linux-kernel - Re: [PATCH] fs: Allow opening only regular files during execve().

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Date:   Mon, 21 Jan 2019 21:18:01 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Eric Biggers <ebiggers3@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        syzbot 
        <bot+e93a80c1bb7c5c56e522461c149f8bf55eab1b2b@...kaller.appspotmail.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH] fs: Allow opening only regular files during execve().

On Mon, Jan 21, 2019 at 07:14:39PM +0900, Tetsuo Handa wrote:
> On Tue, Dec 12, 2017 at 2:06 PM, Eric Biggers <ebiggers3@...il.com> wrote:
> > I'm not sure what the fix will be.  Maybe the proc handlers should take a
> > different lock instead of cred_guard_mutex.  Or perhaps execve should check that
> > the file is a regular file before it attempts to open it.
> 
> We can easily distinguish open() from execve() and open() from others. ;-)

> +	/* The file or a script interpreter has to be a regular file. */
> +	if (unlikely(current->in_execve && !S_ISREG(inode->i_mode))) {
> +		error = -EACCES;
> +		goto cleanup_file;
> +	}

We are *NOT* going to use current->in_execve to propagate that information.
Come up with a cleaner solution, if you care, but this one is a non-starter.
Too ugly to live.  Sorry.