Re: rpcbind redux

[Patrick Goetz <pgoetz@math.utexas.edu>]

On 10/1/20 3:06 PM, J. Bruce Fields wrote:
> On Thu, Oct 01, 2020 at 01:41:39PM -0500, Patrick Goetz wrote:
>> Hi Bruce,
>>
>> Thanks for the reply. See below.
>>
>> On 10/1/20 1:30 PM, J. Bruce Fields wrote:
>>> On Fri, Sep 25, 2020 at 09:40:16AM -0500, Patrick Goetz wrote:
>>>> My University information security office does not like rpcbind and
>>>> will automatically quarantine any system for which they detect a
>>>> portmapper running on an exposed port.
>>>>
>>>> Since I exclusively use NFSv4 I was happy to "learn" that NFSv4
>>>> doesn't require rpcbind any more.  For example, here's what it says
>>>> in the current RHEL documentation:
>>>>
>>>> "NFS version 4 (NFSv4) works through firewalls and on the Internet,
>>>> no longer requires an rpcbind service, supports Access Control Lists
>>>> (ACLs), and utilizes stateful operations."
>>>>
>>>> https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/managing_file_systems/exporting-nfs-shares_managing-file-systems#introduction-to-nfs_exporting-nfs-shares
>>>>
>>>> I'm using Ubuntu 20.04 rather than RHEL, but the nfs-server service
>>>> absolutely will not start if it can't launch rpcbind as a precursor:
>>>>
>>>> -----------------------------
>>>> root@helios:~# systemctl stop rpcbind
>>>> Warning: Stopping rpcbind.service, but it can still be activated by:
>>>>    rpcbind.socket
>>>> root@helios:~# systemctl mask rpcbind
>>>> Created symlink /etc/systemd/system/rpcbind.service → /dev/null.
>>>>
>>>> root@helios:~# systemctl restart nfs-server
>>>> Job for nfs-server.service canceled.
>>>> root@helios:~# systemctl status nfs-server
>>>> ● nfs-server.service - NFS server and services
>>>>       Loaded: loaded (/lib/systemd/system/nfs-server.service;
>>>> enabled; vendor preset: enabled)
>>>>      Drop-In: /run/systemd/generator/nfs-server.service.d
>>>>               └─order-with-mounts.conf
>>>>       Active: failed (Result: exit-code) since Fri 2020-09-25
>>>> 14:21:46 UTC; 10s ago
>>>>      Process: 3923 ExecStartPre=/usr/sbin/exportfs -r (code=exited,
>>>> status=0/SUCCESS)
>>>>      Process: 3925 ExecStart=/usr/sbin/rpc.nfsd $RPCNFSDARGS
>>>> (code=exited, status=1/FAILURE)
>>>>      Process: 3931 ExecStopPost=/usr/sbin/exportfs -au (code=exited,
>>>> status=0/SUCCESS)
>>>>      Process: 3932 ExecStopPost=/usr/sbin/exportfs -f (code=exited,
>>>> status=0/SUCCESS)
>>>>     Main PID: 3925 (code=exited, status=1/FAILURE)
>>>>
>>>> Sep 25 14:21:46 helios systemd[1]: Starting NFS server and services...
>>>> Sep 25 14:21:46 helios rpc.nfsd[3925]: rpc.nfsd: writing fd to
>>>> kernel failed: errno 111 (Connection refused)
>>>> Sep 25 14:21:46 helios rpc.nfsd[3925]: rpc.nfsd: unable to set any
>>>> sockets for nfsd
>>>> Sep 25 14:21:46 helios systemd[1]: nfs-server.service: Main process
>>>> exited, code=exited, status=1/FAILURE
>>>> Sep 25 14:21:46 helios systemd[1]: nfs-server.service: Failed with
>>>> result 'exit-code'.
>>>> Sep 25 14:21:46 helios systemd[1]: Stopped NFS server and services.
>>>> -----------------------------
>>>>
>>>> So, now I'm confused.  Does NFSv4 need rpcbind to be running, does
>>>> it just need it when it launches, or something else?  I made a local
>>>> copy of the systemd service file and edited out the rpcbind
>>>> dependency, so it's not that.
>>>
>>> Do you have v2 and v3 turned off in /etc/nfs.conf?
>>
>> It's an Ubuntu system, hence doesn't use /etc/nfs.conf; however I do
>> have these variables set in /etc/default/nfs-kernel-server :
>>
>>    MOUNTD_NFS_V2="no"
>>    MOUNTD_NFS_V3="no"
>>    RPCMOUNTDOPTS="--manage-gids -N 2 -N 3"
>>
>> maybe this isn't the correct way to disable NFSv2/3, but it's all I
>> could find documented.
> 
> That should do it, but if you want to verify that it worked, you can
> read /proc/fs/nfsd/versions.

That's it.  The syntax above is *not* disabling NFSv3:

root@helios:~# cat /proc/fs/nfsd/versions
-2 +3 +4 +4.1 +4.2



> 
>> The linux kernel version is 5.4.0, and the nfs-kernel-server package
>> version is 1:1.3.4-2.5ubuntu3.3 (so upstream 1.3.4), but I'm not
>> sure this is relevant.
> 
> I can't reproduce the problem on my 5.9-ish server, but I also can't
> recall any relevant changes here.
> 
> Looking back through the history....  Kinglong Mee fixed the server to
> ignore rpbind failures in the v4-only case about 7 years ago, back in
> 4.13.
> 
> --b.
>