netdev - [PATCH net 3/3] net: dsa: sja1105: fix kasan out-of-bounds warning in sja1105_table_delete

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Message-Id: <20250318115716.2124395-4-vladimir.oltean@nxp.com>
Date: Tue, 18 Mar 2025 13:57:16 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: netdev@...r.kernel.org
Cc: Andrew Lunn <andrew@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Florian Fainelli <f.fainelli@...il.com>
Subject: [PATCH net 3/3] net: dsa: sja1105: fix kasan out-of-bounds warning in sja1105_table_delete_entry()

There are actually 2 problems:
- deleting the last element doesn't require the memmove of elements
  [i + 1, end) over it. Actually, element i+1 is out of bounds.
- The memmove itself should move size - i - 1 elements, because the last
  element is out of bounds.

The out-of-bounds element still remains out of bounds after being
accessed, so the problem is only that we touch it, not that it becomes
in active use. But I suppose it can lead to issues if the out-of-bounds
element is part of an unmapped page.

Fixes: 6666cebc5e30 ("net: dsa: sja1105: Add support for VLAN operations")
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/dsa/sja1105/sja1105_static_config.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/sja1105/sja1105_static_config.c b/drivers/net/dsa/sja1105/sja1105_static_config.c
index 3d790f8c6f4d..ffece8a400a6 100644
--- a/drivers/net/dsa/sja1105/sja1105_static_config.c
+++ b/drivers/net/dsa/sja1105/sja1105_static_config.c
@@ -1917,8 +1917,10 @@ int sja1105_table_delete_entry(struct sja1105_table *table, int i)
 	if (i > table->entry_count)
 		return -ERANGE;
 
-	memmove(entries + i * entry_size, entries + (i + 1) * entry_size,
-		(table->entry_count - i) * entry_size);
+	if (i + 1 < table->entry_count) {
+		memmove(entries + i * entry_size, entries + (i + 1) * entry_size,
+			(table->entry_count - i - 1) * entry_size);
+	}
 
 	table->entry_count--;
 
-- 
2.34.1