6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mark Amirkan commit a9ce4053dc945c5372dedba5017ee675b30dc0c5 upstream. 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 Signed-off-by: Greg Kroah-Hartman --- drivers/net/ethernet/microchip/lan743x_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/net/ethernet/microchip/lan743x_main.c +++ b/drivers/net/ethernet/microchip/lan743x_main.c @@ -2726,7 +2726,7 @@ process_extension: 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);