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    SubjectRe: [kernel-hardening] Re: Add overflow protection to kref
    On Fri, Feb 17, 2012 at 11:59:45AM +0400, Vasiliy Kulikov wrote:
    > Hi,
    >
    > > And in all that time, I've never seen an instance where you can overflow
    > > the reference count,
    >
    > Do you mean that the overflow is theoretically impossible or that this
    > type of programmer error is rare?
    >
    > If the former, it is only 2**32 incs - if you can find open() implementation
    > with a missing atomic_dec() in error path and you can call open() faster than
    > 10000 times per second, you can overflow the counter in ~4 days.
    >
    > If the latter, it is just a question of finding missing put() in some triggerable
    > error path. Kees has already posted a link to a bug with a missing fput().
    >
    >
    > BTW, moving from atomic_t to 64 bit refcounter would kill the possibility of
    > overflow. Unfortunately, AFAIU, 64 bit operations are not atomic on some 64 bit
    > archs.

    Can we switch it on those arches where it is an atomic operation? That
    would be a nice simple solution.

    thanks,

    greg k-h


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