Previously, such queries would all be forwarded
independently. This is, in theory, inefficent but in practise
not a problem, _except_ that is means that an answer for any
of the forwarded queries will be accepted and cached.
An attacker can send a query multiple times, and for each repeat,
another {port, ID} becomes capable of accepting the answer he is
sending in the blind, to random IDs and ports. The chance of a
succesful attack is therefore multiplied by the number of repeats
of the query. The new behaviour detects repeated queries and
merely stores the clients sending repeats so that when the
first query completes, the answer can be sent to all the
clients who asked. Refer: CERT VU#434904.
Use the SHA-256 hash function to verify that DNS answers
received are for the questions originally asked. This replaces
the slightly insecure SHA-1 (when compiled with DNSSEC) or
the very insecure CRC32 (otherwise). Refer: CERT VU#434904.
At any time, dnsmasq will have a set of sockets open, bound to
random ports, on which it sends queries to upstream nameservers.
This patch fixes the existing problem that a reply for ANY in-flight
query would be accepted via ANY open port, which increases the
chances of an attacker flooding answers "in the blind" in an
attempt to poison the DNS cache. CERT VU#434904 refers.
Hi Simon,
> Add --shared-network config. This enables allocation of addresses
> the DHCP server in subnets where the server (or relay) doesn't
> have an interface on the network in that subnet. Many thanks to
> kamp.de for sponsoring this feature.
Does this paragraph lack a preposition "by" early on the 2nd line, or am
I mis-guessing the purpose?
...enables allocation of addresses *by* the DHCP server...
The manual page also seems to offer room for linguistic improvement
(apparently written by a German, so I see the typical patterns, and also
the misuse of which vs. that.
I am attaching a patch series vs. git to fix several issues in the
manpage and CHANGELOG.
From 35b88d98429e2fe016d9989d220f6faf2b933764 Mon Sep 17 00:00:00 2001
From: Matthias Andree <matthias.andree@gmx.de>
Date: Sun, 5 Apr 2020 11:18:05 +0200
Subject: [PATCH 1/5] man/dnsmasq.8: Properly capitalize DHCP acronym.
When a request matching the clid or mac address is
recieved the server will iterate over all candidate
addresses until it find's one that is not already
leased to a different clid/iaid and advertise
this address.
Using multiple reservations for a single host makes it
possible to maintain a static leases only configuration
which support network booting systems with UEFI firmware
that request a new address (a new SOLICIT with a new IA_NA
option using a new IAID) for different boot modes, for
instance 'PXE over IPv6', and 'HTTP-Boot over IPv6'. Open
Virtual Machine Firmware (OVMF) and most UEFI firmware
build on the EDK2 code base exhibit this behaviour.
The idea of this option was already discussed years ago on the mailing
list:
https://dnsmasq-discuss.thekelleys.org.narkive.com/ZoFQNaGo/always-ignore-client-identifier#post4
In our production environnement, we discovered that some devices are
using 'client identifier' not unique at all, resulting on IP addresses
conflicts between several devices (we saw up to four devices using same
IP address).
The root cause is probably a buggy operating system/configuration of
decices, but this patch add a configuration workaround on server side
when fixing clients is impossible.
Signed-off-by: Charles Daymand <charles.daymand@wifirst.fr>
Signed-off-by: Florent Fourcot <florent.fourcot@wifirst.fr>
In a reply proving that a DS doesn't exist, it doesn't matter if RRs
in the auth section _other_ than NSEC/NSEC3 are not signed. We can't
set the AD flag when returning the query, but it still proves
that the DS doesn't exist for internal use.
As one of the RRs which may not be signed is the SOA record, use the
TTL of the NSEC record to cache the negative result, not one
derived from the SOA.
Thanks to Tore Anderson for spotting and diagnosing the bug.
In an era where everything has an MMU, this looks like
an anachronism, and it adds to (Ok, multiplies!) the
combinatorial explosion of compile-time options.
For ease of implementaion, dnsmasq has always forked a new process to
handle each incoming TCP connection. A side-effect of this is that any
DNS queries answered from TCP connections are not cached: when TCP
connections were rare, this was not a problem. With the coming of
DNSSEC, it's now the case that some DNSSEC queries have answers which
spill to TCP, and if, for instance, this applies to the keys for the
root then those never get cached, and performance is very bad. This
fix passes cache entries back from the TCP child process to the main
server process, and fixes the problem.
Change anti cache-snooping behaviour with queries with the
recursion-desired bit unset. Instead to returning SERVFAIL, we
now always forward, and never answer from the cache. This
allows "dig +trace" command to work.
Dnsmasq does pass on the do-bit, and return DNSSEC RRs, irrespective
of of having DNSSEC validation compiled in or enabled.
The thing to understand here is that the cache does not store all the
DNSSEC RRs, and dnsmasq doesn't have the (very complex) logic required
to determine the set of DNSSEC RRs required in an answer. Therefore if
the client wants the DNSSEC RRs, the query can not be answered from
the cache. When DNSSEC validation is enabled, any query with the
do-bit set is never answered from the cache, unless the domain is
known not to be signed: the query is always forwarded. This ensures
that the DNSEC RRs are included.
The same thing should be true when DNSSEC validation is not enabled,
but there's a bug in the logic.
line 1666 of src/rfc1035.c looks like this
if ((crecp->flags & (F_HOSTS | F_DHCP | F_CONFIG)) || !do_bit || !(crecp->flags & F_DNSSECOK))
{ ...answer from cache ... }
So local stuff (hosts, DHCP, ) get answered. If the do_bit is not set
then the query is answered, and if the domain is known not to be
signed, the query is answered.
Unfortunately, if DNSSEC validation is not turned on then the
F_DNSSECOK bit is not valid, and it's always zero, so the question
always gets answered from the cache, even when the do-bit is set.
This code should look like that at line 1468, dealing with PTR queries
if ((crecp->flags & (F_HOSTS | F_DHCP | F_CONFIG)) ||
!do_bit ||
(option_bool(OPT_DNSSEC_VALID) && !(crecp->flags & F_DNSSECOK)))
where the F_DNSSECOK bit is only used when validation is enabled.
