The commit 2c653d0ee2ae ("ksm: introduce ksm_max_page_sharing per page
deduplication limit") introduced a possible failure case in the
stable_tree_insert(), where we may free the new allocated stable_node_dup
if we fail to prepare the missing chain node.
Then that kfolio return and unlock with a freed stable_node set... And
any MM activities can come in to access kfolio->mapping, so UAF.
Fix it by moving folio_set_stable_node() to the end after stable_node
is inserted successfully.
Fixes: 2c653d0ee2ae ("ksm: introduce ksm_max_page_sharing per page deduplication limit")
Signed-off-by: Chengming Zhou <[email protected]>
---
mm/ksm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/ksm.c b/mm/ksm.c
index e1034bf1c937..a8b76af5cf64 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2153,7 +2153,6 @@ static struct ksm_stable_node *stable_tree_insert(struct folio *kfolio)
INIT_HLIST_HEAD(&stable_node_dup->hlist);
stable_node_dup->kpfn = kpfn;
- folio_set_stable_node(kfolio, stable_node_dup);
stable_node_dup->rmap_hlist_len = 0;
DO_NUMA(stable_node_dup->nid = nid);
if (!need_chain) {
@@ -2172,6 +2171,8 @@ static struct ksm_stable_node *stable_tree_insert(struct folio *kfolio)
stable_node_chain_add_dup(stable_node_dup, stable_node);
}
+ folio_set_stable_node(kfolio, stable_node_dup);
+
return stable_node_dup;
}
---
base-commit: 7e8aafe0636cdcc5c9699ced05ff1f8ffcb937e2
change-id: 20240513-b4-ksm-stable-node-uaf-ccc7fe2fd6bd
Best regards,
--
Chengming Zhou <[email protected]>
On 13.05.24 05:07, Chengming Zhou wrote:
> The commit 2c653d0ee2ae ("ksm: introduce ksm_max_page_sharing per page
> deduplication limit") introduced a possible failure case in the
> stable_tree_insert(), where we may free the new allocated stable_node_dup
> if we fail to prepare the missing chain node.
>
> Then that kfolio return and unlock with a freed stable_node set... And
> any MM activities can come in to access kfolio->mapping, so UAF.
>
> Fix it by moving folio_set_stable_node() to the end after stable_node
> is inserted successfully.
>
> Fixes: 2c653d0ee2ae ("ksm: introduce ksm_max_page_sharing per page deduplication limit")
> Signed-off-by: Chengming Zhou <[email protected]>
> ---
> mm/ksm.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index e1034bf1c937..a8b76af5cf64 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -2153,7 +2153,6 @@ static struct ksm_stable_node *stable_tree_insert(struct folio *kfolio)
>
> INIT_HLIST_HEAD(&stable_node_dup->hlist);
> stable_node_dup->kpfn = kpfn;
> - folio_set_stable_node(kfolio, stable_node_dup);
> stable_node_dup->rmap_hlist_len = 0;
> DO_NUMA(stable_node_dup->nid = nid);
> if (!need_chain) {
> @@ -2172,6 +2171,8 @@ static struct ksm_stable_node *stable_tree_insert(struct folio *kfolio)
> stable_node_chain_add_dup(stable_node_dup, stable_node);
> }
>
> + folio_set_stable_node(kfolio, stable_node_dup);
> +
> return stable_node_dup;
Looks correct to me.
We might now link the node before the folio->mapping is set up. Do we
care? Don't think so.
Acked-by: David Hildenbrand <[email protected]>
--
Cheers,
David / dhildenb
On 2024/5/15 04:46, David Hildenbrand wrote:
> On 13.05.24 05:07, Chengming Zhou wrote:
>> The commit 2c653d0ee2ae ("ksm: introduce ksm_max_page_sharing per page
>> deduplication limit") introduced a possible failure case in the
>> stable_tree_insert(), where we may free the new allocated stable_node_dup
>> if we fail to prepare the missing chain node.
>>
>> Then that kfolio return and unlock with a freed stable_node set... And
>> any MM activities can come in to access kfolio->mapping, so UAF.
>>
>> Fix it by moving folio_set_stable_node() to the end after stable_node
>> is inserted successfully.
>>
>> Fixes: 2c653d0ee2ae ("ksm: introduce ksm_max_page_sharing per page deduplication limit")
>> Signed-off-by: Chengming Zhou <[email protected]>
>> ---
>> mm/ksm.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/ksm.c b/mm/ksm.c
>> index e1034bf1c937..a8b76af5cf64 100644
>> --- a/mm/ksm.c
>> +++ b/mm/ksm.c
>> @@ -2153,7 +2153,6 @@ static struct ksm_stable_node *stable_tree_insert(struct folio *kfolio)
>> INIT_HLIST_HEAD(&stable_node_dup->hlist);
>> stable_node_dup->kpfn = kpfn;
>> - folio_set_stable_node(kfolio, stable_node_dup);
>> stable_node_dup->rmap_hlist_len = 0;
>> DO_NUMA(stable_node_dup->nid = nid);
>> if (!need_chain) {
>> @@ -2172,6 +2171,8 @@ static struct ksm_stable_node *stable_tree_insert(struct folio *kfolio)
>> stable_node_chain_add_dup(stable_node_dup, stable_node);
>> }
>> + folio_set_stable_node(kfolio, stable_node_dup);
>> +
>> return stable_node_dup;
>
> Looks correct to me.
>
> We might now link the node before the folio->mapping is set up. Do we care? Don't think so.
Yeah, it shouldn't be a problem, although it doesn't look very nice.
Another way to fix maybe "folio_set_stable_node(folio, NULL)" in the failure case,
which is safe since we have held the folio lock.
>
> Acked-by: David Hildenbrand <[email protected]>
>
Thanks.