Re: [PATCH 2/2] maple_tree: Fix a potential memory leak, OOB access, or other unpredictable bug
From: Peng Zhang
Date: Mon Apr 10 2023 - 09:28:23 EST
在 2023/4/10 21:12, Liam R. Howlett 写道:
* Peng Zhang <perlyzhang@xxxxxxxxx> [230410 08:58]:
在 2023/4/10 20:43, Liam R. Howlett 写道:
* Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> [230407 00:10]:
In mas_alloc_nodes(), there is such a piece of code:
while (requested) {
...
node->node_count = 0;
...
}
You don't need to quote code in your commit message since it is
available in the change log or in the file itself.
Ok, I will change it in the next version.
"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.
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
lib/maple_tree.c | 16 ++++------------
1 file changed, 4 insertions(+), 12 deletions(-)
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 65fd861b30e1..9e25b3215803 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1249,26 +1249,18 @@ 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];
Thanks, this is much cleaner.
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->node_count += count;
allocated += count;
node = node->slot[0];
- node->node_count = 0;
- node->request_count = 0;
Why are we not clearing request_count anymore?
Because the node pointed to by the variable "node"
must not be the head node of the linked list at
this time, we only need to maintain the information
of the head node.
Right, at this time it is not the head node, but could it become the
head node with invalid data? I think it can, because we don't
explicitly set it in mas_pop_node()?
1. Actually in mas_pop_node(), when a node becomes the head node,
we initialize its total field and request_count field.
2. The total field and request_count field of any non-head node,
even if we initialize it, cannot be considered a valid value.
Imagine if the request_count of the head node is changed, then
we don't actually change the request_count of the non-head nodes,
so it is an invalid value anyway.
In any case, be sure to mention that you make a change like this in the
change log, like "Drop setting the resquest_count as it is unnecessary
because.." in a new paragraph, so that it is not missed.
I thought it was a small change that wasn't written in the changelog.
In the next version and any future patches, I will write down the
details of any changes.
Thanks.
requested -= count;
}
mas->alloc->total = allocated;
--
2.20.1