wifi: mwifiex: use the subframe length when parsing A-MSDU TDLS frames

In the Linux kernel, the following vulnerability has been resolved: wifi: mwifiex: use the subframe length when parsing A-MSDU TDLS frames mwifiex_11n_dispatch_amsdu_pkt() splits an A-MSDU with ieee80211_amsdu_to_8023s() and walks the resulting subframes. For each subframe it passes the subframe data pointer to mwifiex_process_tdls_action_frame(), but pairs it with skb->len, the length of the A-MSDU parent, instead of rx_skb->len: rx_skb = __skb_dequeue(&list); rx_hdr = (struct rx_packet_hdr *)rx_skb->data; if (ISSUPP_TDLS_ENABLED(priv->adapter->fw_cap_info) && ntohs(rx_hdr->eth803_hdr.h_proto) == ETH_P_TDLS) { mwifiex_process_tdls_action_frame(priv, (u8 *)rx_hdr, skb->len); } The parent is not a valid description of that buffer, and may not be valid memory at all. ieee80211_amsdu_to_8023s() ends with if (!reuse_skb) dev_kfree_skb(skb); and it only sets reuse_skb when the parent is linear, is not a head_frag, and is being consumed as the *last* subframe. So when the parent does not qualify for reuse it has already been freed, and the read of skb->len is a use-after-free. When it is reused, skb->len is the length of the last subframe, applied to every earlier subframe, which over-states the buffer whenever an earlier subframe is shorter. The callee cannot absorb a wrong length, because it derives its own ceiling from the value it is given. Each frame type computes ies_len = len - sizeof(struct ethhdr) - TDLS_*_FIX_LEN; and the element walk is then bounded entirely against that ceiling, for (end = pos + ies_len; pos + 1 < end; pos += 2 + pos[1]) { u8 ie_len = pos[1]; if (pos + 2 + ie_len > end) break; so a too-large len moves end past the end of the subframe and the walk reads and copies beyond it. The A-MSDU layout is chosen by the sender, which makes the difference between the last subframe and a shorter earlier one remotely selectable. Reaching this requires TDLS support in firmware and the TDLS ethertype on the subframe. The other caller, mwifiex_process_rx_packet(), is correct: it passes a pointer and a length that describe the same region of the RX buffer. Pass rx_skb->len, the length of the subframe actually being parsed.