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Date:   Wed, 14 Oct 2020 18:17:19 +0200
From:   Christian Eggers <>
To:     Woojung Huh <>,
        Andrew Lunn <>,
        Vivien Didelot <>,
        Florian Fainelli <>,
        Vladimir Oltean <>
CC:     Microchip Linux Driver Support <>,
        "David S . Miller" <>,
        Jakub Kicinski <>, <>,
        <>, Christian Eggers <>
Subject: [PATCH net] net: dsa: ksz: fix padding size of skb

__skb_put_padto() is called in order to ensure a minimal size of the
sk_buff. The required minimal size is ETH_ZLEN + the size required for
the tail tag.

The current argument misses the size for the tail tag. The expression
"skb->len + padlen" can be simplified to ETH_ZLEN.

Too small sk_buffs typically result from cloning in
dsa_skb_tx_timestamp(). The cloned sk_buff may not meet the minimum size

Fixes: e71cb9e00922 ("net: dsa: ksz: fix skb freeing")
Signed-off-by: Christian Eggers <>
 net/dsa/tag_ksz.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
index 945a9bd5ba35..8ef2085349e7 100644
--- a/net/dsa/tag_ksz.c
+++ b/net/dsa/tag_ksz.c
@@ -24,7 +24,7 @@ static struct sk_buff *ksz_common_xmit(struct sk_buff *skb,
 	if (skb_tailroom(skb) >= padlen + len) {
 		/* Let dsa_slave_xmit() free skb */
-		if (__skb_put_padto(skb, skb->len + padlen, false))
+		if (__skb_put_padto(skb, ETH_ZLEN + len, false))
 			return NULL;
 		nskb = skb;
@@ -45,7 +45,7 @@ static struct sk_buff *ksz_common_xmit(struct sk_buff *skb,
 		/* Let skb_put_padto() free nskb, and let dsa_slave_xmit() free
 		 * skb
-		if (skb_put_padto(nskb, nskb->len + padlen))
+		if (skb_put_padto(nskb, ETH_ZLEN + len))
 			return NULL;
Christian Eggers
Embedded software developer

Arnold & Richter Cine Technik GmbH & Co. Betriebs KG
Sitz: Muenchen - Registergericht: Amtsgericht Muenchen - Handelsregisternummer: HRA 57918
Persoenlich haftender Gesellschafter: Arnold & Richter Cine Technik GmbH
Sitz: Muenchen - Registergericht: Amtsgericht Muenchen - Handelsregisternummer: HRB 54477
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