net: Fix skb consume leak in sch_handle_egress

Fix a memory leak for the tc egress path with TC_ACT_{STOLEN,QUEUED,TRAP}:

  [...]
  unreferenced object 0xffff88818bcb4f00 (size 232):
  comm "softirq", pid 0, jiffies 4299085078 (age 134.028s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 80 70 61 81 88 ff ff 00 41 31 14 81 88 ff ff  ..pa.....A1.....
  backtrace:
    [<ffffffff9991b938>] kmem_cache_alloc_node+0x268/0x400
    [<ffffffff9b3d9231>] __alloc_skb+0x211/0x2c0
    [<ffffffff9b3f0c7e>] alloc_skb_with_frags+0xbe/0x6b0
    [<ffffffff9b3bf9a9>] sock_alloc_send_pskb+0x6a9/0x870
    [<ffffffff9b6b3f00>] __ip_append_data+0x14d0/0x3bf0
    [<ffffffff9b6ba24e>] ip_append_data+0xee/0x190
    [<ffffffff9b7e1496>] icmp_push_reply+0xa6/0x470
    [<ffffffff9b7e4030>] icmp_reply+0x900/0xa00
    [<ffffffff9b7e42e3>] icmp_echo.part.0+0x1a3/0x230
    [<ffffffff9b7e444d>] icmp_echo+0xcd/0x190
    [<ffffffff9b7e9566>] icmp_rcv+0x806/0xe10
    [<ffffffff9b699bd1>] ip_protocol_deliver_rcu+0x351/0x3d0
    [<ffffffff9b699f14>] ip_local_deliver_finish+0x2b4/0x450
    [<ffffffff9b69a234>] ip_local_deliver+0x174/0x1f0
    [<ffffffff9b69a4b2>] ip_sublist_rcv_finish+0x1f2/0x420
    [<ffffffff9b69ab56>] ip_sublist_rcv+0x466/0x920
  [...]

I was able to reproduce this via:

  ip link add dev dummy0 type dummy
  ip link set dev dummy0 up
  tc qdisc add dev eth0 clsact
  tc filter add dev eth0 egress protocol ip prio 1 u32 match ip protocol 1 0xff action mirred egress redirect dev dummy0
  ping 1.1.1.1
  <stolen>

After the fix, there are no kmemleak reports with the reproducer. This is
in line with what is also done on the ingress side, and from debugging the
skb_unref(skb) on dummy xmit and sch_handle_egress() side, it is visible
that these are two different skbs with both skb_unref(skb) as true. The two
seen skbs are due to mirred doing a skb_clone() internally as use_reinsert
is false in tcf_mirred_act() for egress. This was initially reported by Gal.

Fixes: e420bed ("bpf: Add fd-based tcx multi-prog infra with link support")
Reported-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/bdfc2640-8f65-5b56-4472-db8e2b161aab@nvidia.com
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -4061,6 +4061,7 @@ sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
 	case TC_ACT_STOLEN:
 	case TC_ACT_QUEUED:
 	case TC_ACT_TRAP:
+		consume_skb(skb);
 		*ret = NET_XMIT_SUCCESS;
 		return NULL;
 	}