[PATCH net] tipc: protect node reset trace dump with node lock

[Chengfeng Ye <nicoyip.dev@gmail.com>]

The tipc_node_reset_links trace event asks tipc_node_dump() to walk the
node's link entries. Unlike the other node events that request link data,
this event runs without the node lock.

This permits bearer teardown to free a link while the trace callback is
dumping it:

  CPU 0                                CPU 1
  trace_tipc_node_reset_links()
    tipc_node_dump()
      l = n->links[0].link
                                       tipc_node_write_lock()
                                       kfree(l)
                                       n->links[0].link = NULL
                                       tipc_node_write_unlock()
      tipc_link_dump(l)

tipc_link_dump() then dereferences the stale pointer. KASAN reported:

  BUG: KASAN: slab-use-after-free in tipc_link_dump+0x10cb/0x16b0
  Read of size 4 by task ksoftirqd/0/14
  Call Trace:
   tipc_link_dump+0x10cb/0x16b0
   tipc_node_dump+0x4bb/0x740
   trace_event_raw_event_tipc_node_class+0x258/0x360
   tipc_node_reset_links+0x14d/0x1a0
   tipc_rcv+0x13f5/0x3030
   tipc_udp_recv+0x4e3/0x670
  Allocated by task 0:
   tipc_link_create+0x1e1/0x1020
   tipc_node_check_dest+0x7d2/0x11a0
   tipc_disc_rcv+0xdbf/0x1430
  Freed by task 89:
   kfree+0x131/0x3c0
   tipc_node_link_down+0x267/0x4b0
   tipc_node_delete_links+0xec/0x160
   bearer_disable+0x107/0x260

Take the node read lock around the trace event. This keeps link pointer
loads and all dump dereferences serialized against link deletion while
preserving the trace contents and reset flow.

Fixes: eb18a510b5cd ("tipc: add trace_events for tipc node")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
 net/tipc/node.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/tipc/node.c b/net/tipc/node.c
index 683a136e53ef..127848e8a644 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -1333,7 +1333,9 @@ static void tipc_node_reset_links(struct tipc_node *n)
 
 	pr_warn("Resetting all links to %x\n", n->addr);
 
+	tipc_node_read_lock(n);
 	trace_tipc_node_reset_links(n, true, " ");
+	tipc_node_read_unlock(n);
 	for (i = 0; i < MAX_BEARERS; i++) {
 		tipc_node_link_down(n, i, false);
 	}
-- 
2.43.0