[PATCH 08/10] net: usb: smsc95xx: don't blindly trust hardware size

[Ahmad Fatoum]

This is a port of Linux commit ff821092cf02a70c2bccd2d19269f01e29aa52cf:

| Author:     Szymon Heidrich <szymon.heidrich at gmail.com>
| AuthorDate: Thu Mar 16 11:19:54 2023 +0100
|
| net: usb: smsc95xx: Limit packet length to skb->len
|
| 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 at gmail.com>
| Reviewed-by: Jakub Kicinski <kuba at kernel.org>
| Link: https://lore.kernel.org/r/20230316101954.75836-1-szymon.heidrich@gmail.com
| Signed-off-by: Jakub Kicinski <kuba at kernel.org>

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 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 ab0059fcdb0f..1587128368ad 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -767,6 +767,12 @@ static int smsc95xx_rx_fixup(struct usbnet *dev, void *buf, int len)
 		size = (u16)((header & RX_STS_FL_) >> 16);
 		align_count = (4 - ((size + NET_IP_ALIGN) % 4)) % 4;
 
+		if (unlikely(size > len)) {
+			netif_dbg(dev, rx_err, dev->net,
+				  "size err header=0x%08x\n", header);
+			return 0;
+		}
+
 		if (header & RX_STS_ES_) {
 			netif_dbg(dev, rx_err, dev->net,
 				  "Error header=0x%08x\n", header);
-- 
2.39.2