netdev - [PATCH] ravb: Fix use-after-free ravb_tstamp

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Date:   Fri, 16 Aug 2019 17:17:02 +0200
From:   Simon Horman <horms+renesas@...ge.net.au>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: [PATCH] ravb: Fix use-after-free ravb_tstamp_skb

From: Tho Vu <tho.vu.wh@....renesas.com>

When a Tx timestamp is requested, a pointer to the skb is stored in the
ravb_tstamp_skb struct. This was done without an skb_get. There exists
the possibility that the skb could be freed by ravb_tx_free (when
ravb_tx_free is called from ravb_start_xmit) before the timestamp was
processed, leading to a use-after-free bug.

Use skb_get when filling a ravb_tstamp_skb struct, and add appropriate
frees/consumes when a ravb_tstamp_skb struct is freed.

Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
Signed-off-by: Tho Vu <tho.vu.wh@....renesas.com>
Signed-off-by: Kazuya Mizuguchi <kazuya.mizuguchi.ks@...esas.com>
Signed-off-by: Simon Horman <horms+renesas@...ge.net.au>
---
As this is an old bug I am submitting a fix against net-next rather than
net: I do not see any urgency here. I am however, happy for it to be
applied against net instead.
---
 drivers/net/ethernet/renesas/ravb_main.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index ef8f08931fe8..6cacd5e893ac 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Renesas Ethernet AVB device driver
  *
- * Copyright (C) 2014-2015 Renesas Electronics Corporation
+ * Copyright (C) 2014-2019 Renesas Electronics Corporation
  * Copyright (C) 2015 Renesas Solutions Corp.
  * Copyright (C) 2015-2016 Cogent Embedded, Inc. <source@...entembedded.com>
  *
@@ -513,7 +513,10 @@ static void ravb_get_tx_tstamp(struct net_device *ndev)
 			kfree(ts_skb);
 			if (tag == tfa_tag) {
 				skb_tstamp_tx(skb, &shhwtstamps);
+				dev_consume_skb_any(skb);
 				break;
+			} else {
+				dev_kfree_skb_any(skb);
 			}
 		}
 		ravb_modify(ndev, TCCR, TCCR_TFR, TCCR_TFR);
@@ -1564,7 +1567,7 @@ static netdev_tx_t ravb_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 			}
 			goto unmap;
 		}
-		ts_skb->skb = skb;
+		ts_skb->skb = skb_get(skb);
 		ts_skb->tag = priv->ts_skb_tag++;
 		priv->ts_skb_tag &= 0x3ff;
 		list_add_tail(&ts_skb->list, &priv->ts_skb_list);
@@ -1693,6 +1696,7 @@ static int ravb_close(struct net_device *ndev)
 	/* Clear the timestamp list */
 	list_for_each_entry_safe(ts_skb, ts_skb2, &priv->ts_skb_list, list) {
 		list_del(&ts_skb->list);
+		kfree_skb(ts_skb->skb);
 		kfree(ts_skb);
 	}
 
-- 
2.11.0