linux-kernel - Re: [PATCH RESEND] splice: introduce FMODE_SPLICE_READ and FMODE_SPLICE

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Message-ID: <20170111130008.GE6286@linux-x5ow.site>
Date:   Wed, 11 Jan 2017 14:00:08 +0100
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Jeff Layton <jlayton@...hat.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        mbenes@...e.cz, jack@...e.cz
Subject: Re: [PATCH RESEND] splice: introduce FMODE_SPLICE_READ and
 FMODE_SPLICE_WRITE

On Wed, Jan 11, 2017 at 07:20:13AM -0500, Jeff Layton wrote:
> On Wed, 2017-01-11 at 10:51 +0100, Johannes Thumshirn wrote:
> > Introduce FMODE_SPLICE_READ and FMODE_SPLICE_WRITE. These modes check
> > whether it is legal to read or write a file using splice. Both get
> > automatically set on regular files and are not checked when a 'struct
> > fileoperations' includes the splice_{read,write} methods.
> > 
> 
> Could you add a description of the problem that this solves? I assume
> you hit a problem trying to splice to/from a non-regular file, but it'd
> be good to know what that problem was.

The problem is that a driver's ->write() is called under KERNEL_DS this way.
This happened for sg and bsg and caused 128394eff 'sg_write()/bsg_write() is
not fit to be called under KERNEL_DS' as well as a0ac402cf 'Don't feed
anything but regular iovec's to blk_rq_map_user_iov'.

There have also been patches for InfiniBand AFAIR doing similar things.

So this is to solve it for future abuses.

HTH,
	Johannes
-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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