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

Overview

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.

Affected

• Linux >= 776f742040ca5eb6242c60f29ac73d5752a5b621 < 707664027bb9307f7268eda403af7c4ccd9b8644
• Linux >= 776f742040ca5eb6242c60f29ac73d5752a5b621 < 3b02275833a0d3e6583627995d614fa99bdf364f
• Linux >= 776f742040ca5eb6242c60f29ac73d5752a5b621 < a1f0f7dc7eb15754e6931b433edb7beb754c996a
• Linux >= 776f742040ca5eb6242c60f29ac73d5752a5b621 < 25e5a3fe4f15e30f74eca42cbf3bcc3a3fbeda79
• Linux >= 776f742040ca5eb6242c60f29ac73d5752a5b621 < ece2ebb34247d573142617dfc534a9dc11ba59be
• Linux >= 776f742040ca5eb6242c60f29ac73d5752a5b621 < c9dcfe6b8b71369e1d732e2ff622c3696a2f032c
• Linux >= 776f742040ca5eb6242c60f29ac73d5752a5b621 < 5a21ab03829cb6d2682c127f22e2b9cd63b4393f
• Linux >= 776f742040ca5eb6242c60f29ac73d5752a5b621 < 99a948382af8a225e2d5e54a7052158cd6281cc6
• Linux 4.5

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.