netdev - [RFC] sierra: avoid trailing bytes leading to garbage parsing

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Message-Id: <20220217103057.10184-1-oneukum@suse.com>
Date:   Thu, 17 Feb 2022 11:30:57 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     steve.glendinning@...well.net, linux-usb@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     Oliver Neukum <oneukum@...e.com>
Subject: [RFC] sierra: avoid trailing bytes leading to garbage parsing

The driver's main loop isn't ready for a device sending
some trailing bytes as it tests for an exact match between
package and accumulated frames.
We would parse some garbage from the heap and follow its
pointers.

Signed-off-by: Oliver Neukum <oneukum@...e.com>
---
 drivers/net/usb/smsc75xx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/smsc75xx.c b/drivers/net/usb/smsc75xx.c
index 95de452ff4da..649e43b4df4f 100644
--- a/drivers/net/usb/smsc75xx.c
+++ b/drivers/net/usb/smsc75xx.c
@@ -2183,7 +2183,8 @@ static int smsc75xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 	if (skb->len < dev->net->hard_header_len)
 		return 0;
 
-	while (skb->len > 0) {
+	/* at least two u32 must be left to go on */
+	while (skb->len > 4 + 4) {
 		u32 rx_cmd_a, rx_cmd_b, align_count, size;
 		struct sk_buff *ax_skb;
 		unsigned char *packet;
-- 
2.34.1