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

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Date:	Wed, 30 Sep 2015 17:30:17 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Al Viro <viro@...IV.linux.org.uk>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>, willy@...ux.intel.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 09/17/2015 10:24 PM, Sasha Levin wrote:
> On 08/19/2015 01:46 AM, Al Viro wrote:
>>> 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...
>>
> 
> So I've traced this all the way back to dax_io(). I can trigger this with:
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 93bf2f9..2cdb8a5 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -178,6 +178,7 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
>         if (need_wmb)
>                 wmb_pmem();
> 
> +       WARN_ON((pos == start) && (pos - start > iov_iter_count(iter)));
>         return (pos == start) ? retval : pos - start;
>  }
> 
> So it seems that iter gets moved twice here: once in dax_io(), and once again
> back at generic_file_read_iter().
> 
> I don't see how it ever worked. Am I missing something?

Ping?


Thanks,
Sasha

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