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    SubjectRe: thoughts on kernel security issues
    Linus Torvalds <> said:
    > 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.

    But you can trivially run an executable via e.g.:

    /lib/ some-nice-proggie

    and the execute permissions (and noexec, etc) on some-nice-proggie don't

    > Am I claiming that disallowing self-written ELF binaries gets rid of all
    > security holes? Obviously not.

    It makes their running a bit harder, but not much.

    > 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.

    Right. But this is a broken idea, IMVHO.

    Besides, something that has been overlooked in all this discussion so far:
    It does routinely happen that fixing some "just an ordinary bug" really
    does correct a security problem. Plus backporting "only security fixes"
    gets harder and harder as they start depending on other random changes.
    Dr. Horst H. von Brand User #22616
    Departamento de Informatica Fono: +56 32 654431
    Universidad Tecnica Federico Santa Maria +56 32 654239
    Casilla 110-V, Valparaiso, Chile Fax: +56 32 797513
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