linux-kernel - Re: [PATCH] afs: proc cells and rootcell are writeable

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Message-ID: <20140128202754.GI10323@ZenIV.linux.org.uk>
Date:	Tue, 28 Jan 2014 20:27:54 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	David Howells <dhowells@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-afs@...ts.infradead.org, Pali Roh??r <pali.rohar@...il.com>
Subject: Re: [PATCH] afs: proc cells and rootcell are writeable

On Tue, Jan 28, 2014 at 08:20:12PM +0000, David Howells wrote:
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > > -       p = proc_create("cells", 0, proc_afs, &afs_proc_cells_fops);
> > > +       p = proc_create("cells", S_IFREG | S_IRUGO | S_IWUSR, proc_afs, &afs_proc_cells_fops);
> > > -       p = proc_create("rootcell", 0, proc_afs, &afs_proc_rootcell_fops);
> > > +       p = proc_create("rootcell", S_IFREG | S_IRUGO | S_IWUSR, proc_afs, &afs_proc_rootcell_fops);
> > 
> > So the S_IFREG isn't necessary.
> 
> True.  Is it worth creating proc_create_special() that can create a non-regular
> file and then making proc_create() only permit regular files (and complain if
> the S_IFMT field is not zero)?

We already do: in proc_create_data() we have
        struct proc_dir_entry *pde;
        if ((mode & S_IFMT) == 0)
                mode |= S_IFREG;

        if (!S_ISREG(mode)) {
                WARN_ON(1);     /* use proc_mkdir() */
                return NULL;
        }

proc_mkdir{,_data,_mode} are there for purpose.  Nobody had been insane
enough to put FIFOs or sockets in procfs and anything else would need
additional data anyway.  proc_symlink() is there, proc_mknod() isn't and
nobody has complained yet.  Let's keep it that way, plese...
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