Re: [net] tipc: fix NULL pointer dereference in tipc_named_rcv

[Jon Maloy]

On 10/8/20 1:25 PM, Jakub Kicinski wrote:
On Thu,  8 Oct 2020 14:31:56 +0700 Hoang Huu Le wrote:
diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c
index 2f9c148f17e2..fe4edce459ad 100644
--- a/net/tipc/name_distr.c
+++ b/net/tipc/name_distr.c
@@ -327,8 +327,13 @@ static struct sk_buff *tipc_named_dequeue(struct 
sk_buff_head *namedq,
        struct tipc_msg *hdr;
        u16 seqno;
  
+	spin_lock_bh(&namedq->lock);
        skb_queue_walk_safe(namedq, skb, tmp) {
-               skb_linearize(skb);
+               if (unlikely(skb_linearize(skb))) {
+                       __skb_unlink(skb, namedq);
+                       kfree_skb(skb);
+                       continue;
+               }
                hdr = buf_msg(skb);
                seqno = msg_named_seqno(hdr);
                if (msg_is_last_bulk(hdr)) {
@@ -338,12 +343,14 @@ static struct sk_buff *tipc_named_dequeue(struct 
sk_buff_head *namedq,
  
  		if (msg_is_bulk(hdr) || msg_is_legacy(hdr)) {
                        __skb_unlink(skb, namedq);
+                       spin_unlock_bh(&namedq->lock);
                        return skb;
                }
  
  		if (*open && (*rcv_nxt == seqno)) {
                        (*rcv_nxt)++;
                        __skb_unlink(skb, namedq);
+                       spin_unlock_bh(&namedq->lock);
                        return skb;
                }
  
@@ -353,6 +360,7 @@ static struct sk_buff *tipc_named_dequeue(struct sk_buff_head *namedq,
                        continue;
                }
        }
+       spin_unlock_bh(&namedq->lock);
        return NULL;
  }
  
diff --git a/net/tipc/node.c b/net/tipc/node.c
index cf4b239fc569..d269ebe382e1 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -1496,7 +1496,7 @@ static void node_lost_contact(struct tipc_node *n,
  
  	/* Clean up broadcast state */
        tipc_bcast_remove_peer(n->net, n->bc_entry.link);
-       __skb_queue_purge(&n->bc_entry.namedq);
+       skb_queue_purge(&n->bc_entry.namedq);
Patch looks fine, but I'm not sure why not hold
spin_unlock_bh(&tn->nametbl_lock) here instead?

Seems like node_lost_contact() should be relatively rare,
so adding another lock to tipc_named_dequeue() is not the
right trade off.
Actually, I agree with previous speaker here. We already have the 
nametbl_lock when tipc_named_dequeue() is called, and the same lock is 
accessible from no.c where node_lost_contact() is executed. The patch 
and the code becomes simpler.
I suggest you post a v2 of this one.

///jon

        /* Abort any ongoing link failover */
        for (i = 0; i < MAX_BEARERS; i++) {