[PATCH net v2] tipc: protect node reset trace dump with node lock

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 (net/tipc/link.c:2910)
  Read of size 4 by task poc/115
  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 write lock around the trace event. This serializes the
dump against tipc_node_link_down(delete=true), which frees the link
under the same write lock.

Do not take the lock inside tipc_node_dump() itself: several dump
callers, including tipc_node_link_down(), already hold the write lock.

Fixes: eb18a510b5cd ("tipc: add trace_events for tipc node")
Cc: [email protected]
Signed-off-by: Chengfeng Ye <[email protected]>
---
v1 -> v2:
- Use tipc_node_write_lock() instead of tipc_node_read_lock() so the
  dump is exclusive with link deletion.

 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_write_lock(n);
 	trace_tipc_node_reset_links(n, true, " ");
+	tipc_node_write_unlock(n);
 	for (i = 0; i < MAX_BEARERS; i++) {
 		tipc_node_link_down(n, i, false);
 	}
-- 
2.43.0