Re: [PATCH] fix NFSv4 acl detection on F39

[Trond Myklebust]

On Mon, 2023-05-15 at 13:49 -0400, Jeff Layton wrote:
> On Mon, 2023-05-15 at 17:28 +0000, Trond Myklebust wrote:
> > On Mon, 2023-05-15 at 13:11 -0400, Jeff Layton wrote:
> > > On Mon, 2023-05-15 at 11:50 +0000, Ondrej Valousek wrote:
> > > > Hi Paul,
> > > > 
> > > > Ok first of all, thanks for taking initiative on this, I am
> > > > unable
> > > > to proceed on this on my own at the moment.
> > > > I see few problems with this:
> > > > 
> > > > 1. The calculation of the 'listbufsize' is incorrect in your
> > > > patch.
> > > > It will _not_work as you expected and won't limit the number of
> > > > syscalls (which is why we came up with this patch, right?).
> > > > Check
> > > > with my original proposal, we really need to check for
> > > > 'system.nfs4' xattr name presence here
> > > > 2. It mistakenly detects an ACL presence on files which do not
> > > > have
> > > > any ACL on NFSv4 filesystem. Digging further it seems that
> > > > kernel
> > > > in F39 behaves differently to the previous kernels:
> > > > 
> > > > F38: 
> > > > # getfattr -m . /path_to_nfs4_file
> > > > # file: path_to_nfs4_file
> > > > system.nfs4_acl                                    <---- only
> > > > single xattr detected
> > > > 
> > > > F39:
> > > > # getfattr -m . /path_to_nfs4_file
> > > > # file: path_to_nfs4_file
> > > > system.nfs4_acl
> > > > system.posix_acl_default
> > > > /* SOMETIMES even shows this */
> > > > system.posix_acl_default
> > > 
> > > (cc'ing Christian and relevant kernel lists)
> > > 
> > > I assume the F39 kernel is v6.4-rc based? If so, then I think
> > > that's
> > > a
> > > regression. NFSv4 client inodes should _not_ report a POSIX ACL
> > > attribute since the protocol doesn't support them.
> > > 
> > > In fact, I think the rationale in the kernel commit below is
> > > wrong.
> > > NFSv4 has a listxattr operation, but doesn't support POSIX ACLs.
> > > 
> > > Christian, do we need to revert this?
> > > 
> > > commit e499214ce3ef50c50522719e753a1ffc928c2ec1
> > > Author: Christian Brauner <brauner@kernel.org>
> > > Date:   Wed Feb 1 14:15:01 2023 +0100
> > > 
> > >     acl: don't depend on IOP_XATTR
> > >     
> > > 
> > 
> > 
> > No. The problem is commit f2620f166e2a ("xattr: simplify listxattr
> > helpers") which helpfully inserts posix acl handlers into
> > generic_listxattr(), and makes it impossible to call from
> > nfs4_listxattr().
> > 
> 
> 
> Ahh ok. Looking at that function though, it seems like it'd only
> report
> these for mounts that set SB_POSIXACL. Any reason that we have that
> turned on with v4 mounts?
> 

So, while it may seem reasonable to assume that SB_POSIXACL means
'supports posix ACLs', that doesn't actually match the definition in
include/linux/fs.h (or the equivalent definition for MS_POSIXACL):

#define SB_POSIXACL     (1<<16) /* VFS does not apply the umask */

See the use of mode_strip_umask() in vfs_prepare_mode().

So yes, NFSv4 sets SB_POSIXACL, and it has done so since commit
a8a5da996df7 ("nfs: Set MS_POSIXACL always") because we require the VFS
to not apply the umask. 

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com