linux-hardening - [PATCH] rcu: Annotate struct kvfree_rcu_bulk_data with __counted

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Message-ID: <20240807095459.1400-2-thorsten.blum@toblux.com>
Date: Wed,  7 Aug 2024 11:55:00 +0200
From: Thorsten Blum <thorsten.blum@...lux.com>
To: paulmck@...nel.org,
	frederic@...nel.org,
	neeraj.upadhyay@...nel.org,
	joel@...lfernandes.org,
	josh@...htriplett.org,
	boqun.feng@...il.com,
	urezki@...il.com,
	rostedt@...dmis.org,
	mathieu.desnoyers@...icios.com,
	jiangshanlai@...il.com,
	qiang.zhang1211@...il.com,
	kees@...nel.org,
	gustavoars@...nel.org
Cc: rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Thorsten Blum <thorsten.blum@...lux.com>
Subject: [PATCH] rcu: Annotate struct kvfree_rcu_bulk_data with __counted_by()

Add the __counted_by compiler attribute to the flexible array member
records to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Increment nr_records before adding a new pointer to the records array.

Signed-off-by: Thorsten Blum <thorsten.blum@...lux.com>
---
 kernel/rcu/tree.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e641cc681901..76d8d75dd8b3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3227,7 +3227,7 @@ struct kvfree_rcu_bulk_data {
 	struct list_head list;
 	struct rcu_gp_oldstate gp_snap;
 	unsigned long nr_records;
-	void *records[];
+	void *records[] __counted_by(nr_records);
 };
 
 /*
@@ -3767,7 +3767,8 @@ add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
 	}
 
 	// Finally insert and update the GP for this page.
-	bnode->records[bnode->nr_records++] = ptr;
+	bnode->nr_records++;
+	bnode->records[bnode->nr_records - 1] = ptr;
 	get_state_synchronize_rcu_full(&bnode->gp_snap);
 	atomic_inc(&(*krcp)->bulk_count[idx]);
 
-- 
2.45.2