maple_tree: fix potential out-of-bounds access in mas_wr_end_piv()

Check the write offset end bounds before using it as the offset into the
pivot array.  This avoids a possible out-of-bounds access on the pivot
array if the write extends to the last slot in the node, in which case the
node maximum should be used as the end pivot.

akpm: this doesn't affect any current callers, but new users of mapletree
may encounter this problem if backported into earlier kernels, so let's
fix it in -stable kernels in case of this.

Link: https://lkml.kernel.org/r/20230506024752.2550-1-zhangpeng.00@bytedance.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 8ebc43d4cc8c58824308c7ef8362f9c1e01cfa9b..35264f1936a37cc7db31d769da0ebc69adf7a622 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -4263,11 +4263,13 @@ done:
 
 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)