netdev - [PATCH v4 1/3] can: dev: can_restart: fix use after free bug

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Date:   Wed, 20 Jan 2021 20:41:35 +0900
From:   Vincent Mailhol <mailhol.vincent@...adoo.fr>
To:     Marc Kleine-Budde <mkl@...gutronix.de>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        linux-can@...r.kernel.org
Cc:     netdev@...r.kernel.org, Wolfgang Grandegger <wg@...ndegger.com>,
        Stephane Grosjean <s.grosjean@...k-system.com>,
        Loris Fauster <loris.fauster@...ontrol.com>,
        Alejandro Concepcion Rodriguez <alejandro@...ro.eu>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>
Subject: [PATCH v4 1/3] can: dev: can_restart: fix use after free bug

After calling netif_rx_ni(skb), dereferencing skb is unsafe.
Especially, the can_frame cf which aliases skb memory is accessed
after the netif_rx_ni() in:
      stats->rx_bytes += cf->len;

Reordering the lines solves the issue.

Fixes: 39549eef3587 ("can: CAN Network device driver and Netlink interface")
Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
---
*Remark for upstream*
drivers/net/can/dev.c has been moved to drivers/net/can/dev/dev.c in
below commit, please carry the patch forward.
Reference: 3e77f70e7345 ("can: dev: move driver related infrastructure
into separate subdir")
---
 drivers/net/can/dev.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 3486704c8a95..8b1ae023cb21 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -592,11 +592,11 @@ static void can_restart(struct net_device *dev)
 
 	cf->can_id |= CAN_ERR_RESTARTED;
 
-	netif_rx_ni(skb);
-
 	stats->rx_packets++;
 	stats->rx_bytes += cf->len;
 
+	netif_rx_ni(skb);
+
 restart:
 	netdev_dbg(dev, "restarted\n");
 	priv->can_stats.restarts++;
-- 
2.26.2