On 15/10/2021 04:45, Eloy Paris wrote: > Hi Simon, > > I am running 2.87test4, which has the commit you mention below. > > I've tested bringing down and up the external interfaces of the machine > (the ones that dnsmasq uses to reach the recursive DNS servers to > fulfill DNS requests it receives) and have not been able to reproduce a > crash anymore. > > However, after bringing down an interface and a few seconds later > bringing it back up, DNS resolution stops working. > > I see this in the system log right after I re-enable the interface that > I previously disabled: > > Oct 14 23:28:14 chapilu dnsmasq[79367]: reading /etc/resolv.conf > > and the packet capture shows: > > 23:29:24.737039 IP 192.168.122.165.60261 > 192.168.122.1.53: 18552+ A? > google.com. (28) > 23:29:24.737126 IP 192.168.122.1.53 > 192.168.122.165.60261: 18552 Refused > 0/0/0 (28) > > Under what conditions does dnsmasq respond to a resolution request with > REFUSED; no servers in /etc/resolv.conf? > > I guess there might be a race condition here because I just sent SIGHUP > to the dnsmasq process and the system log shows this: >
As Petr says, the REFUSED reply is when there are no suitable servers to forward a query to. Based on the previous crash, which is triggered by there being no configured servers, this is expected. Reading /etc/resolv.conf is inherently racy - but the code should keep trying in the case that it finds an empty /etc/resolv.conf to mitigate this. You're not setting --no-poll are you? Simon. > Oct 14 23:38:34 chapilu dnsmasq[79367]: read /etc/hosts - 4 addresses > > and now DNS resolution works again! > > No idea why dnsmasq is automatically detecting one change in > /etc/resolv.conf, and it apparently is one that does not contain any > servers. > > Cheers, > > Eloy Paris.- > > On Wed, Oct 13, 2021 at 09:44:56AM +0100, Simon Kelley wrote: > >> Based on the location of the crash, and the circumstances that cause it, >> my guess is that this will be fixed by >> >> https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=d290630d31f4517ab26392d00753d1397f9a4114 >> >> Please could you try that, and get back to us if it doesn't sort the >> problem? >> >> >> Cheers, >> >> Simon. >> >> >> On 13/10/2021 05:03, Eloy Paris wrote: >>> Sorry, I forgot the backtrace; here it is: >>> >>> (gdb) bt >>> #0 0x0000561772564d46 in lookup_domain (domain=0x561772b1d7a0 >>> "enterprise.activity.windows.com", flags=flags@entry=128, >>> lowout=lowout@entry=0x7ffe8a4b63ac, >>> highout=highout@entry=0x7ffe8a4b63b0) at domain-match.c:234 >>> #1 0x0000561772532b1e in forward_query (udpfd=5, >>> udpaddr=udpaddr@entry=0x7ffe8a4b6500, >>> dst_addr=dst_addr@entry=0x7ffe8a4b64e0, >>> dst_iface=dst_iface@entry=13, header=header@entry=0x561772b1fae0, >>> plen=plen@entry=49, limit=0x561772b1fce0 "", now=1634091453, >>> forward=0x0, ad_reqd=0, do_bit=0) at forward.c:258 >>> #2 0x000056177253387e in receive_query >>> (listen=listen@entry=0x561772b1f400, now=now@entry=1634091453) at >>> forward.c:1636 >>> #3 0x0000561772538b7c in check_dns_listeners (now=now@entry=1634091453) at >>> dnsmasq.c:1810 >>> #4 0x000056177251888b in main (argc=<optimized out>, argv=<optimized out>) >>> at dnsmasq.c:1237 >>> (gdb) >>> >>> >>> On Tue, Oct 12, 2021 at 10:55:22PM -0400, Eloy Paris wrote: >>>> Hello, >>>> >>>> I am experiencing crashes in dnsmasq (2.86). I am able to reproduce it >>>> though I am not sure about the exact sequence of events -- it happens >>>> when I enable/disable my Ethernet NIC and disable/enable my wireless >>>> NIC. >>>> >>>> In this use case, dnsmasq provides DNS and DHCP for a virtual machine >>>> (VM) running on KVM. Something like this: >>>> >>>> +-- (Ethernet)-+ >>>> | | >>>> Internet + Hypervisor (virbr0) --- VM >>>> | | >>>> +--- (Wi-fi)---+ >>>> >>>> The interfaces I am enabling and disabling are on the hypervisor >>>> ("Ethernet" and "Wi-fi" above; virbr0 never goes down). >>>> >>>> I guess dnsmasq does not handle gracefully receiving a DNS request from >>>> the VM when the external interfaces of the hypervisor (Ethernet or >>>> wi-fi) go down? >>>> >>>> Some details below; happy to provide more information if that's not >>>> enough to get to the bottom of it. >>>> >>>> Cheers, >>>> >>>> Eloy Paris.- >>>> >>>> ---------------------------------------------------------------------- >>>> >>>> elparis@chapilu[0]:~$ sudo coredumpctl debug dnsmasq >>>> [sudo] Mot de passe de elparis : >>>> PID: 46002 (dnsmasq) >>>> UID: 65534 (nobody) >>>> GID: 65534 (nobody) >>>> Signal: 11 (SEGV) >>>> Timestamp: Tue 2021-10-12 22:17:33 EDT (11min ago) >>>> Command Line: /usr/bin/dnsmasq >>>> --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro >>>> --dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper >>>> Executable: /usr/bin/dnsmasq >>>> Control Group: /system.slice/libvirtd.service >>>> Unit: libvirtd.service >>>> Slice: system.slice >>>> Boot ID: a42fe0fbd18649ad8a6951687e2855d8 >>>> Machine ID: 3d34409507634591951da9abb51a3942 >>>> Hostname: chapilu >>>> Storage: >>>> /var/lib/systemd/coredump/core.dnsmasq.65534.a42fe0fbd18649ad8a6951687e2855d8.46002.1634091453000000.zst >>>> (present) >>>> Disk Size: 204.6K >>>> Message: Process 46002 (dnsmasq) of user 65534 dumped core. >>>> >>>> Found module linux-vdso.so.1 with build-id: >>>> c6d7bcf242640b81aef03f231535fa4c2486c744 >>>> Found module libffi.so.7 with build-id: >>>> de60e99f39569d11d09160bbdcd486cedc87d2b6 >>>> Found module libp11-kit.so.0 with build-id: >>>> 5314ec746546ada6f442b6fdfae15eab9f6d3cdc >>>> Found module libcrypto.so.1.1 with build-id: >>>> 6d23f0a3f354825868d044684fad31d482cc9210 >>>> Found module libdl.so.2 with build-id: >>>> 5abc547e7b0949f89f3c0e21ab0c8331a7440a8a >>>> Found module libcrypt.so.2 with build-id: >>>> 3743451bdaf36f951f926927633fd964813025d0 >>>> Found module libnss_systemd.so.2 with build-id: >>>> 22990ff716d182c427e26b7a3cf94048b55b3e75 >>>> Found module libnss_files.so.2 with build-id: >>>> 1a36dfc01d3a1010b2ee79766a24a8090a3266d5 >>>> Found module libgpg-error.so.0 with build-id: >>>> ba85170c2d9343ea05eea8fa2048c212ff4ef552 >>>> Found module libgcrypt.so.20 with build-id: >>>> db45f5d5e0f7af1e77324fea1885f974619ad268 >>>> Found module libcap.so.2 with build-id: >>>> c1674f9082fedd415876b9f7d9712269163259b5 >>>> Found module liblz4.so.1 with build-id: >>>> e63600ab23b2f6997f42fac2fa56e1f02ce159a1 >>>> Found module libzstd.so.1 with build-id: >>>> 4b10444c1560ebc574af4d5f488b7408b22d450e >>>> Found module liblzma.so.5 with build-id: >>>> 8b615460aa230708c5183f16bede67aa0437d95e >>>> Found module librt.so.1 with build-id: >>>> 75484da2d6f1515189eefa076e0a40328834cd16 >>>> Found module ld-linux-x86-64.so.2 with build-id: >>>> 040cc3dd10461562f177df39e3be2f3704258c3c >>>> Found module libmnl.so.0 with build-id: >>>> fdf3a318247060fa3e451d511ebaf23a7396d1dd >>>> Found module libnfnetlink.so.0 with build-id: >>>> 273cc877c7b2ff41e88753edda777d7f1c4017ca >>>> Found module libunistring.so.2 with build-id: >>>> 015ac6d6bcb60b7d8bea31a80d1941b06e8636ab >>>> Found module libsystemd.so.0 with build-id: >>>> f776aaa16b4e2ba7056d01d928e4b2726ffe2b8b >>>> Found module libpthread.so.0 with build-id: >>>> 07c8f95b4f3251d08550217ad8a1f31066229996 >>>> Found module libc.so.6 with build-id: >>>> 4b406737057708c0e4c642345a703c47a61c73dc >>>> Found module libgmp.so.10 with build-id: >>>> e58d34ab389d1b649c24195c2d145e3ff2e58290 >>>> Found module libhogweed.so.6 with build-id: >>>> 2d70cff7b1841b4d9ca4e8e7726cd4b944c07fdc >>>> Found module libnettle.so.8 with build-id: >>>> 9a878e513c02007598fcf1e2e286c2203f13536e >>>> Found module libnetfilter_conntrack.so.3 with build-id: >>>> 0ad526380b1a1986a1e471a84d88d5f2a7fedd80 >>>> Found module libidn2.so.0 with build-id: >>>> 1ce2b50ad9f9821c2c629b521cf5a3c99593d332 >>>> Found module libdbus-1.so.3 with build-id: >>>> 74f2ab9c60512f3a93c932c3f627564d42e0b11e >>>> Found module dnsmasq with build-id: >>>> 17b49d0999133997748526c51d99bf8b932fb79d >>>> Stack trace of thread 46002: >>>> #0 0x0000561772564d46 lookup_domain (dnsmasq + 0x55d46) >>>> #1 0x0000561772532b1e forward_query (dnsmasq + 0x23b1e) >>>> #2 0x000056177253387e receive_query (dnsmasq + 0x2487e) >>>> #3 0x0000561772538b7c check_dns_listeners (dnsmasq + >>>> 0x29b7c) >>>> #4 0x000056177251888b main (dnsmasq + 0x988b) >>>> #5 0x00007f85147e4b25 __libc_start_main (libc.so.6 + >>>> 0x27b25) >>>> #6 0x00005617725197ae _start (dnsmasq + 0xa7ae) >>>> >>>> GNU gdb (GDB) 11.1 >>>> Copyright (C) 2021 Free Software Foundation, Inc. >>>> License GPLv3+: GNU GPL version 3 or later >>>> <http://gnu.org/licenses/gpl.html> >>>> This is free software: you are free to change and redistribute it. >>>> There is NO WARRANTY, to the extent permitted by law. >>>> Type "show copying" and "show warranty" for details. >>>> This GDB was configured as "x86_64-pc-linux-gnu". >>>> Type "show configuration" for configuration details. >>>> For bug reporting instructions, please see: >>>> <https://www.gnu.org/software/gdb/bugs/>. >>>> Find the GDB manual and other documentation resources online at: >>>> <http://www.gnu.org/software/gdb/documentation/>. >>>> >>>> For help, type "help". >>>> Type "apropos word" to search for commands related to "word"... >>>> Reading symbols from /usr/bin/dnsmasq... >>>> [New LWP 46002] >>>> [Thread debugging using libthread_db enabled] >>>> Using host libthread_db library "/usr/lib/libthread_db.so.1". >>>> Core was generated by `/usr/bin/dnsmasq >>>> --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-'. >>>> Program terminated with signal SIGSEGV, Segmentation fault. >>>> #0 0x0000561772564d46 in lookup_domain (domain=0x561772b1d7a0 >>>> "enterprise.activity.windows.com", flags=flags@entry=128, >>>> lowout=lowout@entry=0x7ffe8a4b63ac, >>>> highout=highout@entry=0x7ffe8a4b63b0) at domain-match.c:234 >>>> 234 domain-match.c: Aucun fichier ou dossier de ce type. >>>> (gdb) >>>> > _______________________________________________ Dnsmasq-discuss mailing list Dnsmasq-discuss@lists.thekelleys.org.uk https://lists.thekelleys.org.uk/cgi-bin/mailman/listinfo/dnsmasq-discuss
