linux-kernel - Re: [RFC][PATCHES] iov

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Message-ID: <20141208181401.GD22149@ZenIV.linux.org.uk>
Date:	Mon, 8 Dec 2014 18:14:04 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [RFC][PATCHES] iov_iter.c rewrite

On Mon, Dec 08, 2014 at 10:07:55AM -0800, Linus Torvalds wrote:

> Which is in the vmalloc address space. So somebody used a vmalloc'ed
> address and tried to convert it to a physical address in order to look
> up the page.
> 
> Which is not a valid operation, and the BUG_ON() is definitely proper.
> 
> Now *why* something tried to do a virt_to_page() on a vmalloc'ed
> address, that I leave to others.

iov_iter_get_pages() in ITER_KVEC case, trying to avoid get_user_pages_fast()
and getting it wrong.  FWIW, the reproducer is finit_module(fd, ....)
where fd has been opened with O_DIRECT.  In that case we get kernel_read()
on O_DIRECT and the buffer has just been vmalloc'ed.

What's the sane way to grab struct page * for a vmalloc'ed address?
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