[Bug 1691763] [NEW] mdadm segfaults in lxd container

[Brian Candler]

Public bug reported:

Inside a 16.04 lxd container (running in default unprivileged mode),
inside a 16.04 host:

# /etc/cron.daily/mdadm
Segmentation fault (core dumped)

# strace -f /sbin/mdadm --monitor --scan --oneshot
...
brk(0x1ba1000)                          = 0x1ba1000
mknod("/dev/.tmp.md1", S_IFBLK|0600, makedev(9, 1)) = -1 EPERM (Operation not permitted)
--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0} ---
+++ killed by SIGSEGV (core dumped) +++
Segmentation fault (core dumped)

This is troublesome because (a) mdadm is installed by default, (b) mdadm
runs under a daily cron job, (c) cron sends out errors via E-mail.  So
you get spammed from each container.

As others have observed[^1], the workaround is to remove mdadm from
inside lxd containers.

[^1] https://blog.sleeplessbeastie.eu/2017/05/04/how-to-fix-mdadm-
segfault-inside-lxc-container/

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: mdadm 3.3-2ubuntu7.2
ProcVersionSignature: Ubuntu 4.8.0-52.55~16.04.1-generic 4.8.17
Uname: Linux 4.8.0-52-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
Date: Thu May 18 13:48:22 2017
Lsusb:
 Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
 Bus 001 Device 002: ID 413c:a001 Dell Computer Corp. Hub
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: Dell Inc. PowerEdge R230
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.8.0-52-generic root=/dev/mapper/ix--mon2-root ro console=tty1 console=ttyS0,115200
SourcePackage: mdadm
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 01/12/2017
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 2.0.8
dmi.board.name: 0DWX9P
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 23
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr2.0.8:bd01/12/2017:svnDellInc.:pnPowerEdgeR230:pvr:rvnDellInc.:rn0DWX9P:rvrA00:cvnDellInc.:ct23:cvr:
dmi.product.name: PowerEdge R230
dmi.sys.vendor: Dell Inc.
etc.blkid.tab: Error: [Errno 2] No such file or directory: '/etc/blkid.tab'
initrd.files: Error: [Errno 2] No such file or directory: '/boot/initrd.img-4.8.0-52-generic'

** Affects: mdadm (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug uec-images xenial

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https://bugs.launchpad.net/bugs/1691763

Title:
  mdadm segfaults in lxd container

Status in mdadm package in Ubuntu:
  New

Bug description:
  Inside a 16.04 lxd container (running in default unprivileged mode),
  inside a 16.04 host:

  # /etc/cron.daily/mdadm
  Segmentation fault (core dumped)

  # strace -f /sbin/mdadm --monitor --scan --oneshot
  ...
  brk(0x1ba1000)                          = 0x1ba1000
  mknod("/dev/.tmp.md1", S_IFBLK|0600, makedev(9, 1)) = -1 EPERM (Operation not permitted)
  --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0} ---
  +++ killed by SIGSEGV (core dumped) +++
  Segmentation fault (core dumped)

  This is troublesome because (a) mdadm is installed by default, (b)
  mdadm runs under a daily cron job, (c) cron sends out errors via
  E-mail.  So you get spammed from each container.

  As others have observed[^1], the workaround is to remove mdadm from
  inside lxd containers.

  [^1] https://blog.sleeplessbeastie.eu/2017/05/04/how-to-fix-mdadm-
  segfault-inside-lxc-container/

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: mdadm 3.3-2ubuntu7.2
  ProcVersionSignature: Ubuntu 4.8.0-52.55~16.04.1-generic 4.8.17
  Uname: Linux 4.8.0-52-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.5
  Architecture: amd64
  Date: Thu May 18 13:48:22 2017
  Lsusb:
   Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
   Bus 001 Device 002: ID 413c:a001 Dell Computer Corp. Hub
   Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
  MachineType: Dell Inc. PowerEdge R230
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.8.0-52-generic root=/dev/mapper/ix--mon2-root ro console=tty1 console=ttyS0,115200
  SourcePackage: mdadm
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 01/12/2017
  dmi.bios.vendor: Dell Inc.
  dmi.bios.version: 2.0.8
  dmi.board.name: 0DWX9P
  dmi.board.vendor: Dell Inc.
  dmi.board.version: A00
  dmi.chassis.type: 23
  dmi.chassis.vendor: Dell Inc.
  dmi.modalias: dmi:bvnDellInc.:bvr2.0.8:bd01/12/2017:svnDellInc.:pnPowerEdgeR230:pvr:rvnDellInc.:rn0DWX9P:rvrA00:cvnDellInc.:ct23:cvr:
  dmi.product.name: PowerEdge R230
  dmi.sys.vendor: Dell Inc.
  etc.blkid.tab: Error: [Errno 2] No such file or directory: '/etc/blkid.tab'
  initrd.files: Error: [Errno 2] No such file or directory: '/boot/initrd.img-4.8.0-52-generic'

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