linux-kernel - Re: WARNING in __kernel

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Message-ID: <20200928221441.GF1340@sol.localdomain>
Date:   Mon, 28 Sep 2020 15:14:41 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     David Laight <David.Laight@...lab.com>,
        syzbot+51177e4144d764827c45@...kaller.appspotmail.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: WARNING in __kernel_read (2)

On Sat, Sep 26, 2020 at 01:17:04PM +0000, David Laight wrote:
> From: David Laight
> > Sent: 26 September 2020 12:16
> > To: 'syzbot' <syzbot+51177e4144d764827c45@...kaller.appspotmail.com>; linux-fsdevel@...r.kernel.org;
> > linux-kernel@...r.kernel.org; syzkaller-bugs@...glegroups.com; viro@...iv.linux.org.uk
> > Subject: RE: WARNING in __kernel_read (2)
> > 
> > > From: syzbot <syzbot+51177e4144d764827c45@...kaller.appspotmail.com>
> > > Sent: 26 September 2020 03:58
> > > To: linux-fsdevel@...r.kernel.org; linux-kernel@...r.kernel.org; syzkaller-bugs@...glegroups.com;
> > > viro@...iv.linux.org.uk
> > > Subject: WARNING in __kernel_read (2)
> > 
> > I suspect this is calling finit_module() on an fd
> > that doesn't have read permissions.
> 
> Code inspection also seems to imply that the check means
> the exec() also requires read permissions on the file.
> 
> This isn't traditionally true.
> suid #! scripts are particularly odd without 'owner read'
> (everyone except the owner can run them!).

Christoph, any thoughts here?  You added this WARN_ON_ONCE in:

	commit 61a707c543e2afe3aa7e88f87267c5dafa4b5afa
	Author: Christoph Hellwig <hch@....de>
	Date:   Fri May 8 08:54:16 2020 +0200

	    fs: add a __kernel_read helper