lkml.org 
[lkml]   [2012]   [Feb]   [18]   [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 05:44:57PM -0800, Roland Dreier wrote:
> On Fri, Feb 17, 2012 at 3:39 PM, Djalal Harouni <tixxdz@opendz.org> 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


\
 
 \ /
  Last update: 2012-02-18 17:27    [W:2.990 / U:0.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site