Messages in this thread | | | Date | Fri, 17 Feb 2012 11:59:45 +0400 | From | Vasiliy Kulikov <> | Subject | Re: [kernel-hardening] Re: Add overflow protection to kref |
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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.
Thanks,
-- Vasiliy
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