linux-kernel - [PATCH net-next] net: dsa: avoid potential use-after-free error

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Message-ID: <20201118154335.1189-1-ceggers@arri.de>
Date:   Wed, 18 Nov 2020 16:43:35 +0100
From:   Christian Eggers <ceggers@...i.de>
To:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>
CC:     Vivien Didelot <vivien.didelot@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Christian Eggers <ceggers@...i.de>
Subject: [PATCH net-next] net: dsa: avoid potential use-after-free error

If dsa_switch_ops::port_txtstamp() returns false, clone will be freed
immediately. Storing the pointer in DSA_SKB_CB(skb)->clone anyway,
supports annoying use-after-free bugs.

Signed-off-by: Christian Eggers <ceggers@...i.de>
Fixes 146d442c2357 ("net: dsa: Keep a pointer to the skb clone for TX timestamping")
---
 net/dsa/slave.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index ff2266d2b998..7efc753e4d9d 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -522,10 +522,10 @@ static void dsa_skb_tx_timestamp(struct dsa_slave_priv *p,
 	if (!clone)
 		return;

-	DSA_SKB_CB(skb)->clone = clone;
-
-	if (ds->ops->port_txtstamp(ds, p->dp->index, clone, type))
+	if (ds->ops->port_txtstamp(ds, p->dp->index, clone, type)) {
+		DSA_SKB_CB(skb)->clone = clone;
 		return;
+	}

 	kfree_skb(clone);
 }
-- 
Christian Eggers
Embedded software developer

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