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

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Message-ID: <CAK9i0=ojVmbuDiFXY_sHA12vTWgz9aKwEQuZmmYtUka3zqr=hg@mail.gmail.com>
Date:	Tue, 19 Jan 2016 04:07:03 +0100
From:	Jann Horn <jannhorn@...glemail.com>
To:	Nikhilesh Reddy <reddyn@...eaurora.org>
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

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.