svn commit: r272505 - in head/sys: kern sys
Bjoern A. Zeeb
bz at FreeBSD.org
Sat Oct 4 19:25:56 UTC 2014
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
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