Re: [PATCH] ipv4: fib: avoid NULL dereference

On Fri, Jul 06, 2018 at 08:49:14AM -0600, David Ahern wrote:

On 7/6/18 8:28 AM, Mark Rutland wrote:

quoted

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 5bc0c89e81e4..8d98c8162554 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c

@@ -497,11 +497,11 @@ static void tnode_free(struct key_vector *tn)
 	struct callback_head *head = &tn_info(tn)->rcu;
 
 	while (head) {
+		tn = container_of(head, struct tnode, rcu)->kv;
+
 		head = head->next;
 		tnode_free_size += TNODE_SIZE(1ul << tn->bits);
 		node_free(tn);

you are changing tn before the above 2 calls are made on the tn passed in

As tn_info(tn) is container_of(kv, struct tnode, tn), the end result is
the same tn value, so this is not a problem.

Thanks,
Mark.