Dear Simon, CC mailing list,
today I've received a report of latest dnsmasq embedded into Pi-hole
crashing when www.facebook.com is visited (but only when logged in). I
was able to reproduce this myself after creating a (fake) account.
The hit/miss ratio is not 100% but it should be possible to trigger the
crash within a couple of tries. I tried Google Chrome on Linux for
reproducing the crash (the report was Chrome on Windows). For this test,
I used only one upstream server: 8.8.8.8
A PCAP I recorded using dumpmask=0xFFFF is attached.
When the SIGSEGV happens, it can happen in a few different but related
code places, let me summarize the two location I found most often below:
https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob;f=src/blockdata.c;h=444a03a6798fce5da839f199df4a9326ab17188a;hb=HEAD#l217
Thread 1 "pihole-FTL" received signal SIGSEGV, Segmentation fault.
blockdata_retrieve (block=<optimized out>, len=13, data=0x556b98069ac0,
data@entry=0x0) at /app/FTL/src/dnsmasq/blockdata.c:217
217 memcpy(d, b->key, blen);
(gdb) where
#0 blockdata_retrieve (block=<optimized out>, len=13,
data=0x556b98069ac0, data@entry=0x0) at
/app/FTL/src/dnsmasq/blockdata.c:217
#1 0x0000556b95cd2092 in answer_request
(header=header@entry=0x556b9800e290, limit=limit@entry=0x556b9800e490
"", qlen=qlen@entry=31, local_addr=..., local_addr@entry=...,
local_netmask=...,
local_netmask@entry=..., now=now@entry=1693587354,
ad_reqd=<optimized out>, do_bit=<optimized out>,
have_pseudoheader=<optimized out>, stale=<optimized out>,
filtered=<optimized out>)
at /app/FTL/src/dnsmasq/rfc1035.c:2175
#2 0x0000556b95cac02d in receive_query
(listen=listen@entry=0x556b98002d60, now=now@entry=1693587354) at
/app/FTL/src/dnsmasq/forward.c:1921
#3 0x0000556b95c99b61 in check_dns_listeners (now=now@entry=1693587354)
at /app/FTL/src/dnsmasq/dnsmasq.c:1864
#4 0x0000556b95c9bd2d in main_dnsmasq (argc=<optimized out>,
argv=<optimized out>) at /app/FTL/src/dnsmasq/dnsmasq.c:1271
#5 0x0000556b95bfaf76 in main (argc=<optimized out>,
argv=0x7ffff6ee9598) at /app/FTL/src/main.c:152
sometimes the crash happens in
https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob;f=src/blockdata.c;h=444a03a6798fce5da839f199df4a9326ab17188a;hb=HEAD#l177
Thread 1 "pihole-FTL" received signal SIGSEGV, Segmentation fault.
blockdata_free (blocks=0x3368023268020600) at
/app/FTL/src/dnsmasq/blockdata.c:177
177 void blockdata_free(struct blockdata *blocks)
(gdb) where
#0 blockdata_free (blocks=0x3368023268020600) at
/app/FTL/src/dnsmasq/blockdata.c:177
#1 0x0000560c710c9715 in cache_scan_free
(name=name@entry=0x560c7272f6d0 "star.c10r.facebook.com",
addr=addr@entry=0x7ffe4bdaa9a0, class=class@entry=1,
now=now@entry=1693587879, flags=flags@entry=1082130440,
target_crec=target_crec@entry=0x7ffe4bdaa870,
target_uid=0x7ffe4bdaa86c) at /app/FTL/src/dnsmasq/cache.c:541
#2 0x0000560c710cd43e in really_insert (name=0x560c7272f6d0
"star.c10r.facebook.com", addr=0x7ffe4bdaa9a0, class=1, now=1693587879,
ttl=60, flags=1082130440) at /app/FTL/src/dnsmasq/cache.c:657
#3 0x0000560c7110aa6e in extract_addresses
(header=header@entry=0x560c7273f290, qlen=<optimized out>,
name=0x560c7272f6d0 "star.c10r.facebook.com", now=now@entry=1693587879,
ipsets=ipsets@entry=0x0,
nftsets=nftsets@entry=0x0, is_sign=0, check_rebind=0,
no_cache_dnssec=0, secure=0, doctored=0x7ffe4bdaaa9c) at
/app/FTL/src/dnsmasq/rfc1035.c:921
#4 0x0000560c710e39b6 in process_reply
(header=header@entry=0x560c7273f290, now=now@entry=1693587879,
server=0x560c7273d6d0, n=<optimized out>, n@entry=157, check_rebind=0,
no_cache=no_cache@entry=0,
cache_secure=0, bogusanswer=0, ad_reqd=0, do_bit=0,
added_pheader=128, query_source=0x560c7278e150, limit=0x560c7273f760 "",
ede=<optimized out>) at /app/FTL/src/dnsmasq/forward.c:833
#5 0x0000560c710e86c0 in return_reply (now=now@entry=1693587879,
forward=forward@entry=0x560c7278e150,
header=header@entry=0x560c7273f290, n=157, n@entry=140730171042832,
status=<optimized out>)
at /app/FTL/src/dnsmasq/forward.c:1397
#6 0x0000560c710e8c70 in dnssec_validate
(forward=forward@entry=0x560c7278e150,
header=header@entry=0x560c7273f290, plen=140730171042832,
status=<optimized out>, status@entry=524288, now=now@entry=1693587879)
at /app/FTL/src/dnsmasq/forward.c:1109
#7 0x0000560c710e8c1a in dnssec_validate
(forward=forward@entry=0x560c72731a70,
header=header@entry=0x560c7273f290, plen=plen@entry=855,
status=status@entry=524288, now=now@entry=1693587879)
at /app/FTL/src/dnsmasq/forward.c:1124
#8 0x0000560c710e9674 in reply_query (fd=<optimized out>,
now=now@entry=1693587879) at /app/FTL/src/dnsmasq/forward.c:1319
#9 0x0000560c710d5dff in check_dns_listeners (now=now@entry=1693587879)
at /app/FTL/src/dnsmasq/dnsmasq.c:1836
#10 0x0000560c710d7d2d in main_dnsmasq (argc=<optimized out>,
argv=<optimized out>) at /app/FTL/src/dnsmasq/dnsmasq.c:1271
#11 0x0000560c71036f76 in main (argc=<optimized out>,
argv=0x7ffe4bdab088) at /app/FTL/src/main.c:152
Best,
Dominik
