ocfs2: Fix use of slab data with sendpage

ocfs2 uses kzalloc() to allocate buffers for o2net_hand, o2net_keep_req and
o2net_keep_resp and then passes these to sendpage.  This isn't really
allowed as the lifetime of slab objects is not controlled by page ref -
though in this case it will probably work.  sendmsg() with MSG_SPLICE_PAGES
will, however, print a warning and give an error.

Fix it to use folio_alloc() instead to allocate a buffer for the handshake
message, keepalive request and reply messages.

Fixes: 9821148 ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Mark Fasheh <mark@fasheh.com>
cc: Kurt Hackel <kurt.hackel@oracle.com>
cc: Joel Becker <jlbec@evilplan.org>
cc: Joseph Qi <joseph.qi@linux.alibaba.com>
cc: ocfs2-devel@oss.oracle.com
Link: https://lore.kernel.org/r/20230623225513.2732256-14-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

fs/ocfs2/cluster/tcp.c

@@ -2087,18 +2087,24 @@ void o2net_stop_listening(struct o2nm_node *node)
 
 int o2net_init(void)
 {
+	struct folio *folio;
+	void *p;
 	unsigned long i;
 
 	o2quo_init();
-
 	o2net_debugfs_init();
 
-	o2net_hand = kzalloc(sizeof(struct o2net_handshake), GFP_KERNEL);
-	o2net_keep_req = kzalloc(sizeof(struct o2net_msg), GFP_KERNEL);
-	o2net_keep_resp = kzalloc(sizeof(struct o2net_msg), GFP_KERNEL);
-	if (!o2net_hand || !o2net_keep_req || !o2net_keep_resp)
+	folio = folio_alloc(GFP_KERNEL | __GFP_ZERO, 0);
+	if (!folio)
 		goto out;
 
+	p = folio_address(folio);
+	o2net_hand = p;
+	p += sizeof(struct o2net_handshake);
+	o2net_keep_req = p;
+	p += sizeof(struct o2net_msg);
+	o2net_keep_resp = p;
+
 	o2net_hand->protocol_version = cpu_to_be64(O2NET_PROTOCOL_VERSION);
 	o2net_hand->connector_id = cpu_to_be64(1);
 
@@ -2124,9 +2130,6 @@ int o2net_init(void)
 	return 0;
 
 out:
-	kfree(o2net_hand);
-	kfree(o2net_keep_req);
-	kfree(o2net_keep_resp);
 	o2net_debugfs_exit();
 	o2quo_exit();
 	return -ENOMEM;
@@ -2135,8 +2138,6 @@ int o2net_init(void)
 void o2net_exit(void)
 {
 	o2quo_exit();
-	kfree(o2net_hand);
-	kfree(o2net_keep_req);
-	kfree(o2net_keep_resp);
 	o2net_debugfs_exit();
+	folio_put(virt_to_folio(o2net_hand));
 }