[Bug 1481388] Re: NTP : Use-after-free in routing socket code after dropping root
Sebastien Bacher
seb128 at ubuntu.com
Tue Nov 10 16:52:41 UTC 2015
sponsored to precise/trusty/vivid (though i'm unsure vivid is useful
since it's not the current stable)
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https://bugs.launchpad.net/bugs/1481388
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:
In Progress
Status in ntp source package in Trusty:
In Progress
Status in ntp source package in Vivid:
In Progress
Status in ntp source package in Wily:
Fix Released
Status in ntp package in Debian:
Fix Released
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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