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From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Jordy Zomer <jordy@pwning.systems>, Kees Cook <keescook@chromium.org>
Cc: 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 12:40:26 -0700	[thread overview]
Message-ID: <68d2b3afd9a7ee27cdb7ec9ff7eb45342ce23c12.camel@HansenPartnership.com> (raw)
In-Reply-To: <209705133.1285234.1629477520318@privateemail.com>

On Fri, 2021-08-20 at 12:38 -0400, Jordy Zomer wrote:
> Hi There!
> 
> Because this is a global variable, it appears to be exploitable.
> Either we generate a sufficient number of processes to achieve this
> counter, or you increase the open file limit with ulimit or sysctl.
> Unless the kernel has a hard restriction on the number of potential
> file descriptors that I'm not aware of.

There's no direct global counter for file descriptors, no; however,
there is an indirect limit: the number of processes per user which is
now defaulting to around 65535, so even a fork bomb opening the max
number of fds won't get you a wrap.

> In any case, it's probably a good idea to patch this to make it
> explicitly secure. If you discover a hard-limit in the kernel for
> open file descriptors, please let me know. I'm genuinely interested
> :D!

I didn't disagree it might be a useful think to update ... I just
didn't think it was currently exploitable.

James



      reply	other threads:[~2021-08-20 19:40 UTC|newest]

Thread overview: 9+ 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 14:57   ` James Bottomley
2021-08-20 16:05   ` Kees Cook
2021-08-20 16:38     ` Jordy Zomer
2021-08-20 19:40       ` James Bottomley [this message]

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