[PATCH 5.15 50/98] tipc: move bc link creation back to tipc_node_create

[Greg Kroah-Hartman]

From: Xin Long <lucien.xin@xxxxxxxxx>

commit cb8092d70a6f5f01ec1490fce4d35efed3ed996c upstream.

Shuang Li reported a NULL pointer dereference crash:

  [] BUG: kernel NULL pointer dereference, address: 0000000000000068
  [] RIP: 0010:tipc_link_is_up+0x5/0x10 [tipc]
  [] Call Trace:
  []  <IRQ>
  []  tipc_bcast_rcv+0xa2/0x190 [tipc]
  []  tipc_node_bc_rcv+0x8b/0x200 [tipc]
  []  tipc_rcv+0x3af/0x5b0 [tipc]
  []  tipc_udp_recv+0xc7/0x1e0 [tipc]

It was caused by the 'l' passed into tipc_bcast_rcv() is NULL. When it
creates a node in tipc_node_check_dest(), after inserting the new node
into hashtable in tipc_node_create(), it creates the bc link. However,
there is a gap between this insert and bc link creation, a bc packet
may come in and get the node from the hashtable then try to dereference
its bc link, which is NULL.

This patch is to fix it by moving the bc link creation before inserting
into the hashtable.

Note that for a preliminary node becoming "real", the bc link creation
should also be called before it's rehashed, as we don't create it for
preliminary nodes.

Fixes: 4cbf8ac2fe5a ("tipc: enable creating a "preliminary" node")
Reported-by: Shuang Li <shuali@xxxxxxxxxx>
Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Acked-by: Jon Maloy <jmaloy@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/tipc/node.c |   41 ++++++++++++++++++++++-------------------
 1 file changed, 22 insertions(+), 19 deletions(-)

--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -472,8 +472,8 @@ struct tipc_node *tipc_node_create(struc
 				   bool preliminary)
 {
 	struct tipc_net *tn = net_generic(net, tipc_net_id);
+	struct tipc_link *l, *snd_l = tipc_bc_sndlink(net);
 	struct tipc_node *n, *temp_node;
-	struct tipc_link *l;
 	unsigned long intv;
 	int bearer_id;
 	int i;
@@ -488,6 +488,16 @@ struct tipc_node *tipc_node_create(struc
 			goto exit;
 		/* A preliminary node becomes "real" now, refresh its data */
 		tipc_node_write_lock(n);
+		if (!tipc_link_bc_create(net, tipc_own_addr(net), addr, peer_id, U16_MAX,
+					 tipc_link_min_win(snd_l), tipc_link_max_win(snd_l),
+					 n->capabilities, &n->bc_entry.inputq1,
+					 &n->bc_entry.namedq, snd_l, &n->bc_entry.link)) {
+			pr_warn("Broadcast rcv link refresh failed, no memory\n");
+			tipc_node_write_unlock_fast(n);
+			tipc_node_put(n);
+			n = NULL;
+			goto exit;
+		}
 		n->preliminary = false;
 		n->addr = addr;
 		hlist_del_rcu(&n->hash);
@@ -567,7 +577,16 @@ update:
 	n->signature = INVALID_NODE_SIG;
 	n->active_links[0] = INVALID_BEARER_ID;
 	n->active_links[1] = INVALID_BEARER_ID;
-	n->bc_entry.link = NULL;
+	if (!preliminary &&
+	    !tipc_link_bc_create(net, tipc_own_addr(net), addr, peer_id, U16_MAX,
+				 tipc_link_min_win(snd_l), tipc_link_max_win(snd_l),
+				 n->capabilities, &n->bc_entry.inputq1,
+				 &n->bc_entry.namedq, snd_l, &n->bc_entry.link)) {
+		pr_warn("Broadcast rcv link creation failed, no memory\n");
+		kfree(n);
+		n = NULL;
+		goto exit;
+	}
 	tipc_node_get(n);
 	timer_setup(&n->timer, tipc_node_timeout, 0);
 	/* Start a slow timer anyway, crypto needs it */
@@ -1155,7 +1174,7 @@ void tipc_node_check_dest(struct net *ne
 			  bool *respond, bool *dupl_addr)
 {
 	struct tipc_node *n;
-	struct tipc_link *l, *snd_l;
+	struct tipc_link *l;
 	struct tipc_link_entry *le;
 	bool addr_match = false;
 	bool sign_match = false;
@@ -1175,22 +1194,6 @@ void tipc_node_check_dest(struct net *ne
 		return;
 
 	tipc_node_write_lock(n);
-	if (unlikely(!n->bc_entry.link)) {
-		snd_l = tipc_bc_sndlink(net);
-		if (!tipc_link_bc_create(net, tipc_own_addr(net),
-					 addr, peer_id, U16_MAX,
-					 tipc_link_min_win(snd_l),
-					 tipc_link_max_win(snd_l),
-					 n->capabilities,
-					 &n->bc_entry.inputq1,
-					 &n->bc_entry.namedq, snd_l,
-					 &n->bc_entry.link)) {
-			pr_warn("Broadcast rcv link creation failed, no mem\n");
-			tipc_node_write_unlock_fast(n);
-			tipc_node_put(n);
-			return;
-		}
-	}
 
 	le = &n->links[b->identity];