linux-kernel - Re: [PATCH] fuse: Add support for fuse stacked I/O

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Message-ID: <56A0133B.9090501@codeaurora.org>
Date:	Wed, 20 Jan 2016 15:07:39 -0800
From:	Nikhilesh Reddy <reddyn@...eaurora.org>
To:	Jann Horn <jannhorn@...glemail.com>
CC:	Miklos Szeredi <miklos@...redi.hu>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	gregkh@...uxfoundation.org, torvalds@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
	Richard Weinberger <richard.weinberger@...il.com>,
	Theodore Ts'o <tytso@....edu>, jack@...e.cz,
	Antonio SJ Musumeci <trapexit@...wn.link>, sven.utcke@....de,
	Nikolaus Rath <nikolaus@...h.org>
Subject: Re: [PATCH] fuse: Add support for fuse stacked I/O

On 01/18/2016 07:07 PM, Jann Horn wrote:
> 2016-01-14 0:53 GMT+01:00 Nikhilesh Reddy <reddyn@...eaurora.org>:
>> Add support for filesystem stacked read/write of files
>> when enabled through a userspace init option of FUSE_STACKED_IO.
>>
>> When FUSE_STACKED_IO is enabled all the reads and writes
>> to the fuse mount point go directly to the native filesystem
>> rather than through the fuse daemon. All requests that aren't
>> read/write still go thought the userspace code.
>
> Maybe I missed it, but how does this guard against kernel stack
> overflow and how does it interact with the "sb->s_stack_depth >
> FILESYSTEM_MAX_STACK_DEPTH" stacking limit that overlayfs and ecryptfs
> use?
>
> As far as I can tell from a quick glance, someone could just stack
> lots of FUSE files on top of each other and cause kernel stack
> overflow that way, and that's nasty.
>
Hi
Thanks so much for your comment and for catching this.
I have fixed the code to prevent further stacking and will send it out 
in the updated version of the patch ( now called fuse passthrough ).

-- 
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.