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Date:   Mon, 23 Sep 2019 17:02:46 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     network dev <netdev@...r.kernel.org>
Cc:     davem@...emloft.net, Sabrina Dubroca <sd@...asysnail.net>,
        Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net] macsec: drop skb sk before calling gro_cells_receive

Fei Liu reported a crash when doing netperf on a topo of macsec
dev over veth:

  [  448.919128] refcount_t: underflow; use-after-free.
  [  449.090460] Call trace:
  [  449.092895]  refcount_sub_and_test+0xb4/0xc0
  [  449.097155]  tcp_wfree+0x2c/0x150
  [  449.100460]  ip_rcv+0x1d4/0x3a8
  [  449.103591]  __netif_receive_skb_core+0x554/0xae0
  [  449.108282]  __netif_receive_skb+0x28/0x78
  [  449.112366]  netif_receive_skb_internal+0x54/0x100
  [  449.117144]  napi_gro_complete+0x70/0xc0
  [  449.121054]  napi_gro_flush+0x6c/0x90
  [  449.124703]  napi_complete_done+0x50/0x130
  [  449.128788]  gro_cell_poll+0x8c/0xa8
  [  449.132351]  net_rx_action+0x16c/0x3f8
  [  449.136088]  __do_softirq+0x128/0x320

The issue was caused by skb's true_size changed without its sk's
sk_wmem_alloc increased in tcp/skb_gro_receive(). Later when the
skb is being freed and the skb's truesize is subtracted from its
sk's sk_wmem_alloc in tcp_wfree(), underflow occurs.

macsec is calling gro_cells_receive() to receive a packet, which
actually requires skb->sk to be NULL. However when macsec dev is
over veth, it's possible the skb->sk is still set if the skb was
not unshared or expanded from the peer veth.

ip_rcv() is calling skb_orphan() to drop the skb's sk for tproxy,
but it is too late for macsec's calling gro_cells_receive(). So
fix it by dropping the skb's sk earlier on rx path of macsec.

Fixes: 5491e7c6b1a9 ("macsec: enable GRO and RPS on macsec devices")
Reported-by: Xiumei Mu <xmu@...hat.com>
Reported-by: Fei Liu <feliu@...hat.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 drivers/net/macsec.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 8f46aa1..cb76373 100644
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -1235,6 +1235,7 @@ static rx_handler_result_t macsec_handle_frame(struct sk_buff **pskb)
 		macsec_rxsa_put(rx_sa);
 	macsec_rxsc_put(rx_sc);
 
+	skb_orphan(skb);
 	ret = gro_cells_receive(&macsec->gro_cells, skb);
 	if (ret == NET_RX_SUCCESS)
 		count_rx(dev, skb->len);
-- 
2.1.0

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