linux-kernel - Re: [PATCH 1/3] autofs4 - fix device ioctl mount lookup

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Date:	Wed, 04 Sep 2013 12:07:28 +0800
From:	Ian Kent <raven@...maw.net>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	rui.xiang@...wei.com, autofs mailing list <autofs@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] autofs4 - fix device ioctl mount lookup

On Wed, 2013-09-04 at 11:53 +0800, Ian Kent wrote:
> On Wed, 2013-09-04 at 03:42 +0100, Al Viro wrote:
> > On Wed, Sep 04, 2013 at 03:26:17AM +0100, Al Viro wrote:
> > > I've applied slightly modified variant of Jeff's "vfs: allow umount to handle
> > > mountpoints without revalidating them" (modified by just leaving the
> > > struct path filled with mountpoint and leaving the equivalent of follow_mount()
> > > to caller) to the local queue and I'm pretty sure that it's what we want
> > > here as well.
> > 
> > ... and killed the modifications since the result ends up uglier for
> > caller(s) anyway.  Reapplied as-is.
> 
> But isn't that what's needed anyway?

Except for the question of following symlinks which is still bugging me.

Granted, the initial implementation (8d7b48e0) didn't check for a
symlink but probably should have and returned EINVAL if it found one.

That's because the whole process is driven by automount maps that have
specific paths, so needing to follow a symlink is an indication the
caller is doing something wrong.

It's probably not actually harmful to cater for it in kernel .... though
the user will likely crash and burn some time later.

> 
> Looks like it fits with the existing code that walks back down looking
> for a match.
> 
> And that fits in with fixing the bug where we want the first match just
> means breaking out early. The match should be close to the top, if not
> the first then the second, for the common case.
> 
> Ian


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