On Fri, Jan 14, 2022 at 12:36:23PM +0000, Chris Chilvers wrote:
> I was testing using the rootdir setting in nfs.config to allow using export
> paths that would normally conflict with local systems directories with NFS v3.
>
> The idea was to support re-exporting a source NFS server such as NetApp that
> might exports arbitrary paths such as /home without overwriting the /home
> directory on the NFS server, and even support exporting a root directory similar
> to NFS v4.
>
> While testing I ran into an issue where the NFS server would fail to start.
> During start up, the NFS server would log the error:
>
> $ systemctl status nfs-server.service
> systemd[1]: Starting NFS server and services...
> exportfs[2307]: exportfs: Failed to stat /srv/nfs/usr/bin: No such
> file or directory
> systemd[1]: nfs-server.service: Control process exited, code=exited,
> status=1/FAILURE
>
> $ cat nfs.config
> [exports]
> rootdir=/srv/nfs
>
> $ cat /etc/exports
> / 10.0.0.0/8(rw,sync,wdelay,no_root_squash,no_all_squash,no_subtree_check,sec=sys,secure,fsid=0,nohide)
> /assets 10.0.0.0/8(rw,sync,wdelay,no_root_squash,no_all_squash,no_subtree_check,sec=sys,secure,fsid=10,nohide)
> /bin 10.0.0.0/8(rw,sync,wdelay,no_root_squash,no_all_squash,no_subtree_check,sec=sys,secure,fsid=30,nohide)
> /software 10.0.0.0/8(rw,sync,wdelay,no_root_squash,no_all_squash,no_subtree_check,sec=sys,secure,fsid=40,nohide)
>
> If I create the directory /srv/nfs/usr/bin then the NFS server will start.
> Listing the actual exports shows that a different path was exported compared to
> the path from /etc/exports.
>
> $ exportfs -s
> / 10.0.0.0/8(sync,wdelay,nohide,no_subtree_check,fsid=0,sec=sys,rw,secure,no_root_squash,no_all_squ>
> /assets 10.0.0.0/8(sync,wdelay,nohide,no_subtree_check,fsid=10,sec=sys,rw,secure,no_root_squash,no_>
> /usr/bin 10.0.0.0/8(sync,wdelay,nohide,no_subtree_check,fsid=30,sec=sys,rw,secure,no_root_squash,no>
> /software 10.0.0.0/8(sync,wdelay,nohide,no_subtree_check,fsid=40,sec=sys,rw,secure,no_root_squash,n>
>
> To test this further I create a symlink from /software to /usr/lib. Once again
> the server failed to start because it could not find /srv/nfs/usr/lib.
I'm probably just reading too quickly, but I'm not seeing how this
explains the problems with your original configuration.
Is it that /sr/nfs/bin on you system is a symlink? (And what exactly is
the content of that symlink?)
(Also, for what it's worth, we don't recommend using fsid=0 any more.
It should be unnecessary.)
--b.
>
> Reading through the source, I think the issue is in the getexportent function in
> support/nfs/exports.c.
>
> /* resolve symlinks */
> if (realpath(ee.e_path, rpath) != NULL) {
> rpath[sizeof (rpath) - 1] = '\0';
> strncpy(ee.e_path, rpath, sizeof (ee.e_path) - 1);
> ee.e_path[sizeof (ee.e_path) - 1] = '\0';
> }
>
> It appears this function does not take into account the rootdir property when
> resolving e_path.
>
> This was tested on Ubuntu 20.04 with the 5.11.8-051108-generic kernel. nfs-utils
> version is 2.5.3.
