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    SubjectRe: [kernel-hardening] Re: Add overflow protection to kref
    On Fri, Feb 17, 2012 at 05:44:57PM -0800, Roland Dreier wrote:
    > On Fri, Feb 17, 2012 at 3:39 PM, Djalal Harouni <> wrote:
    > >> 2) what to do with architectures-loosers?
    > > There is lib/atomic64.c but with a static hashed array of raw_spinlocks.
    > Even leaving aside performance impact of atomic64_t (and probably
    > in most cases the performance of kref is not important at all), it is
    > unfortunate to bloat the size from 4 bytes to 8 bytes.
    > It seems much better to have some out-of-line code for overflow
    > checking rather than increasing the size of every data structure
    > that embeds a kref.

    Please realize that kref is an in-line structure now.

    > Greg, I'm not sure why you're opposed to adding this checking...
    > it's pretty clear that buggy error paths that forget to do a put are
    > pretty common and will continue to be common in new code, and
    > making them harder to exploit seems pretty sane to me.
    > What's the downside?

    The downside is that there has not even been a patch sent for any of
    this. Combine that with a lack of understanding about reference
    counting and atomic_t usages in the kernel, and the whole thing is ripe
    for misunderstanding and confusion.

    greg k-h

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      Last update: 2012-02-18 17:27    [W:0.020 / U:0.424 seconds]
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