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    SubjectRe: [PATCH 0/4] coredump: core dump masking support v3

    Markus Gutschke wrote:

    > Kawai, Hidehiro wrote:
    >> This patch series is version 3 of the core dump masking feature,
    >> which provides a per-process flag not to dump anonymous shared
    >> memory segments.
    > I just wanted to remind you that you need to be careful about dumping
    > the [vdso] segment no matter whether you omit other segments. I didn't
    > actually try running your patches, and if the kernel doesn't actually
    > consider this segment anonymous and shared, things might already work
    > fine as is.

    Thank you for your advice and sorry for not replying soon.

    Fortunately, the latest kernel uses VM_ALWAYSDUMP flag to always dump
    the vdso segment. My patchset doesn't change this behavior. So we
    don't need to worry about the vdso segment.

    > As an alternative to your kernel patch, you could achieve the same goal
    > in user space, by linking my coredumper
    > into your binaries and
    > setting up appropriate signal handlers. An equivalent patch for
    > selectively omitting memory regions would be trivial to add.

    As far as I can see, google-coredumper has more flexibility.
    Can google-coredumper satisfy the following requirements easily?

    Requirements are:
    (1) a user can change the core dump settings _anytime_
    - sometimes want to dump anonymous shared memory segments and
    sometimes don't want to dump them
    (2) a user can change the core dump settings of _any processes_
    (although permission checks are performed)
    - in a huge application which forks many processes, a user
    hopes that some processes dump anonymous shared memory
    segments and some processes don't dump them

    And reliability of the core dump feature is also important.

    > While this
    > does give you more flexibility, it of course has the drawback of
    > requiring you to change your applications, so there still is some
    > benefit in a kernelspace solution.

    And all the software vendors don't necessarily apply
    google-coredumper. If the vendor doesn't apply it, the user will
    be bothered by huge core dumps or the buggy application which
    remains unfixed. So I believe that in kernel solution is still

    Hidehiro Kawai
    Hitachi, Ltd., Systems Development Laboratory

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