list of names rather than from "has a clone
file", because devether has one of those too and #l bound into /net
would have become a protocol; a protocol missing from the list is one
nobody can reach, which is the safe way to be out of date. Within one,
only clone, stats and the conversation files, and for ipifc not clone,
not data, not snoop. In the root, only cs and dns writable and arp,
bootp, iproute, ipselftab and ndb readable.
Splitting the path also disposes of a name like "tcp/../.." arriving as
a single walk element from a client speaking 9P straight to the server:
more than three components, or an empty one, is not a path this server
handed out, so it is not one it will honour.
Sixteen new checks. Against the previous netfs.c six of them fail --
trans served, log served, ipifc data and snoop served, and both listing
checks -- while cs, arp, ndb, iproute, ipifc status, clone and connect
filtering all still pass, which is the half that matters. They ask by
stat rather than by read: reading log or a data file blocks until
traffic arrives, so reading would hang on exactly the build that still
serves them, and a test that hangs on a regression is worse than none.
46 pass, twice in a row with no cleanup between.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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The serious one is that the ctl filter was a blacklist. checkctl looked
at connect and announce and passed everything else, but udpctl takes
"headers", and udpcreate gives a conversation a live write queue at clone
time:
c->wq = qbypass(udpkick, c);
So three writes -- clone, "headers", a header-prefixed datagram to data --
sent a packet anywhere, with no connect for a rule to match. rudp and
icmpv6 have the same verb, gre has raw and forward. none.ndb did not
mean "no network at all", though the manual said it did. It is now a
whitelist of control messages that cannot reach the network by
themselves, which is the argument this code already made about ndb
attributes it does not recognise, applied where it was not.
Also blocking: %M was never installed, so fmtrules emitted ipmask=%M% and
every ctl edit on a rule set containing ip= failed, while save wrote a
file reload would reject. Tests had exercised the ctl path and the ip=
path but never together.
parserules built the new list in the globals with no lock, so for the
length of a reload the relay procs walked a list that was empty and then
half built -- exactly what installrules' comment promised could not
happen. etherwriteip put a 64KB frame on a 32KB proc stack, the same bug
design.md records learning and fixing in relay(). putback and
notehandler were dead code: atexit matches on the registering pid and
_exits never runs the handlers, which is why the cleanup "did not fire"
rather than being flaky. Nothing puts the card back, and the docs that
said otherwise are corrected.
The rest: expired flows kept matching and refreshing themselves; the pkt
interface claimed a 4096 MTU from a 1514-byte card; ports were read out
of non-first fragments; /net/ndb and /net/log were writable and
ipifc/*/data readable through the filter; control files were
world-writable, and owning them as a user called "fw" locked out the
administrator instead; delete 0 appended a rule reading <nil>; a dead
relay left one direction unfiltered with nothing to notice; and IPv6
unicast under -e was dropped in silence when it is simply not
implemented.
All three modes regression tested after: a namespace refusing headers and
port 22 while allowing 443, a card passing https and then blocking it
live, and the machine's network restored afterwards.
doc/todo.md says which of these were reproduced and which were read.
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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