svn commit: r272505 - in head/sys: kern sys

[Bjoern A. Zeeb]

On 04 Oct 2014, at 16:36 , Konstantin Belousov <kostikbel at gmail.com> wrote:

> On Sat, Oct 04, 2014 at 02:21:54PM +0000, Bjoern A. Zeeb wrote:
>> 
>> On 04 Oct 2014, at 08:08 , Mateusz Guzik <mjg at FreeBSD.org> wrote:
>> 
>>> Author: mjg
>>> Date: Sat Oct  4 08:08:56 2014
>>> New Revision: 272505
>>> URL: https://svnweb.freebsd.org/changeset/base/272505
>>> 
>>> Log:
>>> Plug capability races.
>>> 
>>> fp and appropriate capability lookups were not atomic, which could result in
>>> improper capabilities being checked.
>>> 
>>> This could result either in protection bypass or in a spurious ENOTCAPABLE.
>>> 
>>> Make fp + capability check atomic with the help of sequence counters.
>>> 
>>> Reviewed by:	kib
>>> MFC after:	3 weeks
>>> 
>>> Modified:
>>> head/sys/kern/kern_descrip.c
>>> head/sys/sys/filedesc.h
>>> ?
>> 
>> 
>> This file is included from user space.  There is no opt_capsicum.h there.
>> Including an opt_* in the header file seems wrong in a lot of ways usually.
> I think that easiest, and probably the most correct, fix is to include
> the fde_seq member unconditionally.
> 
>> 
>> I tried to add a bandaid for the moment with r272523 which (to be honest) makes it worse.
>> 
>> This needs a better fix.
> Hm, I do see inclusion of sys/filedesc.h in the usermode programs, most
> worrying is libprocstat.  But, there is nothing useful for usermode in the
> header, except possibly for the code with inspects KVA.

It’s included indirectly imho through other sys/* header files  if I am not mistaken.


> 
>> 
>> 
>> I also wonder why the (conditional) fde_seq ended up at the beginning of the structure rather than the end?
>> 
> Why not ?

Because it guarantees the structure layout (offsets) to change for either way, where-as at the end things would at least be deterministic for the beginning;  it might not make a change in reality, but it’s nice anyway (also for debugging).

— 
Bjoern A. Zeeb             "Come on. Learn, goddamn it.", WarGames, 1983