[PATCH] net: fix memory leaks in flush_backlog() with RPS

[Qian Cai]

netif_receive_skb_list_internal() could call enqueue_to_backlog() to put
some skb to softnet_data.input_pkt_queue and then in
ip_route_input_slow(), it allocates a dst_entry to be used in
skb_dst_set(). Later,

cleanup_net
  default_device_exit_batch
    unregister_netdevice_many
      rollback_registered_many
        flush_all_backlogs

will call flush_backlog() for all CPUs which would call kfree_skb() for
each skb on the input_pkt_queue without calling skb_dst_drop() first.

unreferenced object 0xffff97008e4c4040 (size 176):
 comm "softirq", pid 0, jiffies 4295173845 (age 32012.550s)
 hex dump (first 32 bytes):
   00 d0 a5 74 04 97 ff ff 40 72 1a 96 ff ff ff ff  ...t....@xxxxxxx
   c1 a3 c5 95 ff ff ff ff 00 00 00 00 00 00 00 00  ................
 backtrace:
   [<0000000030483fae>] kmem_cache_alloc+0x184/0x430
   [<000000007ae17545>] dst_alloc+0x8e/0x128
   [<000000001efe9a1f>] rt_dst_alloc+0x6f/0x1e0
   rt_dst_alloc at net/ipv4/route.c:1628
   [<00000000e67d4dac>] ip_route_input_rcu+0xdfe/0x1640
   ip_route_input_slow at net/ipv4/route.c:2218
   (inlined by) ip_route_input_rcu at net/ipv4/route.c:2348
   [<000000009f30cbc0>] ip_route_input_noref+0xab/0x1a0
   [<000000004f53bd04>] arp_process+0x83a/0xf50
   arp_process at net/ipv4/arp.c:813 (discriminator 1)
   [<0000000061fd547d>] arp_rcv+0x276/0x330
   [<0000000007dbfa7a>] __netif_receive_skb_list_core+0x4d2/0x500
   [<0000000062d5f6d2>] netif_receive_skb_list_internal+0x4cb/0x7d0
   [<000000002baa2b74>] gro_normal_list+0x55/0xc0
   [<0000000093d04885>] napi_complete_done+0xea/0x350
   [<00000000467dd088>] tg3_poll_msix+0x174/0x310 [tg3]
   [<00000000498af7d9>] net_rx_action+0x278/0x890
   [<000000001e81d7e6>] __do_softirq+0xd9/0x589
   [<00000000087ee354>] irq_exit+0xa2/0xc0
   [<000000001c4db0cd>] do_IRQ+0x87/0x180

Signed-off-by: Qian Cai <cai@xxxxxx>
---
 net/core/dev.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 522288177bbd..b898cd3036da 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5496,6 +5496,7 @@ static void flush_backlog(struct work_struct *work)
 	skb_queue_walk_safe(&sd->input_pkt_queue, skb, tmp) {
 		if (skb->dev->reg_state == NETREG_UNREGISTERING) {
 			__skb_unlink(skb, &sd->input_pkt_queue);
+			skb_dst_drop(skb);
 			kfree_skb(skb);
 			input_queue_head_incr(sd);
 		}
-- 
2.21.0 (Apple Git-122.2)