[PATCH] wifi: mac80211: capture fast-RX rate before mesh reuses skb->cb

[Zhao Li <enderaoelyther@gmail.com>]

ieee80211_invoke_fast_rx() reads RX status through
IEEE80211_SKB_RXCB(skb), which aliases the same skb->cb storage
that ieee80211_rx_mesh_data() reuses as IEEE80211_TX_INFO.  In the
unicast forward path, mesh_data does:

	info = IEEE80211_SKB_CB(fwd_skb);
	memset(info, 0, sizeof(*info));

on the same skb the caller still names via rx->skb, then either
queues the skb for TX (success) or kfree_skb()'s it (no-route)
before returning RX_QUEUED.  The caller's RX_QUEUED arm then
calls sta_stats_encode_rate(status) on memory that is either
zeroed (success path) or freed (no-route path).  The latter is
KASAN slab-use-after-free in ieee80211_prepare_and_rx_handle.

Fix by encoding the rate from status before invoking
ieee80211_rx_mesh_data(), so the RX_QUEUED arm consumes a value
captured while status was still backed by valid memory.

Fixes: 3468e1e0c639 ("wifi: mac80211: add mesh fast-rx support")
Cc: stable@vger.kernel.org
Signed-off-by: Zhao Li <enderaoelyther@gmail.com>
---
 net/mac80211/rx.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -4984,6 +4984,7 @@ static bool ieee80211_invoke_fast_rx(struct ieee80211_rx_data *rx,
 		u8 sa[ETH_ALEN];
 	} addrs __aligned(2);
 	struct ieee80211_sta_rx_stats *stats;
+	u32 encoded_rate;

 	/* for parallel-rx, we need to have DUP_VALIDATED, otherwise we write
 	 * to a common data structure; drivers can implement that per queue
@@ -5090,11 +5091,14 @@ static bool ieee80211_invoke_fast_rx(struct ieee80211_rx_data *rx,
 	/* push the addresses in front */
 	memcpy(skb_push(skb, sizeof(addrs)), &addrs, sizeof(addrs));

+	/* capture before mesh forward may memset or free skb->cb */
+	encoded_rate = sta_stats_encode_rate(status);
+
 	res = ieee80211_rx_mesh_data(rx->sdata, rx->sta, rx->skb);
 	switch (res) {
 	case RX_QUEUED:
 		stats->last_rx = jiffies;
-		stats->last_rate = sta_stats_encode_rate(status);
+		stats->last_rate = encoded_rate;
 		return true;
 	case RX_CONTINUE:
 		break;
--
2.50.1