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dns/dnsmasq: fix rare cache corruption problem

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Simon Kelley sent an advisory that in rare circumstances, the cache can
become corrupted and the DNS subsystem then became disfunctional.
This is reported as regression in 2.88.
Chances seem higher this happens with DNSSEC enabled, but seems not limited
to it.  For details, please see the patch contained in this commit, or
https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2023q1/016821.html

The symptom of this happening is apparently a cache internal error.

2.89 with this fix and a few others is slated for release in a week.
Let's fix the patch already and MFH to 2023Q1 so we keep our liberties
to decide whether we need to move quarterly to 2.89 or rather stick
with 2.88_1.

originally
Reported by:	Timo van Roermund (to Simon Kelley in private)
Reported by:	Simon Kelley (upstream maintainer, through mailing list)
Obtained from:	Simon Kelley (upstream maintainer, Git repository)
MFH:		2023Q1

(cherry picked from commit 038ffa5e63)
This commit is contained in:
Matthias Andree 2023-01-14 10:10:42 +01:00
parent abc7dd2d59
commit cd6957878c
2 changed files with 86 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
dns/dnsmasq/Makefile
View File

@ -1,7 +1,7 @@
PORTNAME= dnsmasq
DISTVERSION= 2.88
# Leave the PORTREVISION in even if 0 to avoid accidental PORTEPOCH bumps:
PORTREVISION= 0
PORTREVISION= 1
PORTEPOCH= 1
CATEGORIES= dns
MASTER_SITES= https://www.thekelleys.org.uk/dnsmasq/ \

85
dns/dnsmasq/files/patch-zgf172fdb Normal file
View File

@ -0,0 +1,85 @@
From f172fdbb77c422e27d3b7530f3fe95b98d1608e7 Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Wed, 11 Jan 2023 23:23:40 +0000
Subject: [PATCH] Fix bug which can break the invariants on the order of a hash
chain.
If there are multiple cache records with the same name but different
F_REVERSE and/or F_IMMORTAL flags, the code added in fe9a134b could
concievable break the REVERSE-FORWARD-IMMORTAL order invariant.
Reproducing this is damn near impossible, but it is responsible
for rare and otherwise inexplicable reversion between 2.87 and 2.88
which manifests itself as a cache internal error. All observed
cases have depended on DNSSEC being enabled, but the bug could in
theory manifest itself without DNSSEC
Thanks to Timo van Roermund for reporting the bug and huge
efforts to isolate it.
---
CHANGELOG | 16 +++++++++++++++-
src/cache.c | 14 +++++++++-----
2 files changed, 24 insertions(+), 6 deletions(-)
diff --git a/CHANGELOG b/CHANGELOG
index 0f36a0f..d6e6753 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,20 @@
+version 2.98
+ Fix bug introduced in 2.88 (commit fe91134b) which can result
+ in corruption of the DNS cache internal data structures and
+ logging of "cache internal error". This has only been seen
+ in one place in the wild, and it took considerable effort
+ to even generate a test case to reproduce it, but there's
+ no way to be sure it won't strike, and the effect to to break
+ the cache badly. Installations with DNSSEC enabled are more
+ likely to see the problem, but not running DNSSEC does not
+ guarantee that it won't happen. Thanks to Timo van Roermund
+ for reporting the bug and for his great efforts in chasing
+ it down.
+
+
version 2.88
Fix bug in --dynamic-host when an interface has /16 IPv4
- address. Thanks to Mark Dietzer for spotting this.
+ address. Thanks to Mark Dietzer for spotting this.
Add --fast-dns-retry option. This gives dnsmasq the ability
to originate retries for upstream DNS queries itself, rather
diff --git a/src/cache.c b/src/cache.c
index 42283bc..0a5fd14 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -236,19 +236,23 @@ static void cache_hash(struct crec *crecp)
char *name = cache_get_name(crecp);
struct crec **up = hash_bucket(name);
-
- if (!(crecp->flags & F_REVERSE))
+ unsigned int flags = crecp->flags & (F_IMMORTAL | F_REVERSE);
+
+ if (!(flags & F_REVERSE))
{
while (*up && ((*up)->flags & F_REVERSE))
up = &((*up)->hash_next);
- if (crecp->flags & F_IMMORTAL)
+ if (flags & F_IMMORTAL)
while (*up && !((*up)->flags & F_IMMORTAL))
up = &((*up)->hash_next);
}
- /* Preserve order when inserting the same name multiple times. */
- while (*up && hostname_isequal(cache_get_name(*up), name))
+ /* Preserve order when inserting the same name multiple times.
+ Do not mess up the flag invariants. */
+ while (*up &&
+ hostname_isequal(cache_get_name(*up), name) &&
+ flags == ((*up)->flags & (F_IMMORTAL | F_REVERSE)))
up = &((*up)->hash_next);
crecp->hash_next = *up;
--
2.20.1