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Date:   Tue, 29 Sep 2020 20:00:37 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Ondrej Mosnacek <omosnace@redhat.com>, Ian Kent <raven@themaw.net>,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@lst.de>, autofs@vger.kernel.org,
        Linux Security Module list 
        <linux-security-module@vger.kernel.org>,
        SElinux list <selinux@vger.kernel.org>,
        Zdenek Pytela <zpytela@redhat.com>
Subject: Re: Commit 13c164b1a186 - regression for LSMs/SELinux?
Message-ID: <20200929180037.GA12447@lst.de>
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On Tue, Sep 29, 2020 at 10:23:50AM -0700, Linus Torvalds wrote:
> On Tue, Sep 29, 2020 at 5:16 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> >
> > OK, so it seems that reverting comes out as the best choice here.
> 
> Yeah.
> 
> > BTW, I'm looking at rw_verify_area() and I see this "If (ppos)" check
> > and the comment above it... And then I look at autofs_write(), which
> > passes &file->f_pos, while ksys_write() passes file_ppos(file)
> 
> Ok, that doesn't matter for the security_file_permission() issue, but
> yes, autofs is doing the traditional thing, and it's pointless. Using
> file_ppos(file) isn't an option since it's an inline to read_write.c,
> but it could just pass in NULL these days and avoid that too.
> 
> So how about we just do the appended patch? Can whoever sees this
> problem just verify, even though it looks trivially correct...

This looks sensible to me.  I'd throw in a

/* only for autofs, don't use in new code */

near the export, but users of these kind of functions tend to be
blind copy and paste code anyway, so the comment probably isn't
even read by the relevant parties..