[PATCH v2] net: usb: smsc95xx: Limit packet length to skb->len

[Szymon Heidrich <szymon.heidrich@gmail.com>]

Packet length retrieved from descriptor may be larger than
the actual socket buffer length. In such case the cloned
skb passed up the network stack will leak kernel memory contents.

Fixes: 2f7ca802bdae ("net: Add SMSC LAN9500 USB2.0 10/100 ethernet adapter driver")
Signed-off-by: Szymon Heidrich <szymon.heidrich@gmail.com>
---
V1 -> V2: Move packet length check to prevent kernel panic in skb_pull

 drivers/net/usb/smsc95xx.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index 32d2c60d3..563ecd27b 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -1833,6 +1833,12 @@ static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 		size = (u16)((header & RX_STS_FL_) >> 16);
 		align_count = (4 - ((size + NET_IP_ALIGN) % 4)) % 4;
 
+		if (unlikely(size > skb->len)) {
+			netif_dbg(dev, rx_err, dev->net,
+				  "size err header=0x%08x\n", header);
+			return 0;
+		}
+
 		if (unlikely(header & RX_STS_ES_)) {
 			netif_dbg(dev, rx_err, dev->net,
 				  "Error header=0x%08x\n", header);
-- 
2.40.0