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b=udodKoFyHuHw4e0+rQfbvCgxWvRXAMA4MMsmXi6USJIVqOK57GtkP7btDpyX7gqOF qUGCCUA0oc8cegm1UYvT70jB1q53LkMvmvljziC78Fe9KXro2TZBkDcICXg90kFLHG 0wAz4HROL6k7Icrw4KMmPOZK+AZsHcUxNh6saUH29fCbEoKaMSju4n9OxbjMWNJqA7 rxgfKOL8sUqN+j7SpEkM3FZBtv8c53toiG++jNgiZUCGKeeK3HFxTZ+q9Yi1KkfqUS FLgTNGmPFezzVwz/yclBqy6GAseYw/iokdRYXDYzLmhYWrXqXPMjGtGlFX+d0v7NRM qoFYWjLSd4v2g== From: SeongJae Park To: Cc: SeongJae Park , "# 6 . 2 . x" , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH] mm/damon/sysfs-schemes: delete tried region in regions_rmdirs() Date: Sat, 16 May 2026 14:14:35 -0700 Message-ID: <20260516211436.1883-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: pjx3s86hcr6kupp8yydmmi397k1gx188 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: C643914000A X-Rspam-User: X-HE-Tag: 1778966082-699204 X-HE-Meta: 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 Vi1ni5k6 5OFmc+4GfQMvqe13WKODdtdVNh6BYmycIxReZC8TMqLPsnwzKmNzrBXcbHX96WPyJHcDIayoGvoLEGGduV3fECNxeaqqpnkdRszsmKAyQjFSA4NFpzuSd8cp9wyGNttY0XKu7GbLqehEm+4rLgQ1m8SbQFrlpH2hTBJS2z3awe+QgHzxMeoSlBMfYbDHNB2RwawQqe3i3C7PbmKMBWNIohx2nvyd9D6n7pS2R9naoJQ9/X2hFsnjx0GiuVQmhWEtTTx+VDKjouSkBMH7N53o1z0lCDrNksCxxlsW0GM68WorWuVk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: DAMON sysfs maintains the DAMOS tried region directory objects via a linked list. When the user requests refresh of the directories, DAMON sysfs removes all the region directories first, and then generate updated regions directory on the empty space. The removal function (damon_sysfs_scheme_regions_rm_dirs()) only puts the kobj objects. Deletion of the container region object from the linked list is done inside the kobj release callback function. If somehow the callback invocation is delayed, the list will contain regions list that gonna be freed. If the updated region directories creation is started in this situation, the list can be corrupted and use-after-free can happen. Because the kobj objects are managed by only DAMON sysfs, the issue cannot happen in normal situation. But, such delays can be made on kernels that built with CONFIG_DEBUG_KOBJECT_RELEASE. On the kernel, the issue can indeed be reproduced like below. # damo start --damos_action stat # cd /sys/kernel/mm/damon/admin/kdamonds/0/ # for i in {1..10}; do echo update_schemes_tried_regions > state; done # dmesg | grep underflow [ 89.296152] refcount_t: underflow; use-after-free. Fix the issue by removing the region object from the list when decrementing the reference count. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260513011920.119183-1-sj@kernel.org Fixes: 9277d0367ba1 ("mm/damon/sysfs-schemes: implement scheme region directory") Cc: # 6.2.x Signed-off-by: SeongJae Park --- mm/damon/sysfs-schemes.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c index 5d966ac864193..52627ce3a1a62 100644 --- a/mm/damon/sysfs-schemes.c +++ b/mm/damon/sysfs-schemes.c @@ -88,7 +88,6 @@ static void damon_sysfs_scheme_region_release(struct kobject *kobj) struct damon_sysfs_scheme_region *region = container_of(kobj, struct damon_sysfs_scheme_region, kobj); - list_del(®ion->list); kfree(region); } @@ -164,7 +163,7 @@ static void damon_sysfs_scheme_regions_rm_dirs( struct damon_sysfs_scheme_region *r, *next; list_for_each_entry_safe(r, next, ®ions->regions_list, list) { - /* release function deletes it from the list */ + list_del(&r->list); kobject_put(&r->kobj); regions->nr_regions--; } base-commit: 950de73f0f8bb17fc322e8f9ec09a5fbb4a72ed8 -- 2.47.3