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    SubjectRe: thoughts on kernel security issues


    On Thu, 13 Jan 2005, Alan Cox wrote:
    >
    > On Iau, 2005-01-13 at 16:38, Linus Torvalds wrote:
    > > It wouldn't be a global flag. It's a per-process flag. For example, many
    > > people _do_ need to execute binaries in their home directory. I do it all
    > > the time. I know what a compiler is.
    >
    > noexec has never been worth anything because of scripts. Kernel won't
    > load that binary, I can write a script to do it.

    Scripts can only do what the interpreter does. And it's often a lot harder
    to get the interpreter to do certain things. For example, you simply
    _cannot_ get any thread race conditions with most scripts out there, nor
    can you generally use magic mmap patterns.

    Am I claiming that disallowing self-written ELF binaries gets rid of all
    security holes? Obviously not. I'm claiming that there are things that
    people can do that make it harder, and that _real_ security is not about
    trusting one subsystem, but in making it hard enough in many independent
    ways that it's just too effort-intensive to attack.

    It's the same thing with passwords. Clearly any password protected system
    can be broken into: you just have to guess the password. It then becomes a
    matter of how hard it is to "guess" - at some point you say a password is
    secure not because it is a password, but because it's too _expensive_ to
    guess/break.

    So all security issues are about balancing cost vs gain. I'm convinced
    that the gain from openness is higher than the cost. Others will disagree.

    Linus
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