From 7fec9e7bc1027bc7da10e0289178cd7c785c0b5b Mon Sep 17 00:00:00 2001
From: Benjamin Berg <benjamin.berg@intel.com>
Date: Thu, 28 Dec 2023 15:14:05 +0200
Subject: [PATCH] nl80211: Retrieve maxattr via genl for nl80211

Older kernel versions may not support all attributes and may refuse
commands that include them. To avoid sending too new attributes query
the highest supported attribute. This allows adding appropriate checks
where needed.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
---
 src/drivers/driver_nl80211.c | 28 ++++++++++++++++++++++++++++
 src/drivers/driver_nl80211.h |  1 +
 2 files changed, 29 insertions(+)

diff --git a/src/drivers/driver_nl80211.c b/src/drivers/driver_nl80211.c
index 39c9362d0..8313ac594 100644
--- a/src/drivers/driver_nl80211.c
+++ b/src/drivers/driver_nl80211.c
@@ -16,6 +16,7 @@
 #include <net/if.h>
 #include <netlink/genl/genl.h>
 #include <netlink/genl/ctrl.h>
+#include <netlink/genl/family.h>
 #ifdef CONFIG_LIBNL3_ROUTE
 #include <netlink/route/neighbour.h>
 #endif /* CONFIG_LIBNL3_ROUTE */
@@ -1938,6 +1939,8 @@ static int wpa_driver_nl80211_get_country(void *priv, char *alpha2)
 
 static int wpa_driver_nl80211_init_nl_global(struct nl80211_global *global)
 {
+	struct nl_cache *cache = NULL;
+	struct genl_family *family = NULL;
 	int ret;
 
 	global->nl_cb = nl_cb_alloc(NL_CB_DEFAULT);
@@ -2009,6 +2012,29 @@ static int wpa_driver_nl80211_init_nl_global(struct nl80211_global *global)
 		/* Continue without vendor events */
 	}
 
+	/* Resolve maxattr for kernel support checks */
+	ret = genl_ctrl_alloc_cache(global->nl, &cache);
+	if (ret < 0) {
+		wpa_printf(MSG_DEBUG,
+			   "nl80211: Could not allocate genl cache: %d (%s)",
+			   ret, nl_geterror(ret));
+		goto err;
+	}
+
+	family = genl_ctrl_search(cache, global->nl80211_id);
+	if (!family) {
+		wpa_printf(MSG_DEBUG,
+			   "nl80211: Could not get nl80211 family from cache: %d (%s)",
+			   ret, nl_geterror(ret));
+		goto err;
+	}
+
+	global->nl80211_maxattr = genl_family_get_maxattr(family);
+	wpa_printf(MSG_DEBUG, "nl80211: Maximum supported attribute ID: %u",
+		   global->nl80211_maxattr);
+	genl_family_put(family);
+	nl_cache_free(cache);
+
 	nl_cb_set(global->nl_cb, NL_CB_SEQ_CHECK, NL_CB_CUSTOM,
 		  no_seq_check, NULL);
 	nl_cb_set(global->nl_cb, NL_CB_VALID, NL_CB_CUSTOM,
@@ -2021,6 +2047,8 @@ static int wpa_driver_nl80211_init_nl_global(struct nl80211_global *global)
 	return 0;
 
 err:
+	genl_family_put(family);
+	nl_cache_free(cache);
 	nl_destroy_handles(&global->nl_event);
 	nl_destroy_handles(&global->nl);
 	nl_cb_put(global->nl_cb);
diff --git a/src/drivers/driver_nl80211.h b/src/drivers/driver_nl80211.h
index 2b2bc9b11..1eb5656ff 100644
--- a/src/drivers/driver_nl80211.h
+++ b/src/drivers/driver_nl80211.h
@@ -32,6 +32,7 @@ struct nl80211_global {
 	struct nl_cb *nl_cb;
 	struct nl_sock *nl;
 	int nl80211_id;
+	unsigned int nl80211_maxattr;
 	int nlctrl_id;
 	int ioctl_sock; /* socket for ioctl() use */