linux-kernel - Re: [patch 00/13] vfs: add helpers to check r/o bind mounts

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Message-Id: <200804241729.m3OHTnNx016180@agora.fsl.cs.sunysb.edu>
Date:	Thu, 24 Apr 2008 13:29:49 -0400
From:	Erez Zadok <ezk@...sunysb.edu>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Miklos Szeredi <miklos@...redi.hu>, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, dave@...ux.vnet.ibm.com,
	ezk@...sunysb.edu, mhalcrow@...ibm.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 00/13] vfs: add helpers to check r/o bind mounts 

In message <20080424142857.GF15214@...IV.linux.org.uk>, Al Viro writes:
> On Thu, Apr 24, 2008 at 04:09:18PM +0200, Miklos Szeredi wrote:
[...]
> FWIW, I'm not all that happy about the way ecryptfs_interpose() is done,
> while we are at it.  We get the sucker opened by whoever steps on given
> place in the tree first, with subsequent operations done using the resulting
> struct file.  With fallback to r/o open.  What happens to somebody who
> tries to open it with enough permissions to do r/w?

Yes, ecryptfs_interpose() calls ecryptfs_init_persistent_file() which calls
dentry_open(O_RDWR).  What's the proposed solution for this in the face of
r/o vfsmounts?  How could ecryptfs avoid calling this dentry_open in the
first place?

For unionfs, all I need is return -EROFS or the like to trigger a possible
copyup.

Erez.
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