wifi: b43legacy: enforce bounds check on firmware key index in RX path

commit a035766 upstream.

Same fix as b43: the firmware-controlled key index in b43legacy_rx()
can exceed dev->max_nr_keys. The existing B43legacy_WARN_ON is
non-enforcing in production builds, allowing an out-of-bounds read of
dev->key[].

Make the check enforcing by dropping the frame for invalid indices.

Fixes: 75388ac ("[B43LEGACY]: add mac80211-based driver for legacy BCM43xx devices")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
Link: https://patch.msgid.link/20260417111145.2694196-2-tristmd@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Tristan Madani

drivers/net/wireless/broadcom/b43legacy/xmit.c

@@ -476,7 +476,8 @@ void b43legacy_rx(struct b43legacy_wldev *dev,
 		 * key index, but the ucode passed it slightly different.
 		 */
 		keyidx = b43legacy_kidx_to_raw(dev, keyidx);
-		B43legacy_WARN_ON(keyidx >= dev->max_nr_keys);
+		if (B43legacy_WARN_ON(keyidx >= dev->max_nr_keys))
+			goto drop;
 
 		if (dev->key[keyidx].algorithm != B43legacy_SEC_ALGO_NONE) {
 			/* Remove PROTECTED flag to mark it as decrypted. */