From b170997acedc6c11ed2ec07b8d415601e65bb452 Mon Sep 17 00:00:00 2001 From: Jon Paul Maloy Date: Wed, 24 Feb 2016 11:00:19 -0500 Subject: [PATCH] tipc: eliminate risk of finding to-be-deleted node instance Although we have never seen it happen, we have identified the following problematic scenario when nodes are stopped and deleted: CPU0: CPU1: tipc_node_xxx() //ref == 1 tipc_node_put() //ref -> 0 tipc_node_find() // node still in table tipc_node_delete() list_del_rcu(n. list) tipc_node_get() //ref -> 1, bad kfree_rcu() tipc_node_put() //ref to 0 again. kfree_rcu() // BOOM! We fix this by introducing use of the conditional kref_get_if_not_zero() instead of kref_get() in the function tipc_node_find(). This eliminates any risk of post-mortem access. Reported-by: Zhijiang Hu Acked-by: Ying Xue Signed-off-by: Jon Maloy Signed-off-by: David S. Miller --- net/tipc/node.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/net/tipc/node.c b/net/tipc/node.c index 9fcc2fb0ee00..792bbcbb3eed 100644 --- a/net/tipc/node.c +++ b/net/tipc/node.c @@ -245,23 +245,23 @@ static void tipc_node_get(struct tipc_node *node) */ static struct tipc_node *tipc_node_find(struct net *net, u32 addr) { - struct tipc_net *tn = net_generic(net, tipc_net_id); + struct tipc_net *tn = tipc_net(net); struct tipc_node *node; + unsigned int thash = tipc_hashfn(addr); if (unlikely(!in_own_cluster_exact(net, addr))) return NULL; rcu_read_lock(); - hlist_for_each_entry_rcu(node, &tn->node_htable[tipc_hashfn(addr)], - hash) { - if (node->addr == addr) { - tipc_node_get(node); - rcu_read_unlock(); - return node; - } + hlist_for_each_entry_rcu(node, &tn->node_htable[thash], hash) { + if (node->addr != addr) + continue; + if (!kref_get_unless_zero(&node->kref)) + node = NULL; + break; } rcu_read_unlock(); - return NULL; + return node; } static void tipc_node_read_lock(struct tipc_node *n) -- 2.20.1