diff options
authorXie He <>2020-07-24 19:33:47 +0300
committerDavid S. Miller <>2020-07-25 06:17:42 +0300
commit8754e1379e7089516a449821f88e1fe1ebbae5e1 (patch)
parent7df5cb75cfb8acf96c7f2342530eb41e0c11f4c3 (diff)
drivers/net/wan: lapb: Corrected the usage of skb_cow
This patch fixed 2 issues with the usage of skb_cow in LAPB drivers "lapbether" and "hdlc_x25": 1) After skb_cow fails, kfree_skb should be called to drop a reference to the skb. But in both drivers, kfree_skb is not called. 2) skb_cow should be called before skb_push so that is can ensure the safety of skb_push. But in "lapbether", it is incorrectly called after skb_push. More details about these 2 issues: 1) The behavior of calling kfree_skb on failure is also the behavior of netif_rx, which is called by this function with "return netif_rx(skb);". So this function should follow this behavior, too. 2) In "lapbether", skb_cow is called after skb_push. This results in 2 logical issues: a) skb_push is not protected by skb_cow; b) An extra headroom of 1 byte is ensured after skb_push. This extra headroom has no use in this function. It also has no use in the upper-layer function that this function passes the skb to (x25_lapb_receive_frame in net/x25/x25_dev.c). So logically skb_cow should instead be called before skb_push. Cc: Eric Dumazet <> Cc: Martin Schiller <> Signed-off-by: Xie He <> Signed-off-by: David S. Miller <>
2 files changed, 8 insertions, 4 deletions
diff --git a/drivers/net/wan/hdlc_x25.c b/drivers/net/wan/hdlc_x25.c
index c84536b03aa8..f70336bb6f52 100644
--- a/drivers/net/wan/hdlc_x25.c
+++ b/drivers/net/wan/hdlc_x25.c
@@ -71,8 +71,10 @@ static int x25_data_indication(struct net_device *dev, struct sk_buff *skb)
unsigned char *ptr;
- if (skb_cow(skb, 1))
+ if (skb_cow(skb, 1)) {
+ kfree_skb(skb);
return NET_RX_DROP;
+ }
skb_push(skb, 1);
diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 284832314f31..b2868433718f 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -128,10 +128,12 @@ static int lapbeth_data_indication(struct net_device *dev, struct sk_buff *skb)
unsigned char *ptr;
- skb_push(skb, 1);
- if (skb_cow(skb, 1))
+ if (skb_cow(skb, 1)) {
+ kfree_skb(skb);
return NET_RX_DROP;
+ }
+ skb_push(skb, 1);
ptr = skb->data;
*ptr = X25_IFACE_DATA;