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    SubjectRe: [: Re: [patch 2/8] personality: fix PER_CLEAR_ON_SETID (CVE-2009-1895)]

    On Sun, 19 Jul 2009, Athanasius wrote:
    > And it's that "as long as we ..." that still bothers me. I've *never*
    > had any need for any use of this personality feature and this net/tun.c
    > exploit has proven there can be security gotchas with it.

    I do agree. Some of those features may not be worth the cost.

    That said, this particular feature made sense at the time it was
    implemented. Some people really _did_ care about running SVR4 binaries on
    Linux. There was a time when it was seen as a feature, and important
    enough to work with. So that "map a zero page at NULL" was an important
    thing that we wanted such binaries to be able to depend on.

    These days? We could probably get rid of that idiotic feature. It's simply
    not important enough any more. Does anybody really care? At the same time,
    over years we've grown _other_ personality flags, and some of them are
    still relevant.

    Some binaries are unhappy with address space randomizations. Sometimes
    it's because of outright bugs (that just were hidden by non-randomized VM
    layout) - but that doesn't really help, does it? If you depend on that
    binary, as a user you want the ability to say "run this binary in a mode
    where it works".

    Other binaries are unhappy with address space randomization because they
    need to get the absolute maximum contiguous VM space for some big array.
    Ok, so that's less of an issue in 64-bit mode, but there really are
    programs out there that link everything statically and want to run at a
    low virtual address so that they can get 2.5GB of virtual memory for one
    single big allocation. I've written crap like that myself. I'm not _proud_
    of it, but I could easily see that programs like that could be unhappy if
    the system wiggles mmap's around for security issues.

    So I do agree that we can probably get rid of some really dated
    personality bits. But I don't think we can really get rid of the concept.
    Because compatibility is always of paramount importance.


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