Good catch!
I've understood and reproduced this now, and I'm happy that the patch
fixes it..
I've committed the patch, and tagged 2.91rc6. I'd hoped to release 2.91
today, but I'll give it a few days with this and some other fixes before
doing that.
Cheers,
Simon.
On 3/13/25 13:52, Tijs Van Buggenhout via Dnsmasq-discuss wrote:
Hi Simon,
This is a regression. When dnsmasq is started without upstreams (yet), but a
DNS query comes in that needs forwarding dnsmasq now potentially crashes as
the value for "first" variable is undetermined.
A segmentation violation occurs when the index is out of bounds of
serverarray.
(gdb) run -d --log-queries --log-debug -R
Starting program: /var/tmp/git/dnsmasq/src/dnsmasq -d --log-queries --log-
debug -R
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
dnsmasq: started, version 2.91rc5-2-ge427d4b cachesize 150
dnsmasq: compile time options: IPv6 GNU-getopt no-DBus no-UBus no-i18n no-IDN
DHCP DHCPv6 no-Lua TFTP no-conntrack ipset no-nftset auth no-DNSSEC loop-
detect inotify dumpfile
dnsmasq: warning: no upstream servers configured
dnsmasq: read /etc/hosts - 42 names
dnsmasq: *** log_query_mysockaddr: IN
dnsmasq: query[A] freshtomato.org from 127.0.0.1
dnsmasq: *** forward_query: IN
dnsmasq: *** forward_query: new query
dnsmasq: *** forward_query: if (!lookup_domain())
dnsmasq: *** forward_query: before master =
dnsmasq: *** forward_query: first=[-8080]
Program received signal SIGSEGV, Segmentation fault.
0x0000555555578c83 in forward_query (udpfd=udpfd@entry=4,
udpaddr=udpaddr@entry=0x7fffffffe180, dst_addr=dst_addr@entry=0x7fffffffe160,
dst_iface=dst_iface@entry=1, header=header@entry=0x5555555be2f0,
plen=plen@entry=56, replylimit=1232, now=1741871839, forward=0x0,
fwd_flags=160, fast_retry=0) at forward.c:398
398 master = daemon->serverarray[first];
(gdb) bt
#0 0x0000555555578c83 in forward_query (udpfd=udpfd@entry=4,
udpaddr=udpaddr@entry=0x7fffffffe180, dst_addr=dst_addr@entry=0x7fffffffe160,
dst_iface=dst_iface@entry=1, header=header@entry=0x5555555be2f0,
plen=plen@entry=56,
replylimit=1232, now=1741871839, forward=0x0, fwd_flags=160, fast_retry=0)
at forward.c:398
#1 0x0000555555579c27 in receive_query (listen=<optimized out>,
now=now@entry=1741871839) at forward.c:2053
#2 0x000055555557e184 in check_dns_listeners (now=now@entry=1741871839) at
dnsmasq.c:1912
#3 0x000055555555dfc0 in main (argc=<optimized out>, argv=<optimized out>) at
dnsmasq.c:1289
(gdb) quit
Please consider the following patch...
Credits go to pedro0311 <pe...@freshtomato.org>
From 0d87b0ac8ed525ab1eb43b753145702eba0db197 Mon Sep 17 00:00:00 2001
From: Tijs Van Buggenhout <tijs.van.buggenh...@axsguard.com>
Date: Thu, 13 Mar 2025 14:42:10 +0100
Subject: [PATCH] Partially revert "Always save forwarded query locally."
This partially reverts commit 3b6df06fb8cb3652d2e7afd085fae3f416408013.
---
src/forward.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/src/forward.c b/src/forward.c
index 8207a7e..939a4dc 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -353,9 +353,7 @@ static void forward_query(int udpfd, union mysockaddr
*udpaddr,
ede = EDE_NOT_READY;
flags = 0;
}
-
- master = daemon->serverarray[first];
-
+
/* don't forward A or AAAA queries for simple names, except the empty
name */
if (!flags &&
option_bool(OPT_NODOTS_LOCAL) &&
@@ -368,6 +366,8 @@ static void forward_query(int udpfd, union mysockaddr
*udpaddr,
if (flags || ede == EDE_NOT_READY)
goto reply;
+ master = daemon->serverarray[first];
+
if (!(forward = get_new_frec(now, master, 0)))
goto reply;
/* table full - flags == 0, return REFUSED */
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