From cf3b71421ca00807328c6d9cd242f9de3b77a4bf Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Thu, 23 Apr 2026 08:02:52 -0700 Subject: mm/damon/sysfs-schemes: protect path kfree() with damon_sysfs_lock 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. Link: https://lore.kernel.org/20260423150253.111520-3-sj@kernel.org Fixes: c41e253a411e ("mm/damon/sysfs-schemes: implement path file under quota goal directory") Co-developed-by: Junxi Qian Signed-off-by: Junxi Qian Signed-off-by: SeongJae Park Cc: # 6.19.x Signed-off-by: Andrew Morton --- mm/damon/sysfs-schemes.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c index 8d32a20531d4..245d63808411 100644 --- a/mm/damon/sysfs-schemes.c +++ b/mm/damon/sysfs-schemes.c @@ -1197,8 +1197,13 @@ static ssize_t path_show(struct kobject *kobj, { 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 *kobj, 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; } -- cgit v1.2.3