[PATCH] xattr: fix EOPNOTSUPP if fs and security xattrs disabled

[Gao Xiang <hsiangkao@redhat.com>]

commit f549d6c18c0e ("[PATCH] Generic VFS fallback for security xattrs")
introduces a behavior change of listxattr path therefore listxattr(2)
won't report EOPNOTSUPP correctly if fs and security xattrs disabled.
However it was clearly recorded in manpage all the time.

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Chengguang Xu <cgxu519@mykernel.net>
Cc: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---

Noticed when reviewing Chengguang's patch for erofs [1] (together
with ext2, f2fs). I'm not sure if it's the best approach but it
seems that security_inode_listsecurity() has other users and it
mainly focus on reporting these security xattrs...

[1] https://lore.kernel.org/r/20200526090343.22794-1-cgxu519@mykernel.net

Thanks,
Gao Xiang

 fs/xattr.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index 91608d9bfc6a..f339a67db521 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -352,13 +352,15 @@ vfs_listxattr(struct dentry *dentry, char *list, size_t size)
 	error = security_inode_listxattr(dentry);
 	if (error)
 		return error;
-	if (inode->i_op->listxattr && (inode->i_opflags & IOP_XATTR)) {
-		error = inode->i_op->listxattr(dentry, list, size);
-	} else {
-		error = security_inode_listsecurity(inode, list, size);
-		if (size && error > size)
-			error = -ERANGE;
-	}
+
+	if (inode->i_op->listxattr && (inode->i_opflags & IOP_XATTR))
+		return inode->i_op->listxattr(dentry, list, size);
+
+	if (!IS_ENABLED(CONFIG_SECURITY))
+		return -EOPNOTSUPP;
+	error = security_inode_listsecurity(inode, list, size);
+	if (size && error > size)
+		error = -ERANGE;
 	return error;
 }
 EXPORT_SYMBOL_GPL(vfs_listxattr);
-- 
2.24.0