[PATCH net-next 10/15] batman-adv: annotate neigh_node last_seen with READ/WRITE_ONCE

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

The last_seen field for batadv_neigh_node tracks the jiffies value of the
most recent activity and is used to detect timeouts. These accesses are not
consistently protected by a lock, so READ_ONCE/WRITE_ONCE must be used to
prevent data races caused by compiler optimizations.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/bug/linux-6ad653e2-1ce9-4124-bdf2-2187de5a2c16
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/bat_iv_ogm.c | 4 ++--
 net/batman-adv/bat_v_elp.c  | 6 ++++--
 net/batman-adv/bat_v_ogm.c  | 2 +-
 net/batman-adv/originator.c | 4 ++--
 4 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index ee3a5ac465012..d4b6c09db8c7d 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -1169,7 +1169,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv,
 	if (!neigh_ifinfo)
 		goto out;
 
-	neigh_node->last_seen = jiffies;
+	WRITE_ONCE(neigh_node->last_seen, jiffies);
 
 	spin_lock_bh(&neigh_node->ifinfo_lock);
 	batadv_ring_buffer_set(neigh_ifinfo->bat_iv.tq_recv,
@@ -1289,7 +1289,7 @@ static bool batadv_iv_ogm_calc_tq(struct batadv_orig_node *orig_node,
 
 	/* if orig_node is direct neighbor update neigh_node last_seen */
 	if (orig_node == orig_neigh_node)
-		neigh_node->last_seen = jiffies;
+		WRITE_ONCE(neigh_node->last_seen, jiffies);
 
 	WRITE_ONCE(orig_node->last_seen, jiffies);
 
diff --git a/net/batman-adv/bat_v_elp.c b/net/batman-adv/bat_v_elp.c
index 6ad6042a5d9b6..cf84aed0c947e 100644
--- a/net/batman-adv/bat_v_elp.c
+++ b/net/batman-adv/bat_v_elp.c
@@ -506,6 +506,7 @@ static void batadv_v_elp_neigh_update(struct batadv_priv *bat_priv,
 	struct batadv_hardif_neigh_node *hardif_neigh;
 	struct batadv_orig_node *orig_neigh;
 	struct batadv_neigh_node *neigh;
+	unsigned long last_seen;
 	s32 elp_latest_seqno;
 	s32 seqno_diff;
 
@@ -531,8 +532,9 @@ static void batadv_v_elp_neigh_update(struct batadv_priv *bat_priv,
 	if (seqno_diff < 1 && seqno_diff > -BATADV_ELP_MAX_AGE)
 		goto hardif_free;
 
-	neigh->last_seen = jiffies;
-	hardif_neigh->last_seen = jiffies;
+	last_seen = jiffies;
+	WRITE_ONCE(neigh->last_seen, last_seen);
+	hardif_neigh->last_seen = last_seen;
 	hardif_neigh->bat_v.elp_latest_seqno = ntohl(elp_packet->seqno);
 	hardif_neigh->bat_v.elp_interval = ntohl(elp_packet->elp_interval);
 
diff --git a/net/batman-adv/bat_v_ogm.c b/net/batman-adv/bat_v_ogm.c
index 03c70d91e64d1..cf3c1d22761b9 100644
--- a/net/batman-adv/bat_v_ogm.c
+++ b/net/batman-adv/bat_v_ogm.c
@@ -658,7 +658,7 @@ static int batadv_v_ogm_metric_update(struct batadv_priv *bat_priv,
 		goto out;
 
 	last_seen = jiffies;
-	neigh_node->last_seen = last_seen;
+	WRITE_ONCE(neigh_node->last_seen, last_seen);
 	WRITE_ONCE(orig_node->last_seen, last_seen);
 
 	orig_ifinfo->last_real_seqno = ntohl(ogm2->seqno);
diff --git a/net/batman-adv/originator.c b/net/batman-adv/originator.c
index 3b925ba9c9723..352a88056e334 100644
--- a/net/batman-adv/originator.c
+++ b/net/batman-adv/originator.c
@@ -698,7 +698,7 @@ batadv_neigh_node_create(struct batadv_orig_node *orig_node,
 	kref_get(&hard_iface->refcount);
 	ether_addr_copy(neigh_node->addr, neigh_addr);
 	neigh_node->if_incoming = hard_iface;
-	neigh_node->last_seen = jiffies;
+	WRITE_ONCE(neigh_node->last_seen, jiffies);
 
 #ifdef CONFIG_BATMAN_ADV_BATMAN_V
 	ACCESS_PRIVATE(neigh_node, orig_node_id) = orig_node;
@@ -1126,7 +1126,7 @@ batadv_purge_orig_neighbors(struct batadv_priv *bat_priv,
 	/* for all neighbors towards this originator ... */
 	hlist_for_each_entry_safe(neigh_node, node_tmp,
 				  &orig_node->neigh_list, list) {
-		last_seen = neigh_node->last_seen;
+		last_seen = READ_ONCE(neigh_node->last_seen);
 		if_incoming = neigh_node->if_incoming;
 
 		if (batadv_has_timed_out(last_seen, BATADV_PURGE_TIMEOUT) ||
-- 
2.47.3