linux-kernel - Re: [RFC 0/3] iommu/iova: Unsafe locking in find

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1530886247.3205.53.camel@arista.com>
Date:   Fri, 06 Jul 2018 15:10:47 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     linux-kernel@...r.kernel.org,
        David Woodhouse <dwmw2@...radead.org>,
        iommu@...ts.linux-foundation.org,
        Dmitry Safonov <0x7f454c46@...il.com>
Subject: Re: [RFC 0/3] iommu/iova: Unsafe locking in find_iova()

On Fri, 2018-07-06 at 15:16 +0200, Joerg Roedel wrote:
> On Thu, Jun 21, 2018 at 07:08:20PM +0100, Dmitry Safonov wrote:
> > find_iova() looks to be using a bad locking practice: it locks the
> > returned iova only for the search time.  And looking in code, the
> > element can be removed from the tree and freed under rbtree lock.
> > That
> > happens during memory hot-unplug and cleanup on module
> > removal.  Here
> > I cleanup users of the function and delete it.
> 
> But this is only a problem if more than one code-path uses tries to
> handle a given iova at the same time, no?

Yes, as far as I can see, there are code-paths which may try to handle
it at the same time:
o memory notifiers for hot-unplug (intel-iommu.c)
o drivers unloading calls free_iova(), which in the result calls
  find_iova()
o I see at least one driver that frees iova during it's normal work
  too: scif_rma.c:scif_free_window_offset()

So, I decided to fix the interface while it's not widely used instead
of all callers.
Looks worth for me even as it's all corner-cases like unplugging the
memory.

Anyway, just found it while some college wrote a debug sysfs interface
for iovas and used find_iova().
So, if you think it's not worth to change - that's fine for me, but I
thought I'll nip this in the bud, preventing other people to misuse it.

-- 
Thanks,
             Dmitry