2024-01-30 01:34:55

by Johannes Weiner

Subject: [PATCH] mm: zswap: fix objcg use-after-free in entry destruction

In the per-memcg LRU universe, LRU removal uses entry->objcg to
determine which list count needs to be decreased. Drop the objcg
reference after updating the LRU, to fix a possible use-after-free.

Fixes: a65b0e7607cc ("zswap: make shrinking memcg-aware")
Signed-off-by: Johannes Weiner <[email protected]>
---
mm/zswap.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index de68a5928527..7f88b3a77e4a 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -522,10 +522,6 @@ static struct zpool *zswap_find_zpool(struct zswap_entry *entry)
*/
static void zswap_free_entry(struct zswap_entry *entry)
{
- if (entry->objcg) {
- obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
- obj_cgroup_put(entry->objcg);
- }
if (!entry->length)
atomic_dec(&zswap_same_filled_pages);
else {
@@ -534,6 +530,10 @@ static void zswap_free_entry(struct zswap_entry *entry)
atomic_dec(&entry->pool->nr_stored);
zswap_pool_put(entry->pool);
}
+ if (entry->objcg) {
+ obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
+ obj_cgroup_put(entry->objcg);
+ }
zswap_entry_cache_free(entry);
atomic_dec(&zswap_stored_pages);
zswap_update_total_size();
--
2.43.0

2024-01-30 01:48:14

by Yosry Ahmed

Subject: Re: [PATCH] mm: zswap: fix objcg use-after-free in entry destruction

On Mon, Jan 29, 2024 at 08:34:38PM -0500, Johannes Weiner wrote:
> In the per-memcg LRU universe, LRU removal uses entry->objcg to
> determine which list count needs to be decreased. Drop the objcg
> reference after updating the LRU, to fix a possible use-after-free.
>
> Fixes: a65b0e7607cc ("zswap: make shrinking memcg-aware")

Lots of hotfixes for zswap in v6.8 these couple of days :)

> Signed-off-by: Johannes Weiner <[email protected]>

Acked-by: Yosry Ahmed <[email protected]>

Thanks!

2024-01-30 02:41:44

by Chengming Zhou

Subject: Re: [PATCH] mm: zswap: fix objcg use-after-free in entry destruction

On 2024/1/30 09:34, Johannes Weiner wrote:
> In the per-memcg LRU universe, LRU removal uses entry->objcg to
> determine which list count needs to be decreased. Drop the objcg
> reference after updating the LRU, to fix a possible use-after-free.
>
> Fixes: a65b0e7607cc ("zswap: make shrinking memcg-aware")
> Signed-off-by: Johannes Weiner <[email protected]>

LGTM, thanks!

Reviewed-by: Chengming Zhou <[email protected]>

> ---
> mm/zswap.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index de68a5928527..7f88b3a77e4a 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -522,10 +522,6 @@ static struct zpool *zswap_find_zpool(struct zswap_entry *entry)
> */
> static void zswap_free_entry(struct zswap_entry *entry)
> {
> - if (entry->objcg) {
> - obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
> - obj_cgroup_put(entry->objcg);
> - }
> if (!entry->length)
> atomic_dec(&zswap_same_filled_pages);
> else {
> @@ -534,6 +530,10 @@ static void zswap_free_entry(struct zswap_entry *entry)
> atomic_dec(&entry->pool->nr_stored);
> zswap_pool_put(entry->pool);
> }
> + if (entry->objcg) {
> + obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
> + obj_cgroup_put(entry->objcg);
> + }
> zswap_entry_cache_free(entry);
> atomic_dec(&zswap_stored_pages);
> zswap_update_total_size();

2024-01-30 07:27:00

by Nhat Pham

Subject: Re: [PATCH] mm: zswap: fix objcg use-after-free in entry destruction

On Mon, Jan 29, 2024 at 5:34 PM Johannes Weiner <[email protected]> wrote:
>
> In the per-memcg LRU universe, LRU removal uses entry->objcg to
> determine which list count needs to be decreased. Drop the objcg
> reference after updating the LRU, to fix a possible use-after-free.
>
> Fixes: a65b0e7607cc ("zswap: make shrinking memcg-aware")
> Signed-off-by: Johannes Weiner <[email protected]>
> ---
> mm/zswap.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index de68a5928527..7f88b3a77e4a 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -522,10 +522,6 @@ static struct zpool *zswap_find_zpool(struct zswap_entry *entry)
> */
> static void zswap_free_entry(struct zswap_entry *entry)
> {
> - if (entry->objcg) {
> - obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
> - obj_cgroup_put(entry->objcg);
> - }
> if (!entry->length)
> atomic_dec(&zswap_same_filled_pages);
> else {
> @@ -534,6 +530,10 @@ static void zswap_free_entry(struct zswap_entry *entry)
> atomic_dec(&entry->pool->nr_stored);
> zswap_pool_put(entry->pool);
> }
> + if (entry->objcg) {
> + obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
> + obj_cgroup_put(entry->objcg);
> + }

Nice catch!
Reviewed-by: Nhat Pham <[email protected]>

> zswap_entry_cache_free(entry);
> atomic_dec(&zswap_stored_pages);
> zswap_update_total_size();
> --
> 2.43.0
>