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  1. OpenVZ
  2. OVZ-5328

make kernel.dmesg_restrict sysctl container-aware

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    Details

    • Type: Feature Request
    • Status: Closed
    • Priority: Minor
    • Resolution: Fixed
    • Fix Version/s: OpenVZ-legacy
    • Component/s: Containers::Kernel
    • Security Level: Public
    • Environment:
      Operating System: All
      Platform: All

      Description

      Hi,

      The kernel.dmesg_restrict sysctl was added to mainline kernels and backported to RHEL5 and RHEL6 by Red Hat. One of its primary purposes was to protect in-kernel addresses from being shown to non-root users and thus hopefully to make exploitation of certain kinds of kernel bugs more difficult or/and less reliable.

      With OpenVZ containers, however, the in-container dmesg is usually empty, and only sometimes it contains useful info: that container's iptables -j LOG output.

      The attached patch makes kernel.dmesg_restrict tri-state:

      0: no restriction;
      1: non-root users can't access dmesg, root users on both hardware node and in containers can access dmesg (seeing different log records as appropriate);
      2: non-root users and any user and root in containers can't access dmesg, only root on the hardware node can access dmesg.

      2 corresponds to behavior currently seen with 1, whereas the behavior with 1 becomes more relaxed. 1 is then a reasonable default setting for a distro (that's what we use on Owl now).

      Please consider applying this change to your currently maintained kernel branches.

      Thanks,

      Alexander

        Attachments

        1. diff-rh5-dmesg_restrict-description
          0.9 kB
          Vasily Averin
        2. dmesg_restrict.diff
          3 kB
          Solar Designer
        3. openvz-dmesg_restrict-doc.diff
          2 kB
          Solar Designer

          Activity

            People

            Assignee:
            vvs Vasily Averin
            Reporter:
            solar@openwall.com Solar Designer
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              Created:
              Updated:
              Resolved: