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Date:   Wed, 15 May 2019 10:01:12 -0400
To:     Trond Myklebust <trondmy@gmail.com>
Cc:     steved@redhat.com, linux-nfs@vger.kernel.org
Subject: Re: [RFC PATCH 0/5] Add a chroot option to nfs.conf
Message-ID: <20190515140112.GA9291@fieldses.org>
References: <20190514204153.79603-1-trond.myklebust@hammerspace.com>
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From:   bfields@fieldses.org (J. Bruce Fields)
Sender: linux-nfs-owner@vger.kernel.org
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On Tue, May 14, 2019 at 04:41:48PM -0400, Trond Myklebust wrote:
> The following patchset aims to allow the configuration of a 'chroot
> jail' to rpc.nfsd, and allowing us to export a filesystem /foo (and
> possibly subtrees) as '/'.

This is great, thanks!  Years ago I did an incomplete version that
worked by just string manipulations on paths.  Running part of mountd in
a chrooted thread is a neat way to do it.

If I understand right, the only part that's being run in a chroot is the
writes to /proc/net/sunrpc/*/channel files.  So that means that the path
included in writes to /proc/net/sunrpc/nfsd_fh/channel will be resolved
with respect to the chroot by the kernel code handling the write.

That's not the only place in mountd that uses export paths, though.
What about:

	- next_mnt(), which compares paths from the export file to paths
	  in /etc/mtab.
	- is_mountpoint, which stats export paths.
	- match_fsid, which stats export paths.

Etc.  Doesn't that stuff also need to be done with respect to the
chroot?  Am I missing something?

--b.

> 
> Trond Myklebust (5):
>   mountd: Ensure we don't share cache file descriptors among processes.
>   Add a simple workqueue mechanism
>   Add a helper to write to a file through the chrooted thread
>   Add support for chrooted exports
>   Add support for chroot in exportfs
> 
>  aclocal/libpthread.m4      |  13 +-
>  configure.ac               |   6 +-
>  nfs.conf                   |   1 +
>  support/include/misc.h     |  11 ++
>  support/misc/Makefile.am   |   2 +-
>  support/misc/workqueue.c   | 267 +++++++++++++++++++++++++++++++++++++
>  systemd/nfs.conf.man       |   3 +-
>  utils/exportfs/Makefile.am |   2 +-
>  utils/exportfs/exportfs.c  |  31 ++++-
>  utils/mountd/Makefile.am   |   3 +-
>  utils/mountd/cache.c       |  39 +++++-
>  utils/mountd/mountd.c      |   5 +-
>  utils/nfsd/nfsd.man        |   4 +
>  13 files changed, 369 insertions(+), 18 deletions(-)
>  create mode 100644 support/misc/workqueue.c
> 
> -- 
> 2.21.0