mm-damon-sysfs-schemes-protect-path-kfree-with-damon_sysfs_lock.patch removed from -mm tree

The quilt patch titled
Subject: mm/damon/sysfs-schemes: protect path kfree() with damon_sysfs_lock
has been removed from the -mm tree. Its filename was
mm-damon-sysfs-schemes-protect-path-kfree-with-damon_sysfs_lock.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: SeongJae Park <[email protected]>
Subject: mm/damon/sysfs-schemes: protect path kfree() with damon_sysfs_lock
Date: Thu, 23 Apr 2026 08:02:52 -0700

damon_sysfs_quot_goal->path can be read and written by users, via DAMON sysfs 'path' file. It can also be indirectly read, for the parameters {on,off}line committing to DAMON. The reads for parameters committing are protected by damon_sysfs_lock to avoid the sysfs files being destroyed while any of the parameters are being read. But the user-driven direct reads and writes are not protected by any lock, while the write is deallocating the path-pointing buffer. As a result, the readers could read the already freed buffer (user-after-free). Note that the user-reads don't race when the same open file is used by the writer, due to kernfs's open file locking. Nonetheless, doing the reads and writes with separate open files would be common. Fix it by protecting both the user-direct reads and writes with damon_sysfs_lock.

---

 mm/damon/sysfs-schemes.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

@@ -1197,8 +1197,13 @@ static ssize_t path_show(struct kobject
 {
 	struct damos_sysfs_quota_goal *goal = container_of(kobj,
 			struct damos_sysfs_quota_goal, kobj);
+	int len;
 
-	return sysfs_emit(buf, "%s\n", goal->path ? goal->path : "");
+	if (!mutex_trylock(&damon_sysfs_lock))
+		return -EBUSY;
+	len = sysfs_emit(buf, "%s\n", goal->path ? goal->path : "");
+	mutex_unlock(&damon_sysfs_lock);
+	return len;
 }
 
 static ssize_t path_store(struct kobject *kobj,

@@ -1213,8 +1218,13 @@ static ssize_t path_store(struct kobject
 		return -ENOMEM;
 
 	strscpy(path, buf, count + 1);
+	if (!mutex_trylock(&damon_sysfs_lock)) {
+		kfree(path);
+		return -EBUSY;
+	}
 	kfree(goal->path);
 	goal->path = path;
+	mutex_unlock(&damon_sysfs_lock);
 	return count;
 }
 

_

Patches currently in -mm which might be from [email protected] are

mm-damon-sysfs-schemes-call-missing-mem_cgroup_iter_break.patch mm-damon-fix-damos_stat-tracepoint-format-for-sz_applied.patch docs-mm-damon-maintainer-profile-add-ai-review-usage-guideline.patch