[Bug 1691763] Re: mdadm segfaults in lxd container

[lordaro]

I just encountered this myself. Was a bit bored, so did some testing.

mdadm master HEAD (4.0) does not segfault, nor does the HEAD of the
branch mdadm-3.3.4

However, if you acquire the actual version of source used by ubuntu
(3.3, from 2013(!)) and compile, and run through gdb, you get:

Program received signal SIGSEGV, Segmentation fault.
strlen () at ../sysdeps/x86_64/strlen.S:106
106     ../sysdeps/x86_64/strlen.S: No such file or directory.
(gdb) bt
#0  strlen () at ../sysdeps/x86_64/strlen.S:106
#1  0x00007ffff7a9847e in __GI___strdup (s=0x0) at strdup.c:41
#2  0x0000000000477ddf in xstrdup (str=0x0) at xmalloc.c:66
#3  0x0000000000435009 in add_new_arrays (mdstat=0x6b4480, statelist=0x7fffffffe020, test=0, info=0x7fffffffe070)
    at Monitor.c:670
#4  0x00000000004336e7 in Monitor (devlist=0x0, mailaddr=0x6b4510 "root", alert_cmd=0x0, c=0x7fffffffe210,
    daemonise=0, oneshot=1, dosyslog=0, pidfile=0x0, increments=20, share=0) at Monitor.c:223
#5  0x0000000000406cd1 in main (argc=4, argv=0x7fffffffe6d8) at mdadm.c:1448


Monitor.c:670 is

st->devname = xstrdup(get_md_name(mse->devnm));

with the obvious unchecked return value of get_md_name

Looking through the git history, this was fixed with
http://git.neil.brown.name/?p=mdadm.git;a=commitdiff;h=1e08717f0b7856b389e9d5eb2dc330d146636183

I'd recommend backporting this patch :)

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

Title:
  mdadm segfaults in lxd container

Status in mdadm package in Ubuntu:
  Confirmed

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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