Re: [PATCH 0/5] nfs: Fix mounting NFS3 AUTH_NULL exports

[Anna Schumaker]

Hi Pali,

On 9/12/24 9:02 AM, Pali Rohár wrote:
> Linux NFS3 kernel client currently has broken support for NFS3
> AUTH_NULL-only exports and also broken mount option -o sec=none
> (which explicitly specifies that mount should use AUTH_NULL).
> 
> For AUTH_NULL-only server exports, Linux NFS3 kernel client mounts such
> export with AUTH_UNIX authentication which results in unusable mount
> point (any operation on it fails with error because server rejects
> AUTH_UNIX authentication).
> 
> Half of the problem is with MNTv3 servers, as some of them (e.g. Linux
> one) never announce AUTH_NULL authentication for any export. Linux MNTv3
> server does not announce it even when the export has the only AUTH_NULL
> auth method allowed, instead it announce AUTH_UNIX (even when AUTH_UNIX
> is disabled for that export in Linux NFS3 knfsd server). So MNTv3 server
> for AUTH_NONE-only exports instruct Linux NFS3 kernel client to use
> AUTH_UNIX and then NFS3 server refuse access to files with AUTH_UNIX.
> 
> Main problem on the client side is that mount option -o sec=none for
> NFS3 client is not processed and Linux NFS kernel client always skips
> AUTH_NULL (even when server announce it, and also even when user
> specifies -o sec=none on mount command line).
> 
> This patch series address these issues in NFS3 client code.
> 
> Add a workaround for buggy MNTv3 servers which do not announce AUTH_NULL,
> by trying AUTH_NULL authentication as an absolutely last chance when
> everything else fails. And honors user choice of AUTH_NULL if user
> explicitly specified -o sec=none as mount option.

Why fix this on the client instead of fixing the server to announce AUTH_NULL
if this is what the user has configured?

Anna

> 
> AUTH_NULL authentication is useful for read-only exports, including
> public exports. As authentication for these types of exports do not have
> to be required.
> 
> Patch series was tested with AUTH_NULL-only, AUTH_UNIX-only and combined
> AUTH_NULL+AUTH_UNIX exports from Linux knfsd NFS3 server + default Linux
> MNTv3 userspace server. And also tested with exports from modified MNTv3
> server to properly return AUTH_NULL support in response list.
> 
> Patch series is based on the latest upstream tag v6.11-rc7.
> 
> Pali Rohár (5):
>   nfs: Fix support for NFS3 mount with -o sec=none from Linux MNTv3
>     server
>   nfs: Propagate AUTH_NULL/AUTH_UNIX PATHCONF NFS3ERR_ACCESS failures
>   nfs: Try to use AUTH_NULL for NFS3 mount when no -o sec was given
>   nfs: Fix -o sec=none output in /proc/mounts
>   nfs: Remove duplicate debug message 'using auth flavor'
> 
>  fs/nfs/client.c | 14 ++++++++++-
>  fs/nfs/super.c  | 64 +++++++++++++++++++++++++++++++++++++++----------
>  2 files changed, 65 insertions(+), 13 deletions(-)
>