From: Matthew Wilcox <willy@infradead.org>
To: Daniel Micay <danielmicay@gmail.com>
Cc: Jann Horn <jannh@google.com>,
linux-mm@kvack.org,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
kernel list <linux-kernel@vger.kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFC] Warn the user when they could overflow mapcount
Date: Thu, 8 Feb 2018 12:21:00 -0800 [thread overview]
Message-ID: <20180208202100.GB3424@bombadil.infradead.org> (raw)
In-Reply-To: <CA+DvKQKba0iU+tydbmGkAJsxCxazORDnuoe32sy-2nggyagUxQ@mail.gmail.com>
On Thu, Feb 08, 2018 at 02:48:52PM -0500, Daniel Micay wrote:
> I guess it could saturate and then switch to tracking the count via an
> object pointer -> count mapping with a global lock? Whatever the
> solution is should probably be a generic one since it's a recurring
> issue.
I was thinking of saturating _mapcount at 2 billion (allowing _refcount
the extra space to go into the 2-3 billion range). Once saturated,
disallow all attempts at mapping it until _mapcount has gone below 2
billion again. We can walk the page->mapping->i_mmap tree and find
tasks with more than, say, 10 mappings each, and kill them.
Now that I think about it, though, perhaps the simplest solution is not
to worry about checking whether _mapcount has saturated, and instead when
adding a new mmap, check whether this task already has it mapped 10 times.
If so, refuse the mapping.
Now we can argue that since pid_max is smaller than 400 million that
_mapcount will never overflow, and so we don't need to check it.
Convincing argument?
next prev parent reply other threads:[~2018-02-08 20:21 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-08 2:11 [RFC] Warn the user when they could overflow mapcount Matthew Wilcox
2018-02-08 2:56 ` Jann Horn
2018-02-08 4:04 ` Matthew Wilcox
2018-02-08 17:58 ` valdis.kletnieks
2018-02-08 18:05 ` Daniel Micay
2018-02-08 18:56 ` Matthew Wilcox
2018-02-08 19:33 ` Daniel Micay
2018-02-08 19:42 ` Matthew Wilcox
2018-02-08 19:48 ` Daniel Micay
2018-02-08 20:21 ` Matthew Wilcox [this message]
2018-02-08 21:37 ` [RFC] Limit mappings to ten per page per process Matthew Wilcox
2018-02-09 4:26 ` Kirill A. Shutemov
2018-02-14 13:51 ` Matthew Wilcox
2018-02-14 14:05 ` Kirill A. Shutemov
2018-02-09 1:47 ` [RFC] Warn the user when they could overflow mapcount Daniel Micay
2018-02-08 3:18 ` Tobin C. Harding
2018-02-08 4:06 ` Matthew Wilcox
2018-03-02 21:26 ` [RFC] Handle mapcount overflows Matthew Wilcox
2018-03-02 22:03 ` Matthew Wilcox
2019-05-01 14:41 ` Jann Horn
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