mt76: mt7915: introduce 802.11ax multi-bss support

Hello Lorenzo Bianconi,

The patch 6b7f9aff7c67: "mt76: mt7915: introduce 802.11ax multi-bss support" from Mar 15, 2022, leads to the following Smatch static checker warning:

	drivers/net/wireless/mediatek/mt76/mt7915/mcu.c:1872 mt7915_mcu_beacon_mbss()
	error: undefined (user controlled) shift '(((1))) << (data[2])'

drivers/net/wireless/mediatek/mt76/mt7915/mcu.c

    1828 static void
    1829 mt7915_mcu_beacon_mbss(struct sk_buff *rskb, struct sk_buff *skb,
    1830                        struct ieee80211_vif *vif, struct bss_info_bcn *bcn,
    1831                        struct ieee80211_mutable_offsets *offs)
    1832 {
    1833         struct bss_info_bcn_mbss *mbss;
    1834         const struct element *elem;
    1835         struct tlv *tlv;
    1836 
    1837         if (!vif->bss_conf.bssid_indicator)
    1838                 return;
    1839 
    1840         tlv = mt7915_mcu_add_nested_subtlv(rskb, BSS_INFO_BCN_MBSSID,
    1841                                            sizeof(*mbss), &bcn->sub_ntlv,
    1842                                            &bcn->len);
    1843 
    1844         mbss = (struct bss_info_bcn_mbss *)tlv;
    1845         mbss->offset[0] = cpu_to_le16(offs->tim_offset);
    1846         mbss->bitmap = cpu_to_le32(1);
    1847 
    1848         for_each_element_id(elem, WLAN_EID_MULTIPLE_BSSID,
    1849                             &skb->data[offs->mbssid_off],
    1850                             skb->len - offs->mbssid_off) {
    1851                 const struct element *sub_elem;
    1852 
    1853                 if (elem->datalen < 2)
    1854                         continue;
    1855 
    1856                 for_each_element(sub_elem, elem->data + 1, elem->datalen - 1) {
    1857                         const u8 *data;
    1858 
    1859                         if (sub_elem->id || sub_elem->datalen < 4)
    1860                                 continue; /* not a valid BSS profile */
    1861 
    1862                         /* Find WLAN_EID_MULTI_BSSID_IDX
    1863                          * in the merged nontransmitted profile
    1864                          */
    1865                         data = cfg80211_find_ie(WLAN_EID_MULTI_BSSID_IDX,
    1866                                                 sub_elem->data,
    1867                                                 sub_elem->datalen);
    1868                         if (!data || data[1] < 1 || !data[2])

This probably needs a "|| data[2] > 31" but maybe using a define?

    1869                                 continue;
    1870 
    1871                         mbss->offset[data[2]] = cpu_to_le16(data - skb->data);
--> 1872                         mbss->bitmap |= cpu_to_le32(BIT(data[2]));
    1873                 }
    1874         }
    1875 }

regards,
dan carpenter

I do not think it is a real issue since bssid_index is supposed to be limited by mbssid_max_interfaces (set to 16 for 7915), but I will add a check. Thanks.

Regards,
Lorenzo