nfs: properly disallow delegation requests on directories

Checking for S_ISREG() in nfs4_setlease() is incorrect, since that op is
never called for directories. The right way to deny lease requests on
directories is to set the ->setlease() operation to simple_nosetlease()
in the directory file_operations.

Fixes: e6d28eb ("filelock: push the S_ISREG check down to ->setlease handlers")
Reported-by: Christoph Hellwig <hch@infradead.org>
Closes: https://lore.kernel.org/linux-fsdevel/aV316LhsVSl0n9-E@infradead.org/
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260107-setlease-6-19-v1-1-85f034abcc57@kernel.org
Tested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: jtlayton

fs/nfs/dir.c

@@ -66,6 +66,7 @@ const struct file_operations nfs_dir_operations = {
 	.open		= nfs_opendir,
 	.release	= nfs_closedir,
 	.fsync		= nfs_fsync_dir,
+	.setlease	= simple_nosetlease,
 };
 
 const struct address_space_operations nfs_dir_aops = {

fs/nfs/nfs4file.c

@@ -431,8 +431,6 @@ void nfs42_ssc_unregister_ops(void)
 static int nfs4_setlease(struct file *file, int arg, struct file_lease **lease,
 			 void **priv)
 {
-	if (!S_ISREG(file_inode(file)->i_mode))
-		return -EINVAL;
 	return nfs4_proc_setlease(file, arg, lease, priv);
 }