[Bug 1481388] Re: NTP : Use-after-free in routing socket code after dropping root

[Chris J Arges]

Hello Eric, or anyone else affected,

Accepted ntp into trusty-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/ntp/1:4.2.6.p5+dfsg-
3ubuntu2.14.04.4 in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to
enable and use -proposed.  Your feedback will aid us getting this update
out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, and change the tag
from verification-needed to verification-done. If it does not fix the
bug for you, please add a comment stating that, and change the tag to
verification-failed.  In either case, details of your testing will help
us make a better decision.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance!

** Changed in: ntp (Ubuntu Trusty)
       Status: In Progress => Fix Committed

** Tags added: verification-needed

** Changed in: ntp (Ubuntu Precise)
       Status: In Progress => Fix Committed

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Title:
  NTP : Use-after-free in routing socket code after dropping root

Status in NTP:
  Fix Released
Status in ntp package in Ubuntu:
  Fix Released
Status in ntp source package in Precise:
  Fix Committed
Status in ntp source package in Trusty:
  Fix Committed
Status in ntp source package in Vivid:
  Fix Committed
Status in ntp source package in Wily:
  Fix Released
Status in ntp package in Debian:
  Unknown

Bug description:
  [Impact]

   * User experienced repeated segfaults at the same instruction pointer

  i/o error on routing socket No buffer space available - disabling
  segfault at 31 ip 0000000000000031 sp 00007ffff9f11788 error 14 in libpthread-2.15.so[7f967a5d9000+18000] 

  The remove_ and delete_ functions remove the current element from the
  asyncio_reader_list, and free it, respectively.

  We then return back to the loop at the top, wherein the asyncio_reader variable still points at the now-freed element, whose contents are (in theory) now scrambled
  by having link pointers, etc, from internal malloc state overlaying the data.

  [Test Case]

  You can easily reproduce the bug by :

  - Lowering the sysctl value net.core.rmem_max

  $ sysctl -w net.core.wmem_max=<LOWER_VALUE>
  This sets the max OS send buffer size for all types of connections.

  - Adding multiple network interfaces and static routes.

  [Regression Potential]

  None expected since the fix is already available upstream
  (https://github.com/ntp-project/ntp.git) and Debian package.

  If after installing the patch, user are receiving this kind of message in /var/log/syslog : "routing socket reports: No buffer space available".
  The next step, would be to increase the "net.core.rmem_max" and "net.core.wmem_max" values equally until the "routing socket reports: No buffer space available" message no longer showed up.

  [Other Info]

  NTP upstream (https://github.com/ntp-project/ntp.git)
  [Bug 2224] Use-after-free in routing socket code after dropping root. - Commit: d6df9d3
  [Bug 2890] Ignore ENOBUFS on routing netlink socket. - Commit: db47bd4 

  The use-after-free bug has been fix in Debian release (closes: #795315)
  Will submit the ignore-ENOBUFS-on-routing-netlink-socket in Debian in the next days.

  [Original Description]

  We have 1 server (among hundreds) that its ntp service is crashing.

  A few minute/seconds after a start attempts we can see the following in syslog:
  ntpd[2729]: peers refreshed
  ntpd[2729]: Listening on routing socket on fd #49 for interface updates
  ntpd[2729]: i/o error on routing socket No buffer space available - disabling
  kernel: [157516.495224] ntpd[2729]: segfault at 31 ip 0000000000000031 sp 00007ffff9f11788 error 14 in libpthread-2.15.so[7f967a5d9000+18000]

  OS: Ubuntu 12.04.4 LTS
  Kernel: 3.11.0-19-generic

  I tried to compare it to other servers, and the only thing I could find that is different is that while it's up (before it crashes) I can see the following when running "lsof | grep ntp":
  ntpd 2729 ntp 49u sock 0,7 0t0 2473952565 can't identify protocol.

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