linux-kernel - [PATCH] locking/lockdep: Fix string truncation and length accounting in seq

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Message-ID: <aUVrKwedNdTYpi4d@bou-desktop>
Date: Fri, 19 Dec 2025 16:11:39 +0100
From: Boudewijn van der Heide <boudewijn@...ta-utec.com>
To: peterz@...radead.org
Cc: mingo@...hat.com, will@...nel.org, boqun.feng@...il.com,
	longman@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH] locking/lockdep: Fix string truncation and length accounting
 in seq_stats()

GCC 14 reports a -Wformat-truncation warning when appending "#%d" and
"/%d" to the lock class name in seq_stats(), as the buffer size was
insufficient and the resulting length was tracked incorrectly.

Use scnprintf() with remaining-buffer accounting to safely append the
suffixes and update namelen based on the actual number of characters
written.

Signed-off-by: Boudewijn van der Heide <boudewijn@...ta-utec.com>
---
 kernel/locking/lockdep_proc.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 1916db9aa46b..8fe977c32a3d 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -496,12 +496,14 @@ static void seq_stats(struct seq_file *m, struct lock_stat_data *data)
 
 	namelen = strlen(name);
 	if (class->name_version > 1) {
-		snprintf(name+namelen, 3, "#%d", class->name_version);
-		namelen += 2;
+		namelen += scnprintf(name + namelen,
+				sizeof(name) - namelen, "#%d",
+				class->name_version);
 	}
 	if (class->subclass) {
-		snprintf(name+namelen, 3, "/%d", class->subclass);
-		namelen += 2;
+		namelen += scnprintf(name + namelen,
+				sizeof(name) - namelen, "/%d",
+				class->subclass);
 	}
 
 	if (stats->write_holdtime.nr) {
-- 
2.47.3