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

[Tung Quang Nguyen]

>Subject: [PATCH net] tipc: fix NULL deref in tipc_named_node_up() on empty
>publication list
>
>named_distribute() builds the bulk messages for @pls into @list and then
>dereferences the tail skb:
>
>	hdr = buf_msg(skb_peek_tail(list));
>	msg_set_last_bulk(hdr);
>
>If @pls is empty no skb is enqueued, skb_peek_tail() returns NULL, and
>msg_set_last_bulk() writes through buf_msg(NULL).
>
>tipc_named_node_up() passes &nt->cluster_scope. With a node-id
>configuration the TIPC_NODE_STATE name is published by tipc_net_finalize()
>from a work item, which sets the node address before publishing the name.
>The node accepts links once the address is set, so a link that comes up before
>the publish runs named_distribute() on an empty cluster_scope:
>
> KASAN: null-ptr-deref in range [0x00000000000000d8-0x00000000000000df]
> RIP: 0010:tipc_named_node_up (net/tipc/name_distr.c:196)
>  tipc_named_node_up (net/tipc/name_distr.c:196 net/tipc/name_distr.c:221)
>  tipc_node_write_unlock (net/tipc/node.c:428)
>  tipc_rcv (net/tipc/node.c:2185)
>  tipc_udp_recv (net/tipc/udp_media.c:392)  Kernel panic - not syncing: Fatal
>exception in interrupt
>
>TIPC genl ops use GENL_UNS_ADMIN_PERM, so an unprivileged user can reach
>this from a user+net namespace.
>
>Return early from named_distribute() when the list is empty, and skip
>tipc_node_xmit() for an empty chain. The empty chain would otherwise hit
>tipc_lxc_xmit() -> buf_msg(skb_peek(list)), the same zero-skb case fixed for
>tipc_link_xmit() in commit b77413446408 ("tipc: fix NULL deref in
>tipc_link_xmit()").

It needs to return earlier in tipc_named_node_up() like this:

diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c
index ba4f4906e13b..60ccaa862162 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;
+       }
        named_distribute(net, &head, dnode, &nt->cluster_scope, seqno);
        tipc_node_xmit(net, &head, dnode, 0);
        read_unlock_bh(&nt->cluster_scope_lock);

>
>Fixes: cad2929dc432 ("tipc: update a binding service via broadcast")
>Reported-by: Xiang Mei <xmei5@xxxxxxx>
>Assisted-by: Claude:claude-opus-4-8
>Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
>---
> net/tipc/name_distr.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
>diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c index
>ba4f4906e13b..c04fea4650a5 100644
>--- a/net/tipc/name_distr.c
>+++ b/net/tipc/name_distr.c
>@@ -192,7 +192,10 @@ static void named_distribute(struct net *net, struct
>sk_buff_head *list,
> 		skb_trim(skb, INT_H_SIZE + (msg_dsz - msg_rem));
> 		__skb_queue_tail(list, skb);
> 	}
>-	hdr = buf_msg(skb_peek_tail(list));
>+	skb = skb_peek_tail(list);
>+	if (!skb)
>+		return;
>+	hdr = buf_msg(skb);
> 	msg_set_last_bulk(hdr);
> 	msg_set_named_seqno(hdr, seqno);
> }
>@@ -219,7 +222,8 @@ void tipc_named_node_up(struct net *net, u32 dnode,
>u16 capabilities)
>
> 	read_lock_bh(&nt->cluster_scope_lock);
> 	named_distribute(net, &head, dnode, &nt->cluster_scope, seqno);
>-	tipc_node_xmit(net, &head, dnode, 0);
>+	if (!skb_queue_empty(&head))
>+		tipc_node_xmit(net, &head, dnode, 0);
> 	read_unlock_bh(&nt->cluster_scope_lock);
> }
>
>--
>2.43.0
>