[bug report] net: ethernet: mtk_wed: introduce wed mcu support

[Dan Carpenter]

Hello Sujuan Chen,

The patch cc514101a97e: "net: ethernet: mtk_wed: introduce wed mcu
support" from Nov 5, 2022, leads to the following Smatch static
checker warning:

	drivers/net/ethernet/mediatek/mtk_wed_mcu.c:82 mtk_wed_update_rx_stats()
	warn: uncapped user loop index 'i'

drivers/net/ethernet/mediatek/mtk_wed_mcu.c
    64 static void
    65 mtk_wed_update_rx_stats(struct mtk_wed_device *wed, struct sk_buff *skb)
    66 {
    67         u32 count = get_unaligned_le32(skb->data);
    68         struct mtk_wed_wo_rx_stats *stats;
    69         int i;
    70 
    71         if (count * sizeof(*stats) > skb->len - sizeof(u32))
    72                 return;

There are two issues.

Bug 1: There is no check that skb->len >= sizeof(u32) so the
get_unaligned_le32(skb->data); can result in an out of bounds read and
the bounds check on count is not effective.

Bug 2: On a 32bit system the "count * sizeof(*stats)" multiplication can
have an integer overflow bug.  Suggestion:

	if (size_mul(count, sizeof(*stats)) > skb->len - sizeof(u32))
		return;

    73 
    74         stats = (struct mtk_wed_wo_rx_stats *)(skb->data + sizeof(u32));
    75         for (i = 0 ; i < count ; i++)
--> 76                 wed->wlan.update_wo_rx_stats(wed, &stats[i]);
    77 }

regards,
dan carpenter