linux-kernel - Re: [PATCH] early init: open /dev/console with O

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Message-ID: <20200102175300.GA292871@light.dominikbrodowski.net>
Date:   Thu, 2 Jan 2020 18:53:00 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        youling 257 <youling257@...il.com>
Subject: Re: [PATCH] early init: open /dev/console with O_LARGEFILE

On Wed, Jan 01, 2020 at 01:39:00PM -0800, Linus Torvalds wrote:
> I'm not saying that the revert is wrong at this point,

Linus, I'd like you to revert the patch nonetheless -- it was quite broken,
it is still broken and probably needs, besides your fix, the O_LARGEFILE
patch I sent out a few days ago.

What is more, I think a different approach is saner, leads to smaller code,
and creates far less risks. And maybe Al Viro likes it a bit more as well :)

At

	https://git.kernel.org/pub/scm/linux/kernel/git/brodo/linux.git ksys-next

there are a few proof-of-concept patches for three in-kernel-syscalls:

(1) Both ksys_open() and ksys_unlink() can trivially operate properly on a
kernelspace pointer (by means of calling getname_kernel() instead of
getname()), such as:

-static inline long ksys_unlink(const char __user *pathname)
+/* note: operates on a kernelspace pointer to pathname */
+static inline long ksys_unlink(const char *pathname)
 {
-       return do_unlinkat(AT_FDCWD, getname(pathname));
+       return do_unlinkat(AT_FDCWD, getname_kernel(pathname));
 }

(with all callers of ksys_unlinked() checked, of course).

(2) For ksys_mkdir(), we already have a fully vfs-in-kernelspace variant in
devtmpfs::dev_mkdir(), which we can use for ksys_mkdir() as well.

What do you (and others) think of these alternative approaches? If we should
work in this direction, please revert the patch -- the new patches should go
into v5.6 at earliest, and probably be routed via Al Viro (unless he and/or
you want me to have this tree managed independently, and included in
linux-next separately).

Thanks,
	Dominik