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

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Message-ID: <20200615164218.GB23493@lst.de>
Date:   Mon, 15 Jun 2020 18:42:18 +0200
From:   Christoph Hellwig <hch@....de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@....de>, 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

On Mon, Jun 15, 2020 at 09:39:31AM -0700, Linus Torvalds wrote:
> 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..

Yes, this would be bug in the calling code.