[PATCH] mm/damon/sysfs-schemes: fix tried_regions setup failure cleanup

[PATCH] mm/damon/sysfs-schemes: fix tried_regions setup failure cleanup

[Guangshuo Li]

damon_sysfs_scheme_add_dirs() sets up the tried_regions directory after
the stats directory has already been created.

If damon_sysfs_scheme_set_tried_regions() fails, scheme->tried_regions
has not been assigned. The error path nevertheless jumps to
put_tried_regions_out and dereferences scheme->tried_regions while
trying to put its kobject.

This can dereference uninitialized memory because struct
damon_sysfs_scheme is allocated with kmalloc-style allocation and
scheme->tried_regions is only assigned after tried_regions setup
succeeds.

On tried_regions setup failure, start cleanup from the last successfully
created directory, stats, instead of trying to put tried_regions.

Fixes: 5181b75f438d ("mm/damon/sysfs-schemes: implement schemes/tried_regions directory")
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
---
 mm/damon/sysfs-schemes.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 329cfd0bbe9f..0668a0e53971 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2516,12 +2516,12 @@ static int damon_sysfs_scheme_add_dirs(struct damon_sysfs_scheme *scheme)
 		goto put_filters_watermarks_quotas_access_pattern_out;
 	err = damon_sysfs_scheme_set_tried_regions(scheme);
 	if (err)
-		goto put_tried_regions_out;
+		goto put_stats_out;
 	return 0;
 
-put_tried_regions_out:
-	kobject_put(&scheme->tried_regions->kobj);
-	scheme->tried_regions = NULL;
+put_stats_out:
+	kobject_put(&scheme->stats->kobj);
+	scheme->stats = NULL;
 put_filters_watermarks_quotas_access_pattern_out:
 	kobject_put(&scheme->ops_filters->kobj);
 	scheme->ops_filters = NULL;
-- 
2.43.0

Re: [PATCH] mm/damon/sysfs-schemes: fix tried_regions setup failure cleanup

[SJ Park]

Hello Guangshuo,

On Wed,  8 Jul 2026 16:01:07 +0800 Guangshuo Li <lgs201920130244@gmail.com> wrote:

> damon_sysfs_scheme_add_dirs() sets up the tried_regions directory after
> the stats directory has already been created.
> 
> If damon_sysfs_scheme_set_tried_regions() fails, scheme->tried_regions
> has not been assigned. The error path nevertheless jumps to
> put_tried_regions_out and dereferences scheme->tried_regions while
> trying to put its kobject.
> 
> This can dereference uninitialized memory because struct
> damon_sysfs_scheme is allocated with kmalloc-style allocation and
> scheme->tried_regions is only assigned after tried_regions setup
> succeeds.
> 
> On tried_regions setup failure, start cleanup from the last successfully
> created directory, stats, instead of trying to put tried_regions.

Thank you for this patch!  However, it seems a same fix is already merged into
the mainline as commit 05ea83ee88ca ("mm/damon/sysfs-schemes: put stats for
scheme_add_dirs() internal error").

So, unfortunately we will not be able to merge this patch.


Thanks,
SJ

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