linux-kernel - Re: *sigh* /proc/*/pagemap

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Message-ID: <20080717201703.GA23775@martell.zuzino.mipt.ru>
Date:	Fri, 18 Jul 2008 00:17:03 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	akpm@...l.org, mpm@...enic.com
Cc:	linux-kernel@...r.kernel.org, pagexec@...email.hu
Subject: Re: *sigh* /proc/*/pagemap

> > >> 5) check with microscope allocation there -- page-aligned address and
> > size
> > >> == 0
> > >>     should allocate 0 bytes, and
> > >
> > > Where?
> >
> > kmalloc() in pagemap_read(). kmalloc(0)  and integer wraparound look
> > possible.

Now that I unsuccessfully tried to reproduce multiplication wraparound (on 32-bit),
integer wraparound in kmalloc() simply can't happen here.

Relevant code from pagemap_read():

	uaddr = (unsigned long)buf & PAGE_MASK;
	uend = (unsigned long)(buf + count);
	pagecount = (PAGE_ALIGN(uend) - uaddr) / PAGE_SIZE;
	pages = kmalloc(pagecount * sizeof(struct page *), GFP_KERNEL);


pagecount is effectively "count / PAGE_SIZE", where "count" is size_t.
kmalloc() takes size_t as first argument, so one has to overflow

	count / PAGE_SIZE * sizeof(pointer).

For sure, page is bigger than pointer.

Anyone still see holes?

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