[PATCH net v2] net: usb: sr9700: include receive overhead in the length check

[Pengpeng Hou <hppiscas@163.com>]

The receive fixup subtracts the Ethernet CRC from the reported packet
length, but compares that payload length against the whole remaining
receive buffer. The following copy starts after the three-byte header,
and the cursor advance consumes both that header and the four-byte CRC.

Require the payload to fit after SR_RX_OVERHEAD before copying it or
advancing to the next packet. The loop already ensures that the
remaining buffer is larger than the overhead, so the subtraction is
safe.

The issue was found by our static-analysis tool.

Fixes: c9b37458e956 ("USB2NET : SR9700 : One chip USB 1.1 USB2NET SR9700Device Driver Support")
Reviewed-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Tested-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Assisted-by: gpt 5
Signed-off-by: Pengpeng Hou <hppiscas@163.com>
---
Changes since v1:
https://lore.kernel.org/all/20260705083724.24494-1-pengpeng@iscas.ac.cn/
Clarify the subject as Andrew and Ethan requested. This is a revision of
the previously withdrawn queue entry, not a new bug report.

 drivers/net/usb/sr9700.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/sr9700.c b/drivers/net/usb/sr9700.c
index 937e6fef3ac6..50981a28376a 100644
--- a/drivers/net/usb/sr9700.c
+++ b/drivers/net/usb/sr9700.c
@@ -355,7 +355,8 @@ 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 || len < 0)
+		if (len > ETH_FRAME_LEN || len < 0 ||
+		    len > skb->len - SR_RX_OVERHEAD)
 			return 0;
 
 		/* the last packet of current skb */

base-commit: 518e5b794c06c0f0eb40df3e202274a66202c137
-- 
2.50.1 (Apple Git-155)