From: Peter Zijlstra <peterz@infradead.org>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jens Axboe <axboe@kernel.dk>,
Elena Reshetova <elena.reshetova@intel.com>,
linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
linux-scsi@vger.kernel.org, linux-btrfs@vger.kernel.org,
gregkh@linuxfoundation.org, fujita.tomonori@lab.ntt.co.jp,
mingo@redhat.com, clm@fb.com, jbacik@fb.com, dsterba@suse.com
Subject: Re: [PATCH 0/5] block subsystem refcounter conversions
Date: Mon, 20 Feb 2017 17:56:39 +0100 [thread overview]
Message-ID: <20170220165639.GE6515@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1487605261.2337.4.camel@HansenPartnership.com>
On Mon, Feb 20, 2017 at 07:41:01AM -0800, James Bottomley wrote:
> On Mon, 2017-02-20 at 08:15 -0700, Jens Axboe wrote:
> > On 02/20/2017 04:16 AM, Elena Reshetova wrote:
> > > Now when new refcount_t type and API are finally merged
> > > (see include/linux/refcount.h), the following
> > > patches convert various refcounters in the block susystem from
> > > atomic_t to refcount_t. By doing this we prevent intentional or
> > > accidental underflows or overflows that can led to use-after-free
> > > vulnerabilities.
>
> This description isn't right ... nothing is prevented; we get warnings
> on saturation and use after free with this.
The thing that is prevented is overflow and then a use-after-free by
making it a leak.
Modular stuff, you put and free at: (n+1) mod n, by saturating at n-1
we'll never get there.
So you loose use-after-free, you gain a resource leak. The general idea
being that use-after-free is a nice trampoline for exploits, leaks are
'only' a DoS.
next prev parent reply other threads:[~2017-02-20 16:56 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-20 11:16 [PATCH 0/5] block subsystem refcounter conversions Elena Reshetova
2017-02-20 11:16 ` [PATCH 1/5] block: convert bio.__bi_cnt from atomic_t to refcount_t Elena Reshetova
2017-02-20 11:16 ` [PATCH 2/5] block: convert blk_queue_tag.refcnt " Elena Reshetova
2017-02-20 11:16 ` [PATCH 3/5] block: convert blkcg_gq.refcnt " Elena Reshetova
2017-02-20 11:16 ` [PATCH 4/5] block: convert io_context.active_ref " Elena Reshetova
2017-02-20 11:16 ` [PATCH 5/5] block: convert bsg_device.ref_count " Elena Reshetova
2017-02-20 15:15 ` [PATCH 0/5] block subsystem refcounter conversions Jens Axboe
2017-02-20 15:41 ` James Bottomley
2017-02-20 15:44 ` Jens Axboe
2017-02-20 16:56 ` Peter Zijlstra [this message]
2017-02-20 17:24 ` James Bottomley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170220165639.GE6515@twins.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=James.Bottomley@HansenPartnership.com \
--cc=axboe@kernel.dk \
--cc=clm@fb.com \
--cc=dsterba@suse.com \
--cc=elena.reshetova@intel.com \
--cc=fujita.tomonori@lab.ntt.co.jp \
--cc=gregkh@linuxfoundation.org \
--cc=jbacik@fb.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-scsi@vger.kernel.org \
--cc=mingo@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.