linux-kernel - RE: [PATCH 05/13] fs: check FMODE_WRITE in __kernel

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Date:   Wed, 17 Jun 2020 14:59:39 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>
CC:     Al Viro <viro@...iv.linux.org.uk>, Ian Kent <raven@...maw.net>,
        "David Howells" <dhowells@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        NetFilter <netfilter-devel@...r.kernel.org>
Subject: RE: [PATCH 05/13] fs: check FMODE_WRITE in __kernel_write

From: Linus Torvalds
> Sent: 15 June 2020 17:40
> On Mon, Jun 15, 2020 at 5:13 AM Christoph Hellwig <hch@....de> wrote:
> >
> > We still need to check if the fѕ is open write, even for the low-level
> > helper.
> 
> Is there actually a way to trigger something like this? I'm wondering
> if it's worth a WARN_ON_ONCE()?
> 
> It doesn't sound sensible to have some kernel functionality try to
> write to a file it didn't open for write, and sounds like a kernel bug
> if this case were to ever trigger..

It's a cheap test at the top of some fairly heavy code.
Failing the request will soon identify the bug.

	David

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