isc-dhcp-server AppArmor Denied on /proc/sys/net/ipv4/ip_local_port_range

[Steve Matos]

The following AppArmor denial errors are shown on startup:

Oct 25 00:52:00 xxx kernel: [ 556.231990] audit: type=1400 audit(1603601520.710:32): apparmor="DENIED" operation="open" profile="/usr/sbin/dhcpd" name="/proc/sys/net/ipv4/ip_local_port_range" pid=1982 comm="dhcpd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
Oct 25 00:52:00 xxx kernel: [ 556.232257] audit: type=1400 audit(1603601520.710:33): apparmor="DENIED" operation="open" profile="/usr/sbin/dhcpd" name="/proc/sys/net/ipv4/ip_local_port_range" pid=1982 comm="dhcpd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0

Fix is to edit /etc/apparmor.d/local/usr.sbin.dhcpd to have:
@{PROC}/sys/net/ipv4/ip_local_port_range r,

'lsb_release -rd':
Description: Ubuntu 20.04.1 LTS
Release: 20.04

isc-dhcp-server:
  Installed: 4.4.1-2.1ubuntu5
  Candidate: 4.4.1-2.1ubuntu5
  Version table:
 *** 4.4.1-2.1ubuntu5 500
        500 http://us.archive.ubuntu.com/ubuntu focal/main amd64 Packages
        100 /var/lib/dpkg/status

apparmor:
  Installed: 2.13.3-7ubuntu5.1
  Candidate: 2.13.3-7ubuntu5.1
  Version table:
 *** 2.13.3-7ubuntu5.1 500
        500 http://us.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     2.13.3-7ubuntu5 500
        500 http://us.archive.ubuntu.com/ubuntu focal/main amd64 Packages

[Michael Albert (albertmichaelj)]

I can confirm that I am seeing this same behavior. The proposed fix also worked for me.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Norman Henderson (norm-audrey)]

Proposed fix does not work for me, gives AppArmor parser error at line 3: Found unexpected character '''

I am also puzzled that this apparmor profile is completely different in form than others proposed e.g. at:
https://github.com/Harvie/AppArmor-Profiles/blob/master/usr.sbin.dhcpd
???

[Norman Henderson (norm-audrey)]

Admitting I know very little about apparmor, here is the profile that worked for me:
# cat /etc/apparmor.d/usr.sbin.dhcpd

# vim:syntax=apparmor

#include <tunables/global>

/usr/sbin/dhcpd {
  #include <abstractions/base>
  #include <abstractions/nameservice>

  capability chown,
  capability dac_override,
  capability net_bind_service,
  capability net_raw,
  capability setgid,
  capability setuid,
  capability sys_chroot,

  network inet raw,
  network packet raw,

  /etc/dhcp/dhcpd.conf r,
  /etc/dhcp/dhcpd6.conf r,
  /etc/bind/* r,
  /etc/hosts.allow r,
  /etc/hosts.deny r,
  @{PROC}/net/dev r,
  /usr/sbin/dhcpd rmix,
  /var/lib/dhcp/dhcpd.leases* rwl,
  /var/lib/dhcp/dhcpd6.leases* rwl,
  /{,var/}run/dhcp-server/dhcpd.pid wl,
}

[John Johansen (jjohansen)]

@norm-audrey as I read it the proposed fix does not contain a ''' character. It is the single line

  @{PROC}/sys/net/ipv4/ip_local_port_range r,

do you perhaps also copy the following line?

  'lsb_release -rd':

That would indeed result in the reported error. I am not sure how the profile in comment #4 would fix the originally reported deny message except by causing dhcpd to not use the code path resulting in the denial.

As for the difference between the two profiles. They don't have a completely different form, both have evolved from a similar base so they have much in common but do have some differences. The profile from https://github.com/Harvie/AppArmor-Profiles/blob/master/usr.sbin.dhcpd is an older version of the one carried by the upstream project https://gitlab.com/apparmor/apparmor/-/blob/master/profiles/apparmor/profiles/extras/usr.sbin.dhcpd.

Beyond whitespace differences I see

different conf file locations

  /etc/dhcpd.conf r,
  /etc/named.d/* r,

vs.

  /etc/dhcp/dhcpd.conf r,
  /etc/dhcp/dhcpd6.conf r,
  /etc/bind/* r,

broader lease location in the old upstream version

  /var/lib/dhcp/{db/,}dhcpd.leases* rwl,

vs.

  /var/lib/dhcp/dhcpd6.leases* rwl,

support for ipv6 leases in your version

  /var/lib/dhcp/{db/,}dhcpd.leases* rwl,

vs

  /var/lib/dhcp/dhcpd.leases* rwl,
  /var/lib/dhcp/dhcpd6.leases* rwl,

note: current upstream has broader leases and ipv6

  /var/lib/dhcp/{db/,}dhcpd{6,}.leases* rwl,

different pid file location

  /{,var/}run/dhcpd.pid wl

vs.

  /{,var/}run/dhcp-server/dhcpd.pid wl,

Some of this could come down to system configuration of dhcpd.

[Jesper Jensen (dkjkj)]

Confirm this is still a problem in
Description: Ubuntu 22.04.1 LTS
Release: 22.04

Solution proposed worked for me on a stock Ubuntu install