[PATCH v3] net: usb: lan78xx: Limit packet length to skb->len

[PATCH v3] net: usb: lan78xx: Limit packet length to skb->len

[Szymon Heidrich]

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.

Additionally prevent integer underflow when size is less than
ETH_FCS_LEN.

Fixes: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
Signed-off-by: Szymon Heidrich <szymon.heidrich@gmail.com>
---
V1 -> V2: Fix ISO C90 forbids mixed declarations and code
V2 -> V3: Removed the Reported-by tag

 drivers/net/usb/lan78xx.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 068488890..c458c030f 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -3579,13 +3579,29 @@ static int lan78xx_rx(struct lan78xx_net *dev, struct sk_buff *skb,
 		size = (rx_cmd_a & RX_CMD_A_LEN_MASK_);
 		align_count = (4 - ((size + RXW_PADDING) % 4)) % 4;
 
+		if (unlikely(size > skb->len)) {
+			netif_dbg(dev, rx_err, dev->net,
+				  "size err rx_cmd_a=0x%08x\n",
+				  rx_cmd_a);
+			return 0;
+		}
+
 		if (unlikely(rx_cmd_a & RX_CMD_A_RED_)) {
 			netif_dbg(dev, rx_err, dev->net,
 				  "Error rx_cmd_a=0x%08x", rx_cmd_a);
 		} else {
-			u32 frame_len = size - ETH_FCS_LEN;
+			u32 frame_len;
 			struct sk_buff *skb2;
 
+			if (unlikely(size < ETH_FCS_LEN)) {
+				netif_dbg(dev, rx_err, dev->net,
+					  "size err rx_cmd_a=0x%08x\n",
+					  rx_cmd_a);
+				return 0;
+			}
+
+			frame_len = size - ETH_FCS_LEN;
+
 			skb2 = napi_alloc_skb(&dev->napi, frame_len);
 			if (!skb2)
 				return 0;
-- 
2.40.0

Re: [PATCH v3] net: usb: lan78xx: Limit packet length to skb->len

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by David S. Miller <davem@davemloft.net>:

On Sat, 18 Mar 2023 10:25:52 +0100 you wrote:
> 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.
> 
> Additionally prevent integer underflow when size is less than
> ETH_FCS_LEN.
> 
> [...]

Here is the summary with links:
  - [v3] net: usb: lan78xx: Limit packet length to skb->len
    https://git.kernel.org/netdev/net/c/7f247f5a2c18

You are awesome, thank you!
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