From: Xie He <xie.he.0141@xxxxxxxxx>
[ Upstream commit 8754e1379e7089516a449821f88e1fe1ebbae5e1 ]
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 <edumazet@xxxxxxxxxx>
Cc: Martin Schiller <ms@xxxxxxxxxx>
Signed-off-by: Xie He <xie.he.0141@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/net/wan/hdlc_x25.c | 4 +++-
drivers/net/wan/lapbether.c | 8 +++++---
2 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/net/wan/hdlc_x25.c b/drivers/net/wan/hdlc_x25.c
index bf78073ee7fd9..e2a83f4cd3bb6 100644
--- a/drivers/net/wan/hdlc_x25.c
+++ b/drivers/net/wan/hdlc_x25.c
@@ -62,8 +62,10 @@ 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);
skb_reset_network_header(skb);
diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 0f1217b506ad2..65b2202647411 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;
--
2.25.1
