[PATCH v2] net: usb: lan78xx: Limit packet length to skb->len

From: Szymon Heidrich <szymon.heidrich@gmail.com>
To: woojung.huh@microchip.com, UNGLinuxDriver@microchip.com,
	kuba@kernel.org, davem@davemloft.net, edumazet@google.com
Cc: pabeni@redhat.com, szymon.heidrich@gmail.com,
	linux-usb@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, kernel test robot <lkp@intel.com>
Subject: [PATCH v2] net: usb: lan78xx: Limit packet length to skb->len
Date: Fri, 17 Mar 2023 18:36:06 +0100	[thread overview]
Message-ID: <20230317173606.91426-1-szymon.heidrich@gmail.com> (raw)
In-Reply-To: <202303180031.EsiDo4qY-lkp@intel.com>

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>
Reported-by: kernel test robot <lkp@intel.com>
---
V1 -> V2: Fix ISO C90 forbids mixed declarations and code

 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..a150711a1 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -3579,11 +3579,27 @@ 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;
+
+			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;
 			struct sk_buff *skb2;
 
 			skb2 = napi_alloc_skb(&dev->napi, frame_len);
-- 
2.40.0

