maple_tree: fix a potential memory leak, OOB access, or other unpredictable bug

In mas_alloc_nodes(), "node->node_count = 0" means to initialize the
node_count field of the new node, but the node may not be a new node.  It
may be a node that existed before and node_count has a value, setting it
to 0 will cause a memory leak.  At this time, mas->alloc->total will be
greater than the actual number of nodes in the linked list, which may
cause many other errors.  For example, out-of-bounds access in
mas_pop_node(), and mas_pop_node() may return addresses that should not be
used.  Fix it by initializing node_count only for new nodes.

Also, by the way, an if-else statement was removed to simplify the code.

Link: https://lkml.kernel.org/r/20230411041005.26205-1-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 db60edb55f2f55377a4100f6655e750f39a12296..7ff2a821a2a123b82173667f6a4ea27ac2df32e8 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1303,26 +1303,21 @@ static inline void mas_alloc_nodes(struct ma_state *mas, gfp_t gfp)
        node = mas->alloc;
        node->request_count = 0;
        while (requested) {
-               max_req = MAPLE_ALLOC_SLOTS;
-               if (node->node_count) {
-                       unsigned int offset = node->node_count;
-
-                       slots = (void **)&node->slot[offset];
-                       max_req -= offset;
-               } else {
-                       slots = (void **)&node->slot;
-               }
-
+               max_req = MAPLE_ALLOC_SLOTS - node->node_count;
+               slots = (void **)&node->slot[node->node_count];
                max_req = min(requested, max_req);
                count = mt_alloc_bulk(gfp, max_req, slots);
                if (!count)
                        goto nomem_bulk;
 
+               if (node->node_count == 0) {
+                       node->slot[0]->node_count = 0;
+                       node->slot[0]->request_count = 0;
+               }
+
                node->node_count += count;
                allocated += count;
                node = node->slot[0];
-               node->node_count = 0;
-               node->request_count = 0;
                requested -= count;
        }
        mas->alloc->total = allocated;