Messages in this thread | | | Date | Fri, 17 Feb 2012 09:53:22 -0800 | From | Greg KH <> | Subject | Re: [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
| |