[Bug 1690485] Re: openssh-server SIGSYS with 'UsePrivilegeSeparation sandbox'
Seth Arnold
1690485 at bugs.launchpad.net
Thu Oct 26 22:44:40 UTC 2017
Hello Kevin, I don't want to step on Colin's toes here, but I couldn't
sort out anything from the logs or files so far. I've had success before
with perf to grab call graph information. The usual process is along the
lines of:
- enable the ddebs.ubuntu.com repository to get access to debug symbols:
https://wiki.ubuntu.com/Debug%20Symbol%20Packages
- install packages openssh-server-dbgsym libc6-dbgsym .. as needed
- Record perf results during testing with something like:
sudo perf record -e syscalls:sys_enter_socket -R -a --call-graph dwarf sleep 20
- test
- Check results with something like:
sudo perf script
With luck this will spit out the function names of the call chain at the time of the socket() syscall that is being killed (probably alongside a lot of unrelated instances -- it's possible to tune the perf line to narrow it down if necessary).
I hope this helps,
Thanks
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https://bugs.launchpad.net/bugs/1690485
Title:
openssh-server SIGSYS with 'UsePrivilegeSeparation sandbox'
Status in openssh package in Ubuntu:
New
Bug description:
The 'sshd' process gets 'authentication failure' and refuses to allow
any login.
dmesg indicates that the problem is SIGSYS on a call to 'socket'
(syscall #41, signal #31).
On a hunch, I decided to test whether the problem is related to
'seccomp' and changed /etc/ssh/sshd_config from the default
# UsePrivilegeSeparation sandbox
to the former standard value
UsePrivilegeSeparation yes
and logins started to work again.
Obviously, I'd like to have the additional protection that sandboxing
would give me.
ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: openssh-server 1:7.4p1-10
ProcVersionSignature: Ubuntu 4.10.0-20.22-generic 4.10.8
Uname: Linux 4.10.0-20-generic x86_64
ApportVersion: 2.20.4-0ubuntu4
Architecture: amd64
CurrentDesktop: XFCE
Date: Fri May 12 21:06:20 2017
InstallationDate: Installed on 2017-04-08 (35 days ago)
InstallationMedia:
SourcePackage: openssh
UpgradeStatus: Upgraded to zesty on 2017-04-24 (19 days ago)
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