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learnaddr, reclaim and takecard each read a status or route file into a
fixed 1024-byte buffer and split it into at most eight lines. I called
this a defect that could lose the default route. It could not: routes
come out sorted, and 0.0.0.0 sorts first, so the default route is on
the first line of the table and both limits are reached long after it
has been found. The report was wrong about the consequence.
The limits are still worth removing, and one thing in there was a real
mistake: learnaddr and takecard looked for the device name anywhere in
the status text, addresses included, rather than in the field that
holds it. An interface whose address contained the name of the device
being looked for would have matched. Contrived, but there is no reason
to be searching a blob for something that has a place of its own. Bio
reads line by line, the device is matched against the device field, and
nothing has a length limit any more.
More to the point, none of this had ever been run. Card mode is
outside the suite because taking the machine's card away is how you
end up with no network -- but a second card that nothing is using can
be taken safely. The suite now binds #l1 into /net, puts it in an IP
stack of its own with an address and a default route, and hands it to
fw with no -a and no -g:
fw: /net/ether1 has 10.9.9.1/120, gateway 10.9.9.254
fw: took /net/ether1 away from .../ipifc/0
fw: protected .../ipifc/0 addr 10.9.9.1 /120
fw: default route via 10.9.9.254
Six checks on that: the address and gateway are read off the interface
rather than repeated on the command line, the card is taken, what
replaces it is a pkt interface at the card's mtu holding the same
address, and the route the card carried is put back. Skipped when
there is no spare card, which is why it says so rather than passing
quietly. 72 pass.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Only the first fragment of a datagram carries the transport header, so
every later one matched no port, and a rule set written in ports --
which is every rule set in fwrules(6) -- denied it. Measured, 3000
bytes of UDP over a 1500 mtu, against a rule permitting the port:
passed 1
dropped 2
The first fragment crossed and the receiver waited for the rest until
it gave up. The alternative this replaced was worse: reading ports out
of a later fragment lets one whose payload bytes happen to look like an
open connection through, which is a firewall evasion older than most
firewalls.
So the first fragment decides and the rest of the train inherits. The
train is what the receiving stack reassembles on -- protocol,
addresses, identification -- and lasts about as long as that stack will
hold the pieces. A train whose head we never saw is judged on its
addresses alone, and so is normally denied: it is either an attack or
the tail of a datagram we already refused. Same measurement after:
passed 3
dropped 0
and one rule decision for the datagram rather than one per fragment.
IPv6 fragments live in an extension header, which fw does not walk, so
none of this reaches them; that stays in BUGS.
Four checks, three of which fail against the previous fw.c. The fourth
-- the far stack's own InDatagrams -- is read as a difference across
the exchange, not a total: an IP stack outlives the run that made it,
and reading the total made the check pass on a build that had dropped
two thirds of the datagram.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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relay() and permitted() were the same twenty lines twice: parse, work
out which end is the peer, consult the flow table, consult the rules,
log, count, remember. Two copies that had already drifted -- relay
printed "(state)" and "(new)" under -d and permitted printed neither,
and the two spelled the drop reason differently -- and every fix since
has had to be made in both, which is how the copies drift further.
Now relay reads a packet, asks permitted, and writes it or does not.
The debug line permitted was missing is added rather than dropped, so
-d still distinguishes a packet the flow table let through from one the
rules did.
No new checks: the point is that nothing changes. The gateway tests
already cover this path -- a connection crossing, one rule serving both
directions, a rule change killing a live flow -- and all 60 pass.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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fmtrules formatted into a 64K buffer with seprint, which clamps, and
returned how much it had written. Nothing looked at whether that was
everything. Since prepend, append and delete all work by formatting
the whole set out, editing the text and parsing it back -- deliberately,
so that a rule typed at ctl and a rule in a file go through one parser
-- editing a set past the limit did not truncate the display, it
truncated the rules.
Measured with 2000 rules, about 104K formatted:
and all of it comes back want: 2000 got: 1214
and survives an edit want: ok got: refused
with nothing lost off the end got: 1214
786 rules gone from the running firewall, and the only sign is that the
edit after it failed. save wrote the same short file, so reload would
then have made the loss permanent.
Now sized and allocated to fit. The bound is per rule -- the fixed
attributes at their longest, plus the protocol, which is the only part
whose length is ndb's choice rather than ours -- summed under the same
lock that formats, so an install cannot get between the two passes.
flows had the identical cap and gets the identical fix; on a busy
firewall it is the file most likely to reach it. Rulebuf is gone.
Six checks: a 2000-rule set loads, comes back whole, survives an edit,
and saves whole.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Three findings, one interface. matchrule handed back a Rule* and a
pointer into a static char[128], both read by the caller after it had
released rulelock:
e = matchrule(verb, ..., &rule);
if(rule != nil && rule->log) /* freed? */
syslog(0, "fw", "... %s", e); /* whose? */
A rule set installed between the return and those two lines frees the
Rule under them, which is a narrow window but this is a firewall, and
two procs deciding at once overwrite each other's reason -- in a program
whose entire output is the reason. netfs.c ran multi-proc from the
first blocking open and had its own static err with the same problem.
Neither is a race you can test for; both stop existing if the answer
lives in the caller's frame, so it does. Seven positional arguments
become named fields while the signature is being rewritten anyway.
The third is that revalidate could not ask without being counted. A
rule edit rebuilds the set, so every hit count starts at zero, and then
revalidate re-checks each live flow against the new rules and charged
every one of them to the rule that matched. So a rule that had decided
nothing since the edit reported one decision per live connection, and
stats answered a different question after every edit. count says
whether this is traffic.
Also: the log said "deny tcp connect 127.0.0.2" for a connection to a
port it never named. getfields writes over the separators it splits
on, so f[1] afterwards is only what precedes the first "!". The
address is copied before it is taken apart.
Four checks. Two exercise the log path end to end, denied and
permitted, matching the full address and the rule number in
/sys/log/fw -- which they create if it is missing and remove again if
they made it. One reads the hit count after an edit: with count put
back to 1 in revalidate it reports 1 where 0 is right. 51 pass.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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todo.md had three items in both halves of itself. Control files being
world-writable, delete 0, and a dead relay leaving half a firewall were
all in "Fixed since the review" as items 10, 11 and 12, and all three
were still sitting in "Worth fixing" underneath. Anyone working the
open list would have redone them. Now an item appears in one half or
the other, and the first round's entries are one line each, since the
detail is in the commit and the value of this file is the part that is
still true.
Fragments got a sentence that described the mechanism and not the
consequence. "Later fragments now match on addresses and protocol
only" reads as though they would pass under an address rule; what
actually happens is that every rule set in fwrules(6) is written in
ports, later fragments match no port, and the datagram does not cross.
That is the right trade against reading ports out of them, which let a
crafted fragment through, but it is a hole in what works and belongs in
BUGS rather than in a changelog line.
man/fw also now says what the served /net contains, which changed
underneath it and was never written down; and it still said the card
was "not undone reliably", when nothing undoes it at all.
design.md gains the whitelist decision next to the others, because the
argument for it is the same one the rule parser already makes and the
next person to add a file to the served tree should meet it.
The mtu comment claimed a card as its reason while sitting in code both
modes use. Between two stacks there is no card; 1500 is still right,
for a reason worth one sentence.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Maxframe was Ehdrlen + 16K, an automatic in etherwriteip, which runs on
a proc created with a 32K stack. It fits, and the previous fix was
right that 64K did not, but half a stack for a buffer that -- since the
pkt interface is now told "mtu 1500" -- can never hold more than 1514
bytes is a number waiting to be wrong again, and libthread allocates
that stack with malloc, so being wrong means quietly corrupting the
heap rather than faulting.
So the buffer belongs to the caller, with its size, and the guard is
against that size. etherout allocates it once, from the same Maxpkt it
sizes its read buffer with, which is the only place that knows how much
can arrive. ether.c no longer has a length of its own to drift.
The IPv6 message now also goes to syslog. fw daemonizes, so a message
on file descriptor 2 goes wherever the shell that started it was
pointing, which for a firewall started at boot is nowhere.
No test. etherwriteip is reached only in card mode, which the suite
stays out of on purpose because a test that can leave the machine with
no network is a test nobody runs. A unit harness for ether.c -- point
efd at a pipe, call etherwriteip, read the frame back -- would cover
this and the broadcast mapping that todo.md still records as written
but never observed. Worth doing; not done here.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Two warnings have stood in fw.c since the program was written:
warning: fw.c:732 auto declared and not used: buf
warning: fw.c:1286 set and not used: m
Neither matters on its own -- an unused array in fsread, and an m = nil
that the next line overwrites -- but a build that always prints two
warnings is a build whose output nobody reads, which is how the next
one that does matter goes unnoticed. Both are the sort of thing kencc
tells you for free.
So the suite now builds the source from clean and asks the compiler
whether it had anything to say. Reintroducing the unused array makes
it fail with the warning printed under the check, which is what a
finding nobody had to look for should look like. It also checks that
mk succeeded, since a build that does not run produces no warnings
either. Skipped if the source is not on the machine being tested.
48 pass.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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The last round removed the two call sites and said the code was gone.
It was not: putback, notehandler and the five back* globals were still
there with no callers, and the comment that was meant to be moved back
to reclaim() was copied instead, so the file carried the same twelve
lines twice in a row above a function they do not describe. kencc does
not warn about an unused static function, so nothing objected.
Dead code that reads like a safety net is worse than none. Anyone
finding putback() would reasonably conclude the card is restored on the
way out; it is not, and the reason is in the comment that now stands
where the duplicate was, so the next person to look does not have to
re-derive atexit's pid matching to find out why.
Also moves netfs.c's "connect takes addr!port" comment down to checkctl,
which it describes, from above the okverbs table, which it does not.
No test: the deletion is invisible at runtime, which is the whole
complaint about it. The suite still passes 46, and card mode -- the
only thing putback ever touched -- is deliberately outside it.
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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