linux-kernel - Re: fs: out of bounds on stack in iov_iter

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Date:	Wed, 02 Sep 2015 16:00:05 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Al Viro <viro@...IV.linux.org.uk>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>
CC:	Chuck Ebbert <cebbert.lkml@...il.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: fs: out of bounds on stack in iov_iter_advance

On 08/19/2015 01:46 AM, Al Viro wrote:
> On Mon, Aug 17, 2015 at 12:18:12PM +0300, Andrey Ryabinin wrote:
> 
>> This bug is similar to recently found bug in 9p: http://thread.gmane.org/gmane.linux.kernel/1931799/focus=1936542
> 
> Ow.  For those who'd missed that fun: the bug in question had turned out to
> be caused by improper reuse of request ids, _not_ in the call chain of
> the triggering syscall.
> 
>> 	if (!retval) {
>> 		struct iov_iter data = *iter;
>> 		retval = mapping->a_ops->direct_IO(iocb, &data, pos);
>> 	}
>>
>> 	if (retval > 0) {
>> 		*ppos = pos + retval;
>> 		iov_iter_advance(iter, retval);
>>
>>
>> So either filemap_write_and_wait_range()
> 	Shouldn't - it's supposed to return 0 or -E...
> 
>> or mapping->a_ops->direct_IO() returned more
>> than 'count'.
> 
> 	Was there DAX involved?  ->direct_IO() in there is blkdev_direct_IO(),
> which takes rather different paths in those cases...

I don't think so, at least I didn't configure it in.

>>> Also too the file and line number
>>> (lib/iov_iter.c:511) are completely useless because of inlining,
>>> though that's not kasan's fault.
> 
> Might make sense to slap
> 	if (WARN_ON(size > iov_iter_count(i)))
> 		print size and *i
> and see if it triggers...

It finally reproduced. size == 0x1000000, iov_iter_count(iter) == 0x1234.


Thanks,
Sasha

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