2023-04-11 04:17:33

by Peng Zhang

Subject: [PATCH v2 1/2] 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.

Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Peng Zhang <[email protected]>
Cc: <[email protected]>
---
lib/maple_tree.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index dd1a114d9e2b..938634bea2d6 100644
--- 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;
--
2.20.1

2023-04-11 17:44:03

by Liam R. Howlett

Subject: Re: [PATCH v2 1/2] maple_tree: Fix a potential memory leak, OOB access, or other unpredictable bug

* Peng Zhang <[email protected]> [230411 00:10]:
> 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.
>
> Fixes: 54a611b60590 ("Maple Tree: add new data structure")
> Signed-off-by: Peng Zhang <[email protected]>
> Cc: <[email protected]>

Reviewed-by: Liam R. Howlett <[email protected]>

> ---
> lib/maple_tree.c | 19 +++++++------------
> 1 file changed, 7 insertions(+), 12 deletions(-)
>
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index dd1a114d9e2b..938634bea2d6 100644
> --- 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;
> --
> 2.20.1
>