linux-kernel - Re: [BUG] binfmt_elf: get_user() called in vma_dump_size() after set_fs(KERNEL

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Date:	Fri, 6 Feb 2009 13:44:10 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Gerald Schaefer <gerald.schaefer@...ibm.com>
Cc:	roland@...hat.com, linux-kernel@...r.kernel.org,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	torvalds@...ux-foundation.org
Subject: Re: [BUG] binfmt_elf: get_user() called in vma_dump_size() after
 set_fs(KERNEL_DS)

On Fri, 06 Feb 2009 18:10:35 +0100
Gerald Schaefer <gerald.schaefer@...ibm.com> wrote:

> Hi,
> 
> elf_core_dump() does a set_fs(KERNEL_DS) and then calls vma_dump_size(),
> which uses get_user() to check for an ELF header at vma->vm_start in the
> user mapping. This is a bug because vm_start is a user virtual address and
> get_user() will fail or even read from a kernel address (KERNEL_DS).
> 
> Maybe a get_user_pages() should be used to get the user data, or a temporary
> set_fs(USER_DS)?
> 

Could use __get_user() to skip the access_ok() check?

We'd need to be sure that the address isn't a kernel address or iomem
or something. 
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