From: Kees Cook <keescook@chromium.org>
To: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: Jordy Zomer <jordy@pwning.systems>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [PATCH] mm/secretmem: use refcount_t instead of atomic_t
Date: Fri, 20 Aug 2021 09:05:05 -0700 [thread overview]
Message-ID: <202108200904.81ED4AA52@keescook> (raw)
In-Reply-To: <0874a50b61cfaf7c817cab7344c49c1641c1fd10.camel@HansenPartnership.com>
On Fri, Aug 20, 2021 at 07:57:25AM -0700, James Bottomley wrote:
> On Fri, 2021-08-20 at 06:33 +0200, Jordy Zomer wrote:
> > As you can see there's an `atomic_inc` for each `memfd` that is
> > opened in the `memfd_secret` syscall. If a local attacker succeeds to
> > open 2^32 memfd's, the counter will wrap around to 0. This implies
> > that you may hibernate again, even though there are still regions of
> > this secret memory, thereby bypassing the security check.
>
> This isn't a possible attack, is it? secret memory is per process and
> each process usually has an open fd limit of 1024. That's not to say
> we shouldn't have overflow protection just in case, but I think today
> we don't have a problem.
But it's a _global_ setting, so it's still possible, though likely
impractical today. But refcount_t mitigates it and is a trivial change.
:)
--
Kees Cook
next prev parent reply other threads:[~2021-08-20 16:11 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-20 4:33 [PATCH] mm/secretmem: use refcount_t instead of atomic_t Jordy Zomer
2021-08-20 5:33 ` Kees Cook
2021-08-24 14:05 ` Mike Rapoport
2021-10-21 9:00 ` Dmitry Vyukov
2021-08-20 14:57 ` James Bottomley
2021-08-20 16:05 ` Kees Cook [this message]
2021-08-20 16:38 ` Jordy Zomer
2021-08-20 19:40 ` James Bottomley
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