net: usb: sr9700: Handle negative len

Packet len computed as difference of length word extracted from
skb data and four may result in a negative value. In such case
processing of the buffer should be interrupted rather than
setting sr_skb->len to an unexpectedly large value (due to cast
from signed to unsigned integer) and passing sr_skb to
usbnet_skb_return.

Fixes: e9da0b56fe27 ("sr9700: sanity check for packet length")
Signed-off-by: Szymon Heidrich <szymon.heidrich@gmail.com>
Link: https://lore.kernel.org/r/20230114182326.30479-1-szymon.heidrich@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/drivers/net/usb/sr9700.c b/drivers/net/usb/sr9700.c
index 5a53e63d33a60995ea8023474e664f6fc14017a5..3164451e1010cc80a67e2fddc89a9e59a6721cab 100644 (file)
--- a/drivers/net/usb/sr9700.c
+++ b/drivers/net/usb/sr9700.c
@@ -413,7 +413,7 @@ static int sr9700_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
                /* ignore the CRC length */
                len = (skb->data[1] | (skb->data[2] << 8)) - 4;
 
-               if (len > ETH_FRAME_LEN || len > skb->len)
+               if (len > ETH_FRAME_LEN || len > skb->len || len < 0)
                        return 0;
 
                /* the last packet of current skb */