[Bug 596859] [NEW] ntp profile denies write access to serial devices

[Paul Crawford]

Public bug reported:

Binary package hint: ntp

While reporting and testing for bug #596010 using the 10.04 release
candidate I found that the intended user-tunable apparmor options in
/etc/apparmor.d/tunables/ntpd do not work correctly due to the settings
in /etc/apparmor.d/usr.sbin.ntpd including them with read-only
permission.

While it might initially seem reasonable that you just 'read' the time
from a serial port GPS or similar, in practice most of the drivers for
serial clocks also need write-access to configure and/or poll them for
the time.

I found that changing line 35 in  /etc/apparmor.d/usr.sbin.ntpd from:

  @{NTPD_DEVICE} r,

to this:

  @{NTPD_DEVICE} rw,

seems to fix things so allowing /dev/ttyS* in the tunables works OK.

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

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ntp profile denies write access to serial devices
https://bugs.launchpad.net/bugs/596859
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