Subject: rsyslog: segfaults with latest libc6 (2.42-4)

From: "Dimitris T." <[email-masked]>
Date: Thu, 04 Dec 2025 14:15:45 +0200

Package: rsyslog
Version: 8.2510.0-5devuan1
Severity: grave
Justification: renders package unusable

Hey,
since upgrading libc6 today, rsyslog fails with following message : 

# /usr/sbin/rsyslogd -n -iNONE
/usr/sbin/rsyslogd: Relink `/usr/lib/x86_64-linux-gnu/libfastjson.so.4' with `/usr/lib/x86_64-linux-gnu/libm.so.6' for IFUNC symbol `modf'
Segmentation fault

dmesg : 
rsyslogd[4291]: segfault at 9c ip 00007fb603e233a7 sp 00007ffe50362148 error 4 in libm.so.6[4b3a7,7fb603de9000+82000] likely on CPU 2 (core 0, socket 0)

after downgrading libc6, libc6-bin, locales to testing version (2.41-12) , rsyslog works again as it should.

thanks,
d.

-- System Information:
Distributor ID:	Devuan
Description:	Devuan GNU/Linux 7 (freia/ceres)
Release:	7
Codename:	freia ceres
Architecture: x86_64

Kernel: Linux 6.17.9+deb14-amd64 (SMP w/4 CPU threads; PREEMPT)
Locale: LANG=el_GR.UTF-8, LC_CTYPE=el_GR.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: runit (via /run/runit.stopit)
LSM: AppArmor: enabled

Versions of packages rsyslog depends on:
ii  init-system-helpers        1.69devuan1
ii  libc6                      2.42-4
ii  libestr0                   0.1.11-2
ii  libfastjson4               1.2304.0-2
ii  liblognorm5                2.0.7-1
ii  libuuid1                   2.41.2-4devuan1
ii  libzstd1                   1.5.7+dfsg-2
ii  lsb-base                   11.6
ii  sysvinit-utils [lsb-base]  3.15-6devuan1
ii  zlib1g                     1:1.3.dfsg+really1.3.1-1+b1

Versions of packages rsyslog recommends:
ii  logrotate  3.22.0-1

Versions of packages rsyslog suggests:
pn  rsyslog-clickhouse                <none>
pn  rsyslog-doc                       <none>
pn  rsyslog-docker                    <none>
pn  rsyslog-elasticsearch             <none>
pn  rsyslog-gssapi                    <none>
pn  rsyslog-hiredis                   <none>
pn  rsyslog-kafka                     <none>
pn  rsyslog-kubernetes                <none>
pn  rsyslog-mongodb                   <none>
pn  rsyslog-mysql                     <none>
pn  rsyslog-openssl | rsyslog-gnutls  <none>
pn  rsyslog-pgsql                     <none>
pn  rsyslog-relp                      <none>
pn  rsyslog-snmp                      <none>

-- Configuration Files:
/etc/logrotate.d/rsyslog [file not found]

-- no debconf information

---

From: "Dimitris T." <[email-masked]>
Date: Thu, 4 Dec 2025 14:39:56 +0200

hadn't checked older bugs...,

seems to be the same(?)/similar to 
https://bugs.devuan.org/cgi/bugreport.cgi?bug=908

thanks,

d.

---

From: Mark Hindley <[email-masked]>
Date: Thu, 4 Dec 2025 13:44:01 +0000

Dimitris

Thanks.

> /usr/sbin/rsyslogd: Relink `/usr/lib/x86_64-linux-gnu/libfastjson.so.4' with `/usr/lib/x86_64-linux-gnu/libm.so.6' for IFUNC symbol `modf'

I have to admit to not understanding fully the intricacies of the linking and
symbols here.

There is an apparently equivalent Gentoo bug[1] that suggests this should be
resolved in libfastjson4. In other words it is for Debian to resolve.

Let me do some more research.

Mark

[1]  https://bugs.gentoo.org/961289

---

From: Mark Hindley <[email-masked]>
Date: Thu, 4 Dec 2025 13:45:17 +0000

> https://bugs.devuan.org/cgi/bugreport.cgi?bug=908

Yes, maybe my assessment there was incorrect. But the #908 OP didn't say it
wasn't fixed as I thought...

Mark

---

From: Mark Hindley <[email-masked]>
Date: Thu, 4 Dec 2025 17:43:27 +0000

Control: reassign -1 libfastjson-dev
Control: retitle -1 libfastjson4 linked without -lm causes segfault in rsyslog with libc6 2.42
Control: tags -1 debian
Control: affects -1 rsyslog
Control: forwarded -1 https://bugs.debian.org/1114612

Dimitris,

The issue appears to be lack of -lm linkage after a change in libc6 modf()
implementation in 2.42. However, it is only triggered in rsyslog builds without
systemd (hence only reports from  Devuan, Gentoo and Artix.)

It is fixed in libfastjson upstream[1]. Src:libfastjson is not forked in Devuan
and I have reopened the existing Debian bug[2] to request the fix be cherry-picked.

Mark

[1]  https://github.com/rsyslog/libfastjson/pull/167

[2]  https://bugs.debian.org/1114612