From 794ed393b707f01858f5ebe2ae5eabaf89d00022 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 25 Jan 2013 07:44:41 +0000 Subject: [PATCH] net: loopback: fix a dst refcounting issue Ben Greear reported crashes in ip_rcv_finish() on a stress test involving many macvlans. We tracked the bug to a dst use after free. ip_rcv_finish() was calling dst->input() and got garbage for dst->input value. It appears the bug is in loopback driver, lacking a skb_dst_force() before calling netif_rx(). As a result, a non refcounted dst, normally protected by a RCU read_lock section, was escaping this section and could be freed before the packet being processed. [] loopback_xmit+0x64/0x83 [] dev_hard_start_xmit+0x26c/0x35e [] dev_queue_xmit+0x2c4/0x37c [] ? dev_hard_start_xmit+0x35e/0x35e [] ? eth_header+0x28/0xb6 [] neigh_resolve_output+0x176/0x1a7 [] ip_finish_output2+0x297/0x30d [] ? ip_finish_output2+0x137/0x30d [] ip_finish_output+0x63/0x68 [] ip_output+0x61/0x67 [] dst_output+0x17/0x1b [] ip_local_out+0x1e/0x23 [] ip_queue_xmit+0x315/0x353 [] ? ip_send_unicast_reply+0x2cc/0x2cc [] tcp_transmit_skb+0x7ca/0x80b [] tcp_connect+0x53c/0x587 [] ? getnstimeofday+0x44/0x7d [] ? ktime_get_real+0x11/0x3e [] tcp_v4_connect+0x3c2/0x431 [] __inet_stream_connect+0x84/0x287 [] ? inet_stream_connect+0x22/0x49 [] ? _local_bh_enable_ip+0x84/0x9f [] ? local_bh_enable+0xd/0x11 [] ? lock_sock_nested+0x6e/0x79 [] ? inet_stream_connect+0x22/0x49 [] inet_stream_connect+0x33/0x49 [] sys_connect+0x75/0x98 This bug was introduced in linux-2.6.35, in commit 7fee226ad2397b (net: add a noref bit on skb dst) skb_dst_force() is enforced in dev_queue_xmit() for devices having a qdisc. Reported-by: Ben Greear Signed-off-by: Eric Dumazet Tested-by: Ben Greear Signed-off-by: David S. Miller --- drivers/net/loopback.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c index 81f8f9e31db5..fcbf680c3e62 100644 --- a/drivers/net/loopback.c +++ b/drivers/net/loopback.c @@ -77,6 +77,11 @@ static netdev_tx_t loopback_xmit(struct sk_buff *skb, skb_orphan(skb); + /* Before queueing this packet to netif_rx(), + * make sure dst is refcounted. + */ + skb_dst_force(skb); + skb->protocol = eth_type_trans(skb, dev); /* it's OK to use per_cpu_ptr() because BHs are off */ -- 2.34.1