linux-kernel - Re: [WTF] ... is going on with current->fs->{root,mnt} accesses in pohmelfs

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Message-ID: <20100210101246.GA3509@ioremap.net>
Date:	Wed, 10 Feb 2010 13:12:46 +0300
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [WTF] ... is going on with current->fs->{root,mnt} accesses in pohmelfs

On Wed, Feb 10, 2010 at 10:04:28AM +0000, Al Viro (viro@...IV.linux.org.uk) wrote:
> a) pohmelfs_construct_path_string() will do interesting things if you
> call it while chrooted into jail and pohmelfs mounted deeper in that
> jail.  Try it.

Should it walk upto mountpoint?

> b) just why do we care about root of chroot jail in pohmelfs_path_length()?
> Not to mention anything else, current->fs->root/mnt may be changed under
> you if you share current->fs with another thread, but even aside of that,
> why does filesystem care about chroot of caller at all?
> 
> What's going on there?

It tries to construct a full path upto mountpoint. Effectively it should
do similar to non-exported dentry_path() things. There is a race between
getting buffer size and filling with the actual path, but we take care
about that by restarting if needed.

-- 
	Evgeniy Polyakov
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