[RFC PATCH 1/2] net: extend drop reasons for multiple subsystems

[RFC PATCH 1/2] net: extend drop reasons for multiple subsystems

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

Extend drop reasons to make them usable by subsystems
other than core by reserving the high 16 bits for a
new subsystem ID, of which 0 of course is used for the
existing reasons immediately.

To still be able to have string reasons, restructure
that code a bit to make the loopup under RCU, the only
user of this (right now) is drop_monitor.

Link: https://lore.kernel.org/netdev/00659771ed54353f92027702c5bbb84702da62ce.camel@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 include/net/dropreason.h | 34 +++++++++++++++++++++----
 net/core/drop_monitor.c  | 32 +++++++++++++++++-------
 net/core/skbuff.c        | 54 +++++++++++++++++++++++++++++++++++++---
 3 files changed, 103 insertions(+), 17 deletions(-)

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index c0a3ea806cd5..0f9508c6a34f 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -338,11 +338,24 @@ enum skb_drop_reason {
 	 * for another host.
 	 */
 	SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST,
-	/**
-	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
-	 * used as a real 'reason'
+
+	/** @SKB_DROP_REASON_SUBSYS_MASK: subsystem mask in drop reasons,
+	 * see &enum skb_drop_reason_subsys
 	 */
-	SKB_DROP_REASON_MAX,
+	SKB_DROP_REASON_SUBSYS_MASK = 0xffff0000,
+};
+
+#define SKB_DROP_REASON_SUBSYS_SHIFT	16
+
+/**
+ * enum skb_drop_reason_subsys - subsystem tag for (extended) drop reasons
+ */
+enum skb_drop_reason_subsys {
+	/** @SKB_DROP_REASON_SUBSYS_CORE: core drop reasons defined above */
+	SKB_DROP_REASON_SUBSYS_CORE,
+
+	/** @SKB_DROP_REASON_SUBSYS_NUM: number of subsystems defined */
+	SKB_DROP_REASON_SUBSYS_NUM
 };
 
 #define SKB_DR_INIT(name, reason)				\
@@ -358,6 +371,17 @@ enum skb_drop_reason {
 			SKB_DR_SET(name, reason);		\
 	} while (0)
 
-extern const char * const drop_reasons[];
+struct drop_reason_list {
+	const char * const *reasons;
+	size_t n_reasons;
+};
+
+/* Note: due to dynamic registrations, access must be under RCU */
+extern const struct drop_reason_list __rcu *
+drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
+
+void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
+				  const struct drop_reason_list *list);
+void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys);
 
 #endif
diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 5a782d1d8fd3..c6c60dc75b2d 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -21,6 +21,7 @@
 #include <linux/workqueue.h>
 #include <linux/netlink.h>
 #include <linux/net_dropmon.h>
+#include <linux/bitfield.h>
 #include <linux/percpu.h>
 #include <linux/timer.h>
 #include <linux/bitops.h>
@@ -504,8 +505,6 @@ static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
 	if (!nskb)
 		return;
 
-	if (unlikely(reason >= SKB_DROP_REASON_MAX || reason <= 0))
-		reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	cb = NET_DM_SKB_CB(nskb);
 	cb->reason = reason;
 	cb->pc = location;
@@ -552,9 +551,9 @@ static size_t net_dm_in_port_size(void)
 }
 
 #define NET_DM_MAX_SYMBOL_LEN 40
+#define NET_DM_MAX_REASON_LEN 50
 
-static size_t net_dm_packet_report_size(size_t payload_len,
-					enum skb_drop_reason reason)
+static size_t net_dm_packet_report_size(size_t payload_len)
 {
 	size_t size;
 
@@ -576,7 +575,7 @@ static size_t net_dm_packet_report_size(size_t payload_len,
 	       /* NET_DM_ATTR_PROTO */
 	       nla_total_size(sizeof(u16)) +
 	       /* NET_DM_ATTR_REASON */
-	       nla_total_size(strlen(drop_reasons[reason]) + 1) +
+	       nla_total_size(NET_DM_MAX_REASON_LEN + 1) +
 	       /* NET_DM_ATTR_PAYLOAD */
 	       nla_total_size(payload_len);
 }
@@ -610,6 +609,8 @@ static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
 				     size_t payload_len)
 {
 	struct net_dm_skb_cb *cb = NET_DM_SKB_CB(skb);
+	const struct drop_reason_list *list = NULL;
+	unsigned int subsys, subsys_reason;
 	char buf[NET_DM_MAX_SYMBOL_LEN];
 	struct nlattr *attr;
 	void *hdr;
@@ -627,9 +628,24 @@ static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
 			      NET_DM_ATTR_PAD))
 		goto nla_put_failure;
 
+	rcu_read_lock();
+	subsys = u32_get_bits(cb->reason, SKB_DROP_REASON_SUBSYS_MASK);
+	if (subsys < SKB_DROP_REASON_SUBSYS_NUM)
+		list = rcu_dereference(drop_reasons_by_subsys[subsys]);
+	subsys_reason = cb->reason & ~SKB_DROP_REASON_SUBSYS_MASK;
+	if (!list ||
+	    subsys_reason >= list->n_reasons ||
+	    !list->reasons[subsys_reason] ||
+	    strlen(list->reasons[subsys_reason]) > NET_DM_MAX_REASON_LEN) {
+		list = rcu_dereference(drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_CORE]);
+		subsys_reason = SKB_DROP_REASON_NOT_SPECIFIED;
+	}
 	if (nla_put_string(msg, NET_DM_ATTR_REASON,
-			   drop_reasons[cb->reason]))
+			   list->reasons[subsys_reason])) {
+		rcu_read_unlock();
 		goto nla_put_failure;
+	}
+	rcu_read_unlock();
 
 	snprintf(buf, sizeof(buf), "%pS", cb->pc);
 	if (nla_put_string(msg, NET_DM_ATTR_SYMBOL, buf))
@@ -687,9 +703,7 @@ static void net_dm_packet_report(struct sk_buff *skb)
 	if (net_dm_trunc_len)
 		payload_len = min_t(size_t, net_dm_trunc_len, payload_len);
 
-	msg = nlmsg_new(net_dm_packet_report_size(payload_len,
-						  NET_DM_SKB_CB(skb)->reason),
-			GFP_KERNEL);
+	msg = nlmsg_new(net_dm_packet_report_size(payload_len), GFP_KERNEL);
 	if (!msg)
 		goto out;
 
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 050a875d09c5..62bf5a756258 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -122,11 +122,59 @@ EXPORT_SYMBOL(sysctl_max_skb_frags);
 
 #undef FN
 #define FN(reason) [SKB_DROP_REASON_##reason] = #reason,
-const char * const drop_reasons[] = {
+static const char * const drop_reasons[] = {
 	[SKB_CONSUMED] = "CONSUMED",
 	DEFINE_DROP_REASON(FN, FN)
 };
-EXPORT_SYMBOL(drop_reasons);
+
+static const struct drop_reason_list drop_reasons_core = {
+	.reasons = drop_reasons,
+	.n_reasons = ARRAY_SIZE(drop_reasons),
+};
+
+const struct drop_reason_list __rcu *
+drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
+	[SKB_DROP_REASON_SUBSYS_CORE] = &drop_reasons_core,
+};
+EXPORT_SYMBOL(drop_reasons_by_subsys);
+
+/**
+ * drop_reasons_register_subsys - register another drop reason subsystem
+ * @subsys: the subsystem to register, must not be the core
+ * @list: the list of drop reasons within the subsystem, must point to
+ *	a statically initialized list
+ */
+void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
+				  const struct drop_reason_list *list)
+{
+	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
+		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
+		 "invalid subsystem %d\n", subsys))
+		return;
+
+	/* must point to statically allocated memory, so INIT is OK */
+	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], list);
+}
+EXPORT_SYMBOL_GPL(drop_reasons_register_subsys);
+
+/**
+ * drop_reasons_unregister_subsys - unregister a drop reason subsystem
+ * @subsys: the subsystem to remove, must not be the core
+ *
+ * Note: This will synchronize_rcu() to ensure no users when it returns.
+ */
+void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys)
+{
+	if (WARN(subsys <= SKB_DROP_REASON_SUBSYS_CORE ||
+		 subsys >= ARRAY_SIZE(drop_reasons_by_subsys),
+		 "invalid subsystem %d\n", subsys))
+		return;
+
+	RCU_INIT_POINTER(drop_reasons_by_subsys[subsys], NULL);
+
+	synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(drop_reasons_unregister_subsys);
 
 /**
  *	skb_panic - private function for out-of-line support
@@ -984,7 +1032,7 @@ bool __kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
 	if (unlikely(!skb_unref(skb)))
 		return false;
 
-	DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);
+	DEBUG_NET_WARN_ON_ONCE(reason == SKB_NOT_DROPPED_YET);
 
 	if (reason == SKB_CONSUMED)
 		trace_consume_skb(skb, __builtin_return_address(0));
-- 
2.39.2

[RFC PATCH 2/2] mac80211: use the new drop reasons infrastructure

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

It can be really hard to analyse or debug why packets are
going missing in mac80211, so add the needed infrastructure
to use use the new per-subsystem drop reasons.

We actually use two drop reason subsystems here because of
the different handling of frames that are dropped but still
go to monitor for old versions of hostapd, and those that
are just completely unusable (e.g. crypto failed.)

Annotate a few reasons here just to illustrate this, we'll
need to go through and annotate more of them later.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 include/net/dropreason.h   | 10 +++++++
 net/mac80211/drop.h        | 55 ++++++++++++++++++++++++++++++++++
 net/mac80211/ieee80211_i.h |  8 +----
 net/mac80211/main.c        | 30 +++++++++++++++++++
 net/mac80211/rx.c          | 61 ++++++++++++++++++--------------------
 net/mac80211/wpa.c         | 24 +++++++--------
 6 files changed, 137 insertions(+), 51 deletions(-)
 create mode 100644 net/mac80211/drop.h

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index 0f9508c6a34f..98be6ebbef37 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -354,6 +354,16 @@ enum skb_drop_reason_subsys {
 	/** @SKB_DROP_REASON_SUBSYS_CORE: core drop reasons defined above */
 	SKB_DROP_REASON_SUBSYS_CORE,
 
+	/** @SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE: mac80211 drop reasons
+	 * for unusable frames, see net/mac80211/drop.h
+	 */
+	SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE,
+
+	/** @SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR: mac80211 drop reasons
+	 * for frames still going to monitor, see net/mac80211/drop.h
+	 */
+	SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR,
+
 	/** @SKB_DROP_REASON_SUBSYS_NUM: number of subsystems defined */
 	SKB_DROP_REASON_SUBSYS_NUM
 };
diff --git a/net/mac80211/drop.h b/net/mac80211/drop.h
new file mode 100644
index 000000000000..45550111613c
--- /dev/null
+++ b/net/mac80211/drop.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * mac80211 drop reason list
+ *
+ * Copyright (C) 2023 Intel Corporation
+ */
+
+#ifndef MAC80211_DROPS_H
+#define MAC80211_DROPS_H
+
+typedef unsigned int __bitwise ieee80211_rx_result;
+
+#define MAC80211_DROP_REASONS_MONITOR(R)	\
+	R(RX_DROP_M_4ADDR_NDP)			\
+	R(RX_DROP_M_BAD_BCN_KEYIDX)		\
+	R(RX_DROP_M_BAD_MGMT_KEYIDX)		\
+/* this line for the trailing \ - add before this */
+
+#define MAC80211_DROP_REASONS_UNUSABLE(R)	\
+	R(RX_DROP_U_MIC_FAIL)			\
+	R(RX_DROP_U_REPLAY)			\
+	R(RX_DROP_U_BAD_MMIE)			\
+/* this line for the trailing \ - add before this */
+
+/* having two enums allows for checking ieee80211_rx_result use with sparse */
+enum ___mac80211_drop_reason {
+/* if we get to the end of handlers with RX_CONTINUE this will be the reason */
+	___RX_CONTINUE	= SKB_CONSUMED,
+
+/* this never gets used as an argument to kfree_skb_reason() */
+	___RX_QUEUED	= SKB_NOT_DROPPED_YET,
+
+#define ENUM(x) ___ ## x,
+	___RX_DROP_MONITOR = SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR <<
+		SKB_DROP_REASON_SUBSYS_SHIFT,
+	MAC80211_DROP_REASONS_MONITOR(ENUM)
+
+	___RX_DROP_UNUSABLE = SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE <<
+		SKB_DROP_REASON_SUBSYS_SHIFT,
+	MAC80211_DROP_REASONS_UNUSABLE(ENUM)
+#undef ENUM
+};
+
+enum mac80211_drop_reason {
+	RX_CONTINUE	 = (__force ieee80211_rx_result)___RX_CONTINUE,
+	RX_QUEUED	 = (__force ieee80211_rx_result)___RX_QUEUED,
+	RX_DROP_MONITOR	 = (__force ieee80211_rx_result)___RX_DROP_MONITOR,
+	RX_DROP_UNUSABLE = (__force ieee80211_rx_result)___RX_DROP_UNUSABLE,
+#define DEF(x) x = (__force ieee80211_rx_result)___ ## x,
+	MAC80211_DROP_REASONS_MONITOR(DEF)
+	MAC80211_DROP_REASONS_UNUSABLE(DEF)
+#undef DEF
+};
+
+#endif /* MAC80211_DROPS_H */
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 85ecbf57d64e..42e79edfaf74 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -33,6 +33,7 @@
 #include "key.h"
 #include "sta_info.h"
 #include "debug.h"
+#include "drop.h"
 
 extern const struct cfg80211_ops mac80211_config_ops;
 
@@ -170,13 +171,6 @@ struct ieee80211_tx_data {
 	unsigned int flags;
 };
 
-
-typedef unsigned __bitwise ieee80211_rx_result;
-#define RX_CONTINUE		((__force ieee80211_rx_result) 0u)
-#define RX_DROP_UNUSABLE	((__force ieee80211_rx_result) 1u)
-#define RX_DROP_MONITOR		((__force ieee80211_rx_result) 2u)
-#define RX_QUEUED		((__force ieee80211_rx_result) 3u)
-
 /**
  * enum ieee80211_packet_rx_flags - packet RX flags
  * @IEEE80211_RX_AMSDU: a-MSDU packet
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 846528850612..4b3c07bc9d02 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -1540,6 +1540,28 @@ void ieee80211_free_hw(struct ieee80211_hw *hw)
 }
 EXPORT_SYMBOL(ieee80211_free_hw);
 
+static const char * const drop_reasons_monitor[] = {
+#define V(x)	#x,
+	[0] = "RX_DROP_MONITOR",
+	MAC80211_DROP_REASONS_MONITOR(V)
+};
+
+static struct drop_reason_list drop_reason_list_monitor = {
+	.reasons = drop_reasons_monitor,
+	.n_reasons = ARRAY_SIZE(drop_reasons_monitor),
+};
+
+static const char * const drop_reasons_unusable[] = {
+	[0] = "RX_DROP_UNUSABLE",
+	MAC80211_DROP_REASONS_UNUSABLE(V)
+#undef V
+};
+
+static struct drop_reason_list drop_reason_list_unusable = {
+	.reasons = drop_reasons_unusable,
+	.n_reasons = ARRAY_SIZE(drop_reasons_unusable),
+};
+
 static int __init ieee80211_init(void)
 {
 	struct sk_buff *skb;
@@ -1557,6 +1579,11 @@ static int __init ieee80211_init(void)
 	if (ret)
 		goto err_netdev;
 
+	drop_reasons_register_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR,
+				     &drop_reason_list_monitor);
+	drop_reasons_register_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE,
+				     &drop_reason_list_unusable);
+
 	return 0;
  err_netdev:
 	rc80211_minstrel_exit();
@@ -1572,6 +1599,9 @@ static void __exit ieee80211_exit(void)
 
 	ieee80211_iface_exit();
 
+	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR);
+	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE);
+
 	rcu_barrier();
 }
 
diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 1c957194554b..e8d482a830ac 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1826,7 +1826,7 @@ ieee80211_rx_h_sta_process(struct ieee80211_rx_data *rx)
 				cfg80211_rx_unexpected_4addr_frame(
 					rx->sdata->dev, sta->sta.addr,
 					GFP_ATOMIC);
-			return RX_DROP_MONITOR;
+			return RX_DROP_M_4ADDR_NDP;
 		}
 		/*
 		 * Update counter and free packet here to avoid
@@ -1961,7 +1961,7 @@ ieee80211_rx_h_decrypt(struct ieee80211_rx_data *rx)
 				cfg80211_rx_unprot_mlme_mgmt(rx->sdata->dev,
 							     skb->data,
 							     skb->len);
-			return RX_DROP_MONITOR; /* unexpected BIP keyidx */
+			return RX_DROP_M_BAD_BCN_KEYIDX;
 		}
 
 		rx->key = ieee80211_rx_get_bigtk(rx, mmie_keyidx);
@@ -1975,7 +1975,7 @@ ieee80211_rx_h_decrypt(struct ieee80211_rx_data *rx)
 
 		if (mmie_keyidx < NUM_DEFAULT_KEYS ||
 		    mmie_keyidx >= NUM_DEFAULT_KEYS + NUM_DEFAULT_MGMT_KEYS)
-			return RX_DROP_MONITOR; /* unexpected BIP keyidx */
+			return RX_DROP_M_BAD_MGMT_KEYIDX; /* unexpected BIP keyidx */
 		if (rx->link_sta) {
 			if (ieee80211_is_group_privacy_action(skb) &&
 			    test_sta_flag(rx->sta, WLAN_STA_MFP))
@@ -3957,7 +3957,8 @@ ieee80211_rx_h_mgmt(struct ieee80211_rx_data *rx)
 }
 
 static void ieee80211_rx_cooked_monitor(struct ieee80211_rx_data *rx,
-					struct ieee80211_rate *rate)
+					struct ieee80211_rate *rate,
+					ieee80211_rx_result reason)
 {
 	struct ieee80211_sub_if_data *sdata;
 	struct ieee80211_local *local = rx->local;
@@ -4021,42 +4022,38 @@ static void ieee80211_rx_cooked_monitor(struct ieee80211_rx_data *rx,
 	}
 
  out_free_skb:
-	dev_kfree_skb(skb);
+	kfree_skb_reason(skb, (__force u32)reason);
 }
 
 static void ieee80211_rx_handlers_result(struct ieee80211_rx_data *rx,
 					 ieee80211_rx_result res)
 {
-	switch (res) {
-	case RX_DROP_MONITOR:
-		I802_DEBUG_INC(rx->sdata->local->rx_handlers_drop);
-		if (rx->sta)
-			rx->link_sta->rx_stats.dropped++;
-		fallthrough;
-	case RX_CONTINUE: {
-		struct ieee80211_rate *rate = NULL;
-		struct ieee80211_supported_band *sband;
-		struct ieee80211_rx_status *status;
+	struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(rx->skb);
+	struct ieee80211_supported_band *sband;
+	struct ieee80211_rate *rate = NULL;
 
-		status = IEEE80211_SKB_RXCB((rx->skb));
-
-		sband = rx->local->hw.wiphy->bands[status->band];
-		if (status->encoding == RX_ENC_LEGACY)
-			rate = &sband->bitrates[status->rate_idx];
-
-		ieee80211_rx_cooked_monitor(rx, rate);
-		break;
-		}
-	case RX_DROP_UNUSABLE:
-		I802_DEBUG_INC(rx->sdata->local->rx_handlers_drop);
-		if (rx->sta)
-			rx->link_sta->rx_stats.dropped++;
-		dev_kfree_skb(rx->skb);
-		break;
-	case RX_QUEUED:
+	if (res == RX_QUEUED) {
 		I802_DEBUG_INC(rx->sdata->local->rx_handlers_queued);
-		break;
+		return;
 	}
+
+	if (res != RX_CONTINUE) {
+		I802_DEBUG_INC(rx->sdata->local->rx_handlers_drop);
+		if (rx->sta)
+			rx->link_sta->rx_stats.dropped++;
+	}
+
+	if (u32_get_bits((__force u32)res, SKB_DROP_REASON_SUBSYS_MASK) ==
+			SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE) {
+		kfree_skb_reason(rx->skb, (__force u32)res);
+		return;
+	}
+
+	sband = rx->local->hw.wiphy->bands[status->band];
+	if (status->encoding == RX_ENC_LEGACY)
+		rate = &sband->bitrates[status->rate_idx];
+
+	ieee80211_rx_cooked_monitor(rx, rate, res);
 }
 
 static void ieee80211_rx_handlers(struct ieee80211_rx_data *rx,
diff --git a/net/mac80211/wpa.c b/net/mac80211/wpa.c
index 20f742b5503b..4133496da378 100644
--- a/net/mac80211/wpa.c
+++ b/net/mac80211/wpa.c
@@ -550,7 +550,7 @@ ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx,
 		if (res < 0 ||
 		    (!res && !(status->flag & RX_FLAG_ALLOW_SAME_PN))) {
 			key->u.ccmp.replays++;
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_REPLAY;
 		}
 
 		if (!(status->flag & RX_FLAG_DECRYPTED)) {
@@ -564,7 +564,7 @@ ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx,
 				    skb->data + hdrlen + IEEE80211_CCMP_HDR_LEN,
 				    data_len,
 				    skb->data + skb->len - mic_len))
-				return RX_DROP_UNUSABLE;
+				return RX_DROP_U_MIC_FAIL;
 		}
 
 		memcpy(key->u.ccmp.rx_pn[queue], pn, IEEE80211_CCMP_PN_LEN);
@@ -746,7 +746,7 @@ ieee80211_crypto_gcmp_decrypt(struct ieee80211_rx_data *rx)
 		if (res < 0 ||
 		    (!res && !(status->flag & RX_FLAG_ALLOW_SAME_PN))) {
 			key->u.gcmp.replays++;
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_REPLAY;
 		}
 
 		if (!(status->flag & RX_FLAG_DECRYPTED)) {
@@ -761,7 +761,7 @@ ieee80211_crypto_gcmp_decrypt(struct ieee80211_rx_data *rx)
 				    data_len,
 				    skb->data + skb->len -
 				    IEEE80211_GCMP_MIC_LEN))
-				return RX_DROP_UNUSABLE;
+				return RX_DROP_U_MIC_FAIL;
 		}
 
 		memcpy(key->u.gcmp.rx_pn[queue], pn, IEEE80211_GCMP_PN_LEN);
@@ -930,13 +930,13 @@ ieee80211_crypto_aes_cmac_decrypt(struct ieee80211_rx_data *rx)
 		(skb->data + skb->len - sizeof(*mmie));
 	if (mmie->element_id != WLAN_EID_MMIE ||
 	    mmie->length != sizeof(*mmie) - 2)
-		return RX_DROP_UNUSABLE; /* Invalid MMIE */
+		return RX_DROP_U_BAD_MMIE; /* Invalid MMIE */
 
 	bip_ipn_swap(ipn, mmie->sequence_number);
 
 	if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
 		key->u.aes_cmac.replays++;
-		return RX_DROP_UNUSABLE;
+		return RX_DROP_U_REPLAY;
 	}
 
 	if (!(status->flag & RX_FLAG_DECRYPTED)) {
@@ -946,7 +946,7 @@ ieee80211_crypto_aes_cmac_decrypt(struct ieee80211_rx_data *rx)
 				   skb->data + 24, skb->len - 24, mic);
 		if (crypto_memneq(mic, mmie->mic, sizeof(mmie->mic))) {
 			key->u.aes_cmac.icverrors++;
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_MIC_FAIL;
 		}
 	}
 
@@ -986,7 +986,7 @@ ieee80211_crypto_aes_cmac_256_decrypt(struct ieee80211_rx_data *rx)
 
 	if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
 		key->u.aes_cmac.replays++;
-		return RX_DROP_UNUSABLE;
+		return RX_DROP_U_REPLAY;
 	}
 
 	if (!(status->flag & RX_FLAG_DECRYPTED)) {
@@ -996,7 +996,7 @@ ieee80211_crypto_aes_cmac_256_decrypt(struct ieee80211_rx_data *rx)
 				       skb->data + 24, skb->len - 24, mic);
 		if (crypto_memneq(mic, mmie->mic, sizeof(mmie->mic))) {
 			key->u.aes_cmac.icverrors++;
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_MIC_FAIL;
 		}
 	}
 
@@ -1079,13 +1079,13 @@ ieee80211_crypto_aes_gmac_decrypt(struct ieee80211_rx_data *rx)
 		(skb->data + skb->len - sizeof(*mmie));
 	if (mmie->element_id != WLAN_EID_MMIE ||
 	    mmie->length != sizeof(*mmie) - 2)
-		return RX_DROP_UNUSABLE; /* Invalid MMIE */
+		return RX_DROP_U_BAD_MMIE; /* Invalid MMIE */
 
 	bip_ipn_swap(ipn, mmie->sequence_number);
 
 	if (memcmp(ipn, key->u.aes_gmac.rx_pn, 6) <= 0) {
 		key->u.aes_gmac.replays++;
-		return RX_DROP_UNUSABLE;
+		return RX_DROP_U_REPLAY;
 	}
 
 	if (!(status->flag & RX_FLAG_DECRYPTED)) {
@@ -1104,7 +1104,7 @@ ieee80211_crypto_aes_gmac_decrypt(struct ieee80211_rx_data *rx)
 		    crypto_memneq(mic, mmie->mic, sizeof(mmie->mic))) {
 			key->u.aes_gmac.icverrors++;
 			kfree(mic);
-			return RX_DROP_UNUSABLE;
+			return RX_DROP_U_MIC_FAIL;
 		}
 		kfree(mic);
 	}
-- 
2.39.2

Re: [RFC PATCH 2/2] mac80211: use the new drop reasons infrastructure

[Johannes Berg]

Couple of comments that I didn't want to inline into the patch...

> 
> +	/** @SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE: mac80211 drop reasons
> +	 * for unusable frames, see net/mac80211/drop.h

Not sure if that should be in net/mac80211/drop.h, or better
include/net/mac80211-drop.h or something.

> +static const char * const drop_reasons_monitor[] = {
> +#define V(x)	#x,
> +	[0] = "RX_DROP_MONITOR",
> +	MAC80211_DROP_REASONS_MONITOR(V)

We could, and perhaps should, add some prefix here, so the strings
become something like SKB_DROP_REASON_MAC80211_MONITOR_...

The only annoying thing with that is we'd probably then want to generate
the "RX_DROP_M_" prefix for the constants in the DEF() macros in the
header file, which might make elixir/ctags/... even worse - but it's
probably already pretty bad for it anyway.

> +	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR);
> +	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE);
> +
>  	rcu_barrier();

This is making me think that perhaps we don't want synchronize_rcu()
inside drop_reasons_unregister_subsys(), since I have two now and also
already have an rcu_barrier() ... so maybe just document that it's
needed?

> +++ b/net/mac80211/rx.c
> @@ -1826,7 +1826,7 @@ ieee80211_rx_h_sta_process(struct ieee80211_rx_data *rx)
>  				cfg80211_rx_unexpected_4addr_frame(
>  					rx->sdata->dev, sta->sta.addr,
>  					GFP_ATOMIC);
> -			return RX_DROP_MONITOR;
> +			return RX_DROP_M_4ADDR_NDP;

This was coded up too hastily, it should've been called
RX_DROP_M_UNEXPECTED_4ADDR.

> +++ b/net/mac80211/wpa.c
> @@ -550,7 +550,7 @@ ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx,
>  		if (res < 0 ||
>  		    (!res && !(status->flag & RX_FLAG_ALLOW_SAME_PN))) {
>  			key->u.ccmp.replays++;
> -			return RX_DROP_UNUSABLE;
> +			return RX_DROP_U_REPLAY;

I did wonder if we should distinguish CCMP/GCMP/... for replays, MIC
failures etc., but haven't really quite decided yet. With drop_monitor
you'd have the frame (I think?) and that makes it easy to see what it
was. It's also not really all that relevant for the drop reasons
infrastructure discussion.

johannes

Re: [RFC PATCH 1/2] net: extend drop reasons for multiple subsystems

[Jakub Kicinski]

On Wed, 29 Mar 2023 23:46:19 +0200 Johannes Berg wrote:
> -	DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);
> +	DEBUG_NET_WARN_ON_ONCE(reason == SKB_NOT_DROPPED_YET);

We can still validate that the top bits are within known range 
of subsystems?

Re: [RFC PATCH 2/2] mac80211: use the new drop reasons infrastructure

[Jakub Kicinski]

On Wed, 29 Mar 2023 23:46:20 +0200 Johannes Berg wrote:
> +	/** @SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE: mac80211 drop reasons
> +	 * for unusable frames, see net/mac80211/drop.h
> +	 */
> +	SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE,
> +
> +	/** @SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR: mac80211 drop reasons
> +	 * for frames still going to monitor, see net/mac80211/drop.h
> +	 */
> +	SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR,

heh, didn't expect you'd have two different subsystems TBH

Re: [RFC PATCH 2/2] mac80211: use the new drop reasons infrastructure

[Jakub Kicinski]

On Wed, 29 Mar 2023 23:56:31 +0200 Johannes Berg wrote:
> > +	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR);
> > +	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE);
> > +
> >  	rcu_barrier();  
> 
> This is making me think that perhaps we don't want synchronize_rcu()
> inside drop_reasons_unregister_subsys(), since I have two now and also
> already have an rcu_barrier() ... so maybe just document that it's
> needed?

premature optimization? some workload is reloading mac80211 in a loop?

Re: [RFC PATCH 1/2] net: extend drop reasons for multiple subsystems

[Johannes Berg]

On Wed, 2023-03-29 at 21:05 -0700, Jakub Kicinski wrote:
> On Wed, 29 Mar 2023 23:46:19 +0200 Johannes Berg wrote:
> > -	DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);
> > +	DEBUG_NET_WARN_ON_ONCE(reason == SKB_NOT_DROPPED_YET);
> 
> We can still validate that the top bits are within known range 
> of subsystems?

Yeah, I was being a bit sneaky here ;)

We could, for sure. Given that the users should probably be defensively
coded anyway (as I did in drop_monitor), I wasn't sure if we _should_.

It seemed to me that for experimentation, especially if your driver is a
module, it might be easier to allow this?

That said, I don't have any strong feelings about it, and I have some
bugs here anyway so I can just add that.

We _could_ also keep a check for the core subsystem, but not sure that's
worth it?

johannes

Re: [RFC PATCH 2/2] mac80211: use the new drop reasons infrastructure

[Johannes Berg]

On Wed, 2023-03-29 at 21:05 -0700, Jakub Kicinski wrote:
> On Wed, 29 Mar 2023 23:46:20 +0200 Johannes Berg wrote:
> > +	/** @SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE: mac80211 drop reasons
> > +	 * for unusable frames, see net/mac80211/drop.h
> > +	 */
> > +	SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE,
> > +
> > +	/** @SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR: mac80211 drop reasons
> > +	 * for frames still going to monitor, see net/mac80211/drop.h
> > +	 */
> > +	SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR,
> 
> heh, didn't expect you'd have two different subsystems TBH
> 

Hah, me neither!

But then when I came to implement it, I wanted to use some bit in the
reason for he drop/unusable distinction. In fact I did that at first,
until I got to the string list, and realised that no matter how I sliced
it, I'd always have a very sparse array there. If I use the lowest bit
it'd be as compact as possible, but I'd expect the two spaces to not be
equivalently filled, so I'd still get a whole bunch NULLs in the array.

So then I switched to using two subsystems, since that way we have two
distinct string lists.

johannes

Re: [RFC PATCH 2/2] mac80211: use the new drop reasons infrastructure

[Johannes Berg]

On Wed, 2023-03-29 at 21:06 -0700, Jakub Kicinski wrote:
> On Wed, 29 Mar 2023 23:56:31 +0200 Johannes Berg wrote:
> > > +	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR);
> > > +	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE);
> > > +
> > >  	rcu_barrier();  
> > 
> > This is making me think that perhaps we don't want synchronize_rcu()
> > inside drop_reasons_unregister_subsys(), since I have two now and also
> > already have an rcu_barrier() ... so maybe just document that it's
> > needed?
> 
> premature optimization? some workload is reloading mac80211 in a loop?

Yeah, true, nobody is going to do that :-)

Let's leave it this way.

johannes

Re: [RFC PATCH 1/2] net: extend drop reasons for multiple subsystems

[Jakub Kicinski]

On Thu, 30 Mar 2023 10:11:12 +0200 Johannes Berg wrote:
> Yeah, I was being a bit sneaky here ;)
> 
> We could, for sure. Given that the users should probably be defensively
> coded anyway (as I did in drop_monitor), I wasn't sure if we _should_.
> 
> It seemed to me that for experimentation, especially if your driver is a
> module, it might be easier to allow this?
> 
> That said, I don't have any strong feelings about it, and I have some
> bugs here anyway so I can just add that.
> 
> We _could_ also keep a check for the core subsystem, but not sure that's
> worth it?

Checking the top bits should be good enough to catch uninitialized
values, and discourage out-of-tree shenanigans, I'd hope.