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

[Michael Halcrow <mhalcrow@us.ibm.com>]

On Thu, Apr 24, 2008 at 03:40:03PM -0400, Erez Zadok wrote:
> Ah, I see.  Yes: ecryptfs_init_persistent_file does have this odd
> "try to open readwrite and if that failed, try readonly" code there.
> I can't really say why it's done that way: Mike?  Maybe it was a
> workaround to not having the right permissions to open that
> persistent file?

The notion was that of "best effort," and it is sloppy.

I think the right way to do it will be to allow up to two persistent
files. If the user with read-only perms opens, then open the
persistent file RO. Then a user with write-only (but not read) perms
opens; open another persistent file WO. Allow subsequent reads or
writes by the various users to go through whichever persistent file
has the right access. Then a user with RW access opens the file; close
both the RO file and the WO file and open a new file RW. All the
while, make sure that ecryptfs_open() performs all the requisite perm
checks.

If this sounds reasonable, I will get working on a patch to do this.

Mike