From a9ce4053dc945c5372dedba5017ee675b30dc0c5 Mon Sep 17 00:00:00 2001 From: Mark Amirkan Date: Sun, 13 Sep 2026 17:14:09 -0700 Subject: [PATCH] net: lan743x: fix RX checksum use-after-free lan743x_rx_process_buffer() adds each non-first receive buffer to the head skb's frag_list. On the last descriptor, lan743x_rx_trim_skb() linearizes the head and frees the fragment skb metadata. The checksum-success path then writes ip_summed through the local skb pointer, which still points to the final fragment. This causes a use-after-free write when a packet spans more than one receive buffer. Set ip_summed on the surviving head skb instead. Multi-buffer receive can occur after a live MTU increase because existing ring entries keep their old buffer size until they are replenished. A KUnit test invoking lan743x_rx_process_buffer() with a two-buffer packet produced a one-byte KASAN use-after-free write before this change. The same test passed after the change. The driver object also builds with W=1. This was not tested on physical LAN743x hardware. Fixes: cd6910501cfd ("net: lan743x: Add support for Rx IP & TCP checksum offload") Cc: stable@vger.kernel.org Signed-off-by: Mark Amirkan Reviewed-by: Chenguang Zhao Link: https://patch.msgid.link/20260913-b4-send-lan743x-uaf-v1-1-73d563d08ba9@gmail.com Signed-off-by: Jakub Kicinski --- drivers/net/ethernet/microchip/lan743x_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/ethernet/microchip/lan743x_main.c b/drivers/net/ethernet/microchip/lan743x_main.c index 24ae56a3c9ed..82d3ec20ba25 100644 --- a/drivers/net/ethernet/microchip/lan743x_main.c +++ b/drivers/net/ethernet/microchip/lan743x_main.c @@ -2604,7 +2604,7 @@ static int lan743x_rx_process_buffer(struct lan743x_rx *rx) rx->adapter->netdev); if (rx->adapter->netdev->features & NETIF_F_RXCSUM) { if (!is_ice && !is_tce && !is_icsm) - skb->ip_summed = CHECKSUM_UNNECESSARY; + rx->skb_head->ip_summed = CHECKSUM_UNNECESSARY; } netdev_dbg(netdev, "sending %d byte frame to OS", rx->skb_head->len);