[Bug 2043114] Re: sshd segmentation fault on 20.04.6 (focal)

[Ivaylo Markov]

Apologies for the multiple messages, but I was under the impression that
apport-collect would upload the actual core dump file here :)

** Attachment added: "sshd abort crash report"
   https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/2043114/+attachment/5717896/+files/_usr_sbin_sshd.0.crash

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https://bugs.launchpad.net/bugs/2043114

Title:
  sshd segmentation fault on 20.04.6 (focal)

Status in openssh package in Ubuntu:
  Confirmed

Bug description:
  We have a physical server running Ubuntu 20.04.6 LTS (amd64) and openssh-server 1:8.2p1-4ubuntu0.9. Sometimes sshd crashes with a segmentation fault on remote login with key authentication:
  [193107.651745] sshd[1229630]: segfault at 5557eba6a008 ip 00007f2326a2ca53 sp 00007ffcba40c510 error 4 in libc-2.31.so[7f23269b8000+178000]

  We’ve changed only the following values in the stock sshd_config file:

  LogLevel DEBUG
  PasswordAuthentication no
  MaxStartups 100:30:100

  The server is used for automated software testing, and sometimes our test suite might make a large amount of SSH connections in a short period of time, which seems to be correlated with the crashes. But at the same time, I have to note that the connection count was not near the MaxStartups limit, and we’ve had crashes before adding that setting.
  Since the backtrace shows the debug logging function in the stack, we’re currently experimenting with using `LogLevel INFO` to try and isolate the issue.

  I am attaching the backtrace. I could provide the full dump file,
  although I am hesitant due to the possibility of private keys or other
  sensitive information leaking.

  # apt-cache policy openssh-server
  openssh-server:
    Installed: 1:8.2p1-4ubuntu0.9
    Candidate: 1:8.2p1-4ubuntu0.9
    Version table:
   *** 1:8.2p1-4ubuntu0.9 500
          500 http://mirrors.storpool.com/ubuntu/archive focal-updates/main amd64 Packages
          500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages
          100 /var/lib/dpkg/status
       1:8.2p1-4 500
          500 http://mirrors.storpool.com/ubuntu/archive focal/main amd64 Packages
  --- 
  ProblemType: Bug
  ApportVersion: 2.20.11-0ubuntu27.27
  Architecture: amd64
  CasperMD5CheckResult: skip
  DistroRelease: Ubuntu 20.04
  Package: openssh-server 1:8.2p1-4ubuntu0.9
  PackageArchitecture: amd64
  ProcVersionSignature: Ubuntu 5.4.0-128.144-generic 5.4.210
  Tags:  focal
  Uname: Linux 5.4.0-128-generic x86_64
  UpgradeStatus: Upgraded to focal on 2021-01-13 (1030 days ago)
  UserGroups: N/A
  _MarkForUpload: True

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