[PATCH 4.14 126/186] dm btree: add a defensive bounds check to insert_at()

[Greg Kroah-Hartman]

From: Joe Thornber <ejt@xxxxxxxxxx>

[ Upstream commit 85bca3c05b6cca31625437eedf2060e846c4bbad ]

Corrupt metadata could trigger an out of bounds write.

Signed-off-by: Joe Thornber <ejt@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/md/persistent-data/dm-btree.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/md/persistent-data/dm-btree.c b/drivers/md/persistent-data/dm-btree.c
index 8aae0624a2971..6383afb88f319 100644
--- a/drivers/md/persistent-data/dm-btree.c
+++ b/drivers/md/persistent-data/dm-btree.c
@@ -83,14 +83,16 @@ void inc_children(struct dm_transaction_manager *tm, struct btree_node *n,
 }
 
 static int insert_at(size_t value_size, struct btree_node *node, unsigned index,
-		      uint64_t key, void *value)
-		      __dm_written_to_disk(value)
+		     uint64_t key, void *value)
+	__dm_written_to_disk(value)
 {
 	uint32_t nr_entries = le32_to_cpu(node->header.nr_entries);
+	uint32_t max_entries = le32_to_cpu(node->header.max_entries);
 	__le64 key_le = cpu_to_le64(key);
 
 	if (index > nr_entries ||
-	    index >= le32_to_cpu(node->header.max_entries)) {
+	    index >= max_entries ||
+	    nr_entries >= max_entries) {
 		DMERR("too many entries in btree node for insert");
 		__dm_unbless_for_disk(value);
 		return -ENOMEM;
-- 
2.34.1