mac80211: always allocate struct ieee802_11_elems

As the 802.11 spec evolves, we need to parse more and more
elements. This is causing the struct to grow, and we can no
longer get away with putting it on the stack.

Change the API to always dynamically allocate and return an
allocated pointer that must be kfree()d later.

As an alternative, I contemplated a scheme whereby we'd say
in the code which elements we needed, e.g.

    DECLARE_ELEMENT_PARSER(elems,
                           SUPPORTED_CHANNELS,
                           CHANNEL_SWITCH,
                           EXT(KEY_DELIVERY));

    ieee802_11_parse_elems(..., &elems, ...);

and while I think this is possible and will save us a lot
since most individual places only care about a small subset
of the elements, it ended up being a bit more work since a
lot of places do the parsing and then pass the struct to
other functions, sometimes with multiple levels.

Link: https://lore.kernel.org/r/20210920154009.26caff6b5998.I05ae58768e990e611aee8eca8abefd9d7bc15e05@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index 6b50cb5e0e3c..5e6b275afc9e 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -9,7 +9,7 @@
  * Copyright 2007, Michael Wu <flamingice@sourmilk.net>
  * Copyright 2013-2015  Intel Mobile Communications GmbH
  * Copyright 2016-2017  Intel Deutschland GmbH
- * Copyright (C) 2018-2020 Intel Corporation
+ * Copyright (C) 2018-2021 Intel Corporation
  */
 
 #include <linux/if_arp.h>
@@ -155,7 +155,7 @@ ieee80211_bss_info_update(struct ieee80211_local *local,
 	};
 	bool signal_valid;
 	struct ieee80211_sub_if_data *scan_sdata;
-	struct ieee802_11_elems elems;
+	struct ieee802_11_elems *elems;
 	size_t baselen;
 	u8 *elements;
 
@@ -209,8 +209,10 @@ ieee80211_bss_info_update(struct ieee80211_local *local,
 	if (baselen > len)
 		return NULL;
 
-	ieee802_11_parse_elems(elements, len - baselen, false, &elems,
-			       mgmt->bssid, cbss->bssid);
+	elems = ieee802_11_parse_elems(elements, len - baselen, false,
+				       mgmt->bssid, cbss->bssid);
+	if (!elems)
+		return NULL;
 
 	/* In case the signal is invalid update the status */
 	signal_valid = channel == cbss->channel;
@@ -218,15 +220,17 @@ ieee80211_bss_info_update(struct ieee80211_local *local,
 		rx_status->flag |= RX_FLAG_NO_SIGNAL_VAL;
 
 	bss = (void *)cbss->priv;
-	ieee80211_update_bss_from_elems(local, bss, &elems, rx_status, beacon);
+	ieee80211_update_bss_from_elems(local, bss, elems, rx_status, beacon);
 
 	list_for_each_entry(non_tx_cbss, &cbss->nontrans_list, nontrans_list) {
 		non_tx_bss = (void *)non_tx_cbss->priv;
 
-		ieee80211_update_bss_from_elems(local, non_tx_bss, &elems,
+		ieee80211_update_bss_from_elems(local, non_tx_bss, elems,
 						rx_status, beacon);
 	}
 
+	kfree(elems);
+
 	return bss;
 }