Commits
Eric Dumazet committed 794ed393b70
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. [<ffffffff813a3c4d>] loopback_xmit+0x64/0x83 [<ffffffff81477364>] dev_hard_start_xmit+0x26c/0x35e [<ffffffff8147771a>] dev_queue_xmit+0x2c4/0x37c [<ffffffff81477456>] ? dev_hard_start_xmit+0x35e/0x35e [<ffffffff8148cfa6>] ? eth_header+0x28/0xb6 [<ffffffff81480f09>] neigh_resolve_output+0x176/0x1a7 [<ffffffff814ad835>] ip_finish_output2+0x297/0x30d [<ffffffff814ad6d5>] ? ip_finish_output2+0x137/0x30d [<ffffffff814ad90e>] ip_finish_output+0x63/0x68 [<ffffffff814ae412>] ip_output+0x61/0x67 [<ffffffff814ab904>] dst_output+0x17/0x1b [<ffffffff814adb6d>] ip_local_out+0x1e/0x23 [<ffffffff814ae1c4>] ip_queue_xmit+0x315/0x353 [<ffffffff814adeaf>] ? ip_send_unicast_reply+0x2cc/0x2cc [<ffffffff814c018f>] tcp_transmit_skb+0x7ca/0x80b [<ffffffff814c3571>] tcp_connect+0x53c/0x587 [<ffffffff810c2f0c>] ? getnstimeofday+0x44/0x7d [<ffffffff810c2f56>] ? ktime_get_real+0x11/0x3e [<ffffffff814c6f9b>] tcp_v4_connect+0x3c2/0x431 [<ffffffff814d6913>] __inet_stream_connect+0x84/0x287 [<ffffffff814d6b38>] ? inet_stream_connect+0x22/0x49 [<ffffffff8108d695>] ? _local_bh_enable_ip+0x84/0x9f [<ffffffff8108d6c8>] ? local_bh_enable+0xd/0x11 [<ffffffff8146763c>] ? lock_sock_nested+0x6e/0x79 [<ffffffff814d6b38>] ? inet_stream_connect+0x22/0x49 [<ffffffff814d6b49>] inet_stream_connect+0x33/0x49 [<ffffffff814632c6>] 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 <greearb@candelatech.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Tested-by: Ben Greear <greearb@candelatech.com> Signed-off-by: David S. Miller <davem@davemloft.net>