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Date:   Sat,  3 Oct 2020 17:46:19 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Martin Schiller <ms@....tdt.de>
Cc:     Xie He <xie.he.0141@...il.com>
Subject: [PATCH net] drivers/net/wan: lapb: Replace the skb->len checks with pskb_may_pull

The purpose of these skb->len checks in these drivers is to ensure that
there is a header in the skb available to be read and pulled.

However, we already have the pskb_may_pull function for this purpose.

The pskb_may_pull function also correctly handles non-linear skbs.

(Also delete the word "check" in the comments because pskb_may_pull may
do things other than simple checks in the case of non-linear skbs.)

Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: Martin Schiller <ms@....tdt.de>
Signed-off-by: Xie He <xie.he.0141@...il.com>
---
 drivers/net/wan/hdlc_x25.c  | 4 ++--
 drivers/net/wan/lapbether.c | 4 ++--
 drivers/net/wan/x25_asy.c   | 4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wan/hdlc_x25.c b/drivers/net/wan/hdlc_x25.c
index f52b9fed0593..891a7a918b29 100644
--- a/drivers/net/wan/hdlc_x25.c
+++ b/drivers/net/wan/hdlc_x25.c
@@ -108,9 +108,9 @@ static netdev_tx_t x25_xmit(struct sk_buff *skb, struct net_device *dev)
 	int result;
 
 	/* There should be a pseudo header of 1 byte added by upper layers.
-	 * Check to make sure it is there before reading it.
+	 * Make sure it is there before reading it.
 	 */
-	if (skb->len < 1) {
+	if (!pskb_may_pull(skb, 1)) {
 		kfree_skb(skb);
 		return NETDEV_TX_OK;
 	}
diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index b6be2454b8bd..e0cf692357d6 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -158,9 +158,9 @@ static netdev_tx_t lapbeth_xmit(struct sk_buff *skb,
 		goto drop;
 
 	/* There should be a pseudo header of 1 byte added by upper layers.
-	 * Check to make sure it is there before reading it.
+	 * Make sure it is there before reading it.
 	 */
-	if (skb->len < 1)
+	if (!pskb_may_pull(skb, 1))
 		goto drop;
 
 	switch (skb->data[0]) {
diff --git a/drivers/net/wan/x25_asy.c b/drivers/net/wan/x25_asy.c
index c418767a890a..b935a3e1d5f6 100644
--- a/drivers/net/wan/x25_asy.c
+++ b/drivers/net/wan/x25_asy.c
@@ -308,9 +308,9 @@ static netdev_tx_t x25_asy_xmit(struct sk_buff *skb,
 	}
 
 	/* There should be a pseudo header of 1 byte added by upper layers.
-	 * Check to make sure it is there before reading it.
+	 * Make sure it is there before reading it.
 	 */
-	if (skb->len < 1) {
+	if (!pskb_may_pull(skb, 1)) {
 		kfree_skb(skb);
 		return NETDEV_TX_OK;
 	}
-- 
2.25.1

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