[lkml]   [2012]   [Feb]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [kernel-hardening] Re: Add overflow protection to kref

> 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



 \ /
  Last update: 2012-02-17 09:07    [W:0.101 / U:0.928 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site