Re: [PATCH net v2] tipc: fix NULL deref in tipc_named_node_up() on empty publication list

[Simon Horman <horms@kernel.org>]

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---
tipc: fix NULL deref in tipc_named_node_up() on empty publication list

This commit fixes a NULL pointer dereference in tipc_named_node_up() that
occurs when the cluster_scope publication list is empty. The fix introduces
an early return to avoid calling named_distribute() with an empty list.

> diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c
> index ba4f4906e13b7..60ccaa862162c 100644
> --- a/net/tipc/name_distr.c
> +++ b/net/tipc/name_distr.c
> @@ -218,6 +218,10 @@ void tipc_named_node_up(struct net *net, u32 dnode, u16 capabilities)
>  	spin_unlock_bh(&tn->nametbl_lock);
>  
>  	read_lock_bh(&nt->cluster_scope_lock);
> +	if (list_empty(&nt->cluster_scope)) {
> +		read_unlock_bh(&nt->cluster_scope_lock);
> +		return;
> +	}

[Severity: Critical]
Does this early return prevent the transmission of the last_bulk
synchronization message to the peer node?

In tipc_named_dequeue(), the peer node sets *open = true only when receiving
a message where msg_is_last_bulk(hdr) is true:

net/tipc/name_distr.c:tipc_named_dequeue() {
        ...
        if (*open && (*rcv_nxt == seqno)) {
                (*rcv_nxt)++;
                __skb_unlink(skb, namedq);
                ...
                return skb;
        }
        ...
}

If *open is false, all subsequent non-bulk name publications will fail this
sequence check and remain in the namedq indefinitely. 

Without sending the last_bulk message, could this cause a permanent stall
of name table updates and an unbounded memory leak of socket buffers on the
peer node?

>  	named_distribute(net, &head, dnode, &nt->cluster_scope, seqno);

[Severity: High]
This isn't a bug introduced by this patch, but looking at named_distribute()
called here, what happens if buffer allocation fails during the loop?

Inside named_distribute():

net/tipc/name_distr.c:named_distribute() {
        ...
        if (!skb) {
                skb = named_prepare_buf(net, PUBLICATION, msg_rem, dnode);
                if (!skb) {
                        pr_warn("Bulk publication failure\n");
                        return;
                }
        ...
}

If the function returns early due to allocation failure, the messages
already added to the queue are transmitted by tipc_node_xmit(), but none
of them will have the last_bulk flag set since that happens at the very end
of the function.

Could this also prevent the receiving node from transitioning its named_open
state to true, leading to the exact same permanent stall and memory leak of
subsequent normal name publications?

>  	tipc_node_xmit(net, &head, dnode, 0);
>  	read_unlock_bh(&nt->cluster_scope_lock);
-- 
pw-bot: changes-requested