[PATCH AUTOSEL 5.4 052/130] net: dsa: avoid potential use-after-free error

[Sasha Levin]

From: Christian Eggers <ceggers@xxxxxxx>

[ Upstream commit 30abc9cd9c6bdd44d23fc49a9c2526a86fba4305 ]

If dsa_switch_ops::port_txtstamp() returns false, clone will be freed
immediately. Shouldn't store a pointer to freed memory.

Signed-off-by: Christian Eggers <ceggers@xxxxxxx>
Reviewed-by: Vladimir Oltean <olteanv@xxxxxxxxx>
Tested-by: Vladimir Oltean <olteanv@xxxxxxxxx>
Reviewed-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
Link: https://lore.kernel.org/r/20201119110906.25558-1-ceggers@xxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 f734ce0bcb56e..2b657e88d8017 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -476,10 +476,10 @@ 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);
 }
-- 
2.27.0