[Bug 1918410] Re: isc-dhcp-client denied by apparmor

[Sean Ford]

I have been doing Xenial -> Bionic -> Focal release upgrades and started
running into this apparmor issue with dhclient after reaching Focal.

I don't know the root issue, and it doesn't appear to impact
functionality (at least as far as I can tell on my hosts). However, I am
currently dealing with this by adding the following to
/etc/apparmor.d/local/sbin.dhclient:

    @{PROC}/[0-9]*/task/[0-9]*/comm rw,

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https://bugs.launchpad.net/bugs/1918410

Title:
  isc-dhcp-client denied by apparmor

Status in isc-dhcp package in Ubuntu:
  Confirmed

Bug description:
  Hi, I get weird errors in the audit log, seeing dhclient is being
  denied reading its comm or the comm of one of its tasks:

  
  [1383307.827378] audit: type=1400 audit(1615367094.054:162): apparmor="DENIED" operation="open" profile="/{,usr/}sbin/dhclient" name="/proc/1095210/task/1095213/comm" pid=1095210 comm="dhclient" requested_mask="wr" denied_mask="wr" fsuid=0 ouid=0

  This might or might not be linked with the fact that I can't get an
  IPv4 on this interface. Note that it happened to other, see this
  comment:

  https://bugs.launchpad.net/ubuntu/+source/apparmor/+bug/1413232/comments/8

  Or even an article recommending disabling apparmor for dhclient(!):
  https://blog.anthony-jacob.com/perte-dip-v4-sous-ubuntu-20-04-apparmor-et-dhclient/

  
  As I said, I'm not sure this is the root cause of the lack of IPv4 renewal, because running it manually *does* succeed in getting an IP. And running it in strace shows the EACCES failure:

  [pid 1095210] openat(AT_FDCWD, "/proc/self/task/1095211/comm", O_RDWRstrace: Process 1095211 attached
  ) = -1 EACCES (Permission non accordée)

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