[bug report] net: wwan: Add Qualcomm BAM-DMUX WWAN network driver

[Dan Carpenter <dan.carpenter@linaro.org>]

[ Smatch checking is paused while we raise funding.  #SadFace
  https://lore.kernel.org/all/aTaiGSbWZ9DJaGo7@stanley.mountain/ -dan ]

Hello Stephan Gerhold,

Commit 21a0ffd9b38c ("net: wwan: Add Qualcomm BAM-DMUX WWAN network
driver") from Nov 27, 2021 (linux-next), leads to the following
Smatch static checker warning:

	drivers/net/wwan/qcom_bam_dmux.c:505 bam_dmux_cmd_data()
	error: buffer overflow 'dmux->netdevs' 8 <= 255 user_rl='0-255' uncapped

drivers/net/wwan/qcom_bam_dmux.c
    500 static void bam_dmux_cmd_data(struct bam_dmux_skb_dma *skb_dma)
    501 {
    502         struct bam_dmux *dmux = skb_dma->dmux;
    503         struct sk_buff *skb = skb_dma->skb;
    504         struct bam_dmux_hdr *hdr = (struct bam_dmux_hdr *)skb->data;
--> 505         struct net_device *netdev = dmux->netdevs[hdr->ch];
                                                          ^^^^^^^
Smatch thinks skb->data is untrusted.  This is the rx path.

    506 
    507         if (!netdev || !netif_running(netdev)) {
    508                 dev_warn(dmux->dev, "Data for inactive channel %u\n", hdr->ch);
    509                 return;
    510         }
    511 

regards,
dan carpenter