linux-kernel - Re: 4.7-rc7: use-after-free in proc_map_files

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Message-ID: <20160719193857.GI2356@ZenIV.linux.org.uk>
Date:	Tue, 19 Jul 2016 20:38:57 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dave Jones <davej@...emonkey.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 4.7-rc7: use-after-free in proc_map_files_readdir

On Tue, Jul 19, 2016 at 02:33:27PM -0400, Dave Jones wrote:
>  > Could you dump the relevant part of vmlinux objdump, rather than whatever
>  > you've used on base.o?  Having relocations resolved makes it much easier
>  > to figure out...  Or just dump that vmlinux on anonftp somewhere...
> 
> http://codemonkey.org.uk/junk/vmlinux.gz

OK, it's actually about fetching ->f_mode in
                        info.mode = vma->vm_file->f_mode;

%r15 points contains vma->vm_file at that point, and 0x84 is the offset of
f_mode in struct file on your config from hell (due to spinlock_t size
exploding on lockdep et.al.)

Interesting...  Do you have a reproducer for that?