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Date: Mon, 21 Apr 2014 17:30:58 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, "Theodore Ts'o" <tytso@mit.edu>,
        David Herrmann <dh.herrmann@gmail.com>
Subject: Re: [RFC 2/2] fs,proc: Respect FMODE_WRITE when opening
 /proc/pid/fd/N
Message-ID: <20140421163058.GS18016@ZenIV.linux.org.uk>
References: <cover.1398097304.git.luto@amacapital.net>
 <430cfc67aae9b9ad5eab4d293107285ad44c5fd9.1398097304.git.luto@amacapital.net>
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On Mon, Apr 21, 2014 at 09:22:48AM -0700, Andy Lutomirski wrote:

> +static int proc_may_follow(struct nameidata *nd, struct file *f)
> +{
> +	if (!nd)
> +		return 0;  /* This is readlink, */
> +
> +	if ((nd->flags & LOOKUP_WRITE) && !(f->f_mode & FMODE_WRITE))
> +		return -EACCES;
> +
> +	return 0;
> +}

And this is just plain wrong.  WTF are you making the traversal of symlink
in the middle of pathname dependent on the open flags?

NAK.