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

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Message-ID: <20160719183327.GA22621@codemonkey.org.uk>
Date:	Tue, 19 Jul 2016 14:33:27 -0400
From:	Dave Jones <davej@...emonkey.org.uk>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	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 05:20:36PM +0100, Al Viro wrote:
 > On Tue, Jul 19, 2016 at 11:31:45AM -0400, Dave Jones wrote:
 > > On Tue, Jul 19, 2016 at 02:16:36PM +0300, Alexey Dobriyan wrote:
 > >  > > BUG: KASAN: use-after-free in proc_map_files_readdir+0x2e3/0x5a0 at addr ffff88044feb2044
 > >  > 
 > >  > Just in case can you addr2line this address or post disassembly?
 > > 
 > > http://codemonkey.org.uk/junk/fs_proc_base.dis.txt
 > > 
 > > Which by my math, looks to be..
 > > 
 > >     7253:       41 8b 87 84 00 00 00    mov    0x84(%r15),%eax
 > >                         info.len = snprintf(info.name,
 > 
 > The entire expression is
 >                         info.len = snprintf(info.name,
 >                                         sizeof(info.name), "%lx-%lx",
 >                                         vma->vm_start, vma->vm_end);
 > and we have
 > 	* address of array field in local structure.
 > 	* constant
 > 	* string literal
 > 	* two longs fetched from *vma, that being done under ->mmap_sem
 > 	* call of snprintf
 > 	* store into a field of local structure.
 > The only ways to get use-after-free in that would be to have *vma freed
 > under you or have the same happen to your stack frame.
 > 
 > 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

	Dave