[Bug 857524] [NEW] dhclient-script will not work with read-only /etc

[Scott Moser]

Public bug reported:

dhclient-script attempts to support read-only root , but it wont correctly work.
For a read-only root to work, and support dhclient-script writing to /etc/resolv.conf, then /etc/resolv.conf would have to be a symlink to a writeable location (ie, /run).

To that end, dhclient-script attempts to check and see if / is going to
be mounted 'rw' and only wait for that case if it is.

The problem is that it basically has the following logic:
  if root_will_be_mounted_rw; then
      wait-for-writable /etc/
  fi
  new_resolv_conf=/etc/resolv.conf.dhclient-new
  write new file to to $new_resolv_conf
  change attributes of $new_resolv_conf to match resolv.conf
  mv $new_resolv_conf /etc/resolv.conf

That doesn't work if /etc is read-only and /etc/resolv.conf is a symlink for the following reasons:
 * $new_resolv_conf is being written to /etc/ (and wont be writable)
 * the mv will actually break the symlink and try to create a new file in /etc

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: isc-dhcp-client 4.1.1-P1-17ubuntu9
ProcVersionSignature: Ubuntu 3.0.0-11.18-generic 3.0.4
Uname: Linux 3.0.0-11-generic x86_64
ApportVersion: 1.23-0ubuntu1
Architecture: amd64
Date: Fri Sep 23 11:50:56 2011
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 10.04 "Lucid Lynx" - Beta amd64 (20100318)
ProcEnviron:
 SHELL=/bin/bash
 PATH=(custom, user)
 LANG=en_US.UTF-8
SourcePackage: isc-dhcp
UpgradeStatus: Upgraded to oneiric on 2010-11-15 (311 days ago)

** Affects: isc-dhcp (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug oneiric running-unity

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https://bugs.launchpad.net/bugs/857524

Title:
  dhclient-script will not work with read-only /etc

Status in “isc-dhcp” package in Ubuntu:
  New

Bug description:
  dhclient-script attempts to support read-only root , but it wont correctly work.
  For a read-only root to work, and support dhclient-script writing to /etc/resolv.conf, then /etc/resolv.conf would have to be a symlink to a writeable location (ie, /run).

  To that end, dhclient-script attempts to check and see if / is going
  to be mounted 'rw' and only wait for that case if it is.

  The problem is that it basically has the following logic:
    if root_will_be_mounted_rw; then
        wait-for-writable /etc/
    fi
    new_resolv_conf=/etc/resolv.conf.dhclient-new
    write new file to to $new_resolv_conf
    change attributes of $new_resolv_conf to match resolv.conf
    mv $new_resolv_conf /etc/resolv.conf

  That doesn't work if /etc is read-only and /etc/resolv.conf is a symlink for the following reasons:
   * $new_resolv_conf is being written to /etc/ (and wont be writable)
   * the mv will actually break the symlink and try to create a new file in /etc

  ProblemType: Bug
  DistroRelease: Ubuntu 11.10
  Package: isc-dhcp-client 4.1.1-P1-17ubuntu9
  ProcVersionSignature: Ubuntu 3.0.0-11.18-generic 3.0.4
  Uname: Linux 3.0.0-11-generic x86_64
  ApportVersion: 1.23-0ubuntu1
  Architecture: amd64
  Date: Fri Sep 23 11:50:56 2011
  EcryptfsInUse: Yes
  InstallationMedia: Ubuntu 10.04 "Lucid Lynx" - Beta amd64 (20100318)
  ProcEnviron:
   SHELL=/bin/bash
   PATH=(custom, user)
   LANG=en_US.UTF-8
  SourcePackage: isc-dhcp
  UpgradeStatus: Upgraded to oneiric on 2010-11-15 (311 days ago)

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