From: SeongJae Park <sj@kernel.org> stable inclusion from stable-v6.12.88 commit c88802d0e8edd14b6cd2daf3000f99adbc4c85c5 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15373 CVE: CVE-2026-46121 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit 1e68eb96e8beb1abefd12dd22c5637795d8a877e upstream. Patch series "mm/damon/sysfs-schemes: fix use-after-free for [memcg_]path". Reads of 'memcg_path' and 'path' files in DAMON sysfs interface could race with their writes, results in use-after-free. Fix those. This patch (of 2): damon_sysfs_scheme_filter->mmecg_path can be read and written by users, via DAMON sysfs memcg_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 memcg_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/20260423150253.111520-1-sj@kernel.org Link: https://lore.kernel.org/20260423150253.111520-2-sj@kernel.org Fixes: 4f489fe6afb3 ("mm/damon/sysfs-schemes: free old damon_sysfs_scheme_filter->memcg_path on write") Co-developed-by: Junxi Qian <qjx1298677004@gmail.com> Signed-off-by: Junxi Qian <qjx1298677004@gmail.com> Signed-off-by: SeongJae Park <sj@kernel.org> Cc: <stable@vger.kernel.org> # 6.16.x Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Wupeng Ma <mawupeng1@huawei.com> --- 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 13229cf9c7d1f..1c1662db8f80f 100644 --- a/mm/damon/sysfs-schemes.c +++ b/mm/damon/sysfs-schemes.c @@ -360,9 +360,14 @@ static ssize_t memcg_path_show(struct kobject *kobj, { struct damon_sysfs_scheme_filter *filter = container_of(kobj, struct damon_sysfs_scheme_filter, kobj); + int len; - return sysfs_emit(buf, "%s\n", + if (!mutex_trylock(&damon_sysfs_lock)) + return -EBUSY; + len = sysfs_emit(buf, "%s\n", filter->memcg_path ? filter->memcg_path : ""); + mutex_unlock(&damon_sysfs_lock); + return len; } static ssize_t memcg_path_store(struct kobject *kobj, @@ -376,8 +381,13 @@ static ssize_t memcg_path_store(struct kobject *kobj, return -ENOMEM; strscpy(path, buf, count + 1); + if (!mutex_trylock(&damon_sysfs_lock)) { + kfree(path); + return -EBUSY; + } kfree(filter->memcg_path); filter->memcg_path = path; + mutex_unlock(&damon_sysfs_lock); return count; } -- 2.43.0