From: "J. Bruce Fields" <bfields@redhat.com>
Date: Thu, 28 Jan 2021 17:36:38 -0500
Subject: [PATCH] nfs: we don't support removing system.nfs4_acl
Git-commit: 4f8be1f53bf615102d103c0509ffa9596f65b718
Patch-mainline: v5.12
References: git-fixes

The NFSv4 protocol doesn't have any notion of reomoving an attribute, so
removexattr(path,"system.nfs4_acl") doesn't make sense.

There's no documented return value.  Arguably it could be EOPNOTSUPP but
I'm a little worried an application might take that to mean that we
don't support ACLs or xattrs.  How about EINVAL?

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfs/nfs4proc.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -5378,6 +5378,9 @@ static int __nfs4_proc_set_acl(struct in
 	unsigned int npages = DIV_ROUND_UP(buflen, PAGE_SIZE);
 	int ret, i;
 
+	/* You can't remove system.nfs4_acl: */
+	if (buflen == 0)
+		return -EINVAL;
 	if (!nfs4_server_supports_acls(server))
 		return -EOPNOTSUPP;
 	if (npages > ARRAY_SIZE(pages))