lkml.org 
[lkml]   [2012]   [Feb]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
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


\
 
 \ /
  Last update: 2012-02-17 18:59    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site