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

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.

Fixes: 776f742040ca ("mwifiex: fix AMPDU not setup on TDLS link problem")
Assisted-by: Codex:gpt-5.6-sol
Assisted-by: Kimi:K3
Cc: stable@vger.kernel.org
Signed-off-by: Zhao Li <enderaoelyther@gmail.com>
Link: https://patch.msgid.link/20260728115325.19128-1-enderaoelyther@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>