[PATCH] maple_tree: Fix potential out-of-bounds access in mas_wr_end_piv()

[Peng Zhang]

Access to the pivots array may be out of bounds. Fix it by changing the
code to ensure that the index of the pivots does not go out of bounds.
It is difficult to assess user-visible impact.

Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx>
---
 lib/maple_tree.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 110a36479dced..5a49327444d76 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -4263,11 +4263,13 @@ static inline bool mas_wr_slot_store(struct ma_wr_state *wr_mas)
 
 static inline void mas_wr_end_piv(struct ma_wr_state *wr_mas)
 {
-	while ((wr_mas->mas->last > wr_mas->end_piv) &&
-	       (wr_mas->offset_end < wr_mas->node_end))
-		wr_mas->end_piv = wr_mas->pivots[++wr_mas->offset_end];
+	while ((wr_mas->offset_end < wr_mas->node_end) &&
+	       (wr_mas->mas->last > wr_mas->pivots[wr_mas->offset_end]))
+		wr_mas->offset_end++;
 
-	if (wr_mas->mas->last > wr_mas->end_piv)
+	if (wr_mas->offset_end < wr_mas->node_end)
+		wr_mas->end_piv = wr_mas->pivots[wr_mas->offset_end];
+	else
 		wr_mas->end_piv = wr_mas->mas->max;
 }
 
@@ -4424,7 +4426,6 @@ static inline void *mas_wr_store_entry(struct ma_wr_state *wr_mas)
 	}
 
 	/* At this point, we are at the leaf node that needs to be altered. */
-	wr_mas->end_piv = wr_mas->r_max;
 	mas_wr_end_piv(wr_mas);
 
 	if (!wr_mas->entry)
-- 
2.20.1