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b=JrEjuLmYIS4mWBTUTBGJoJulPraOsKubWUrjeWM0ZikmkxlnLi2QvPIPWUTDmKaVG QTbw2+fu2ftq/9h9E/7L7eTRjXoAVTBtdg6/gf8bdItCHn9ogg+Zk5uiRJNur3ECSk MvCQscxdSQ5Ys/L01MVNp/HN5W56pmwkUStjCtw5j0/GKN8lhpBjba5j5av5F7MPjt EN8zDME6LGyRrdzKuNwRUobqU26TBNJ8g3HTDSw8HWts8D+MDMcw61OYij42u47WZV zLj8TdQxbzOhpWnQjwr+jCInYnA6iZBiDgkzPZPIPjanOQOFvYjdLeiW0y0rTgAkIW RD4hIftBJsYow== From: SeongJae Park To: Andrew Morton Cc: SeongJae Park , "# 6 . 16 . x" , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Junxi Qian Subject: [PATCH 1/2] mm/damon/sysfs-schemes: protect memcg_path kfree() with damon_sysfs_lock Date: Thu, 23 Apr 2026 08:02:51 -0700 Message-ID: <20260423150253.111520-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260423150253.111520-1-sj@kernel.org> References: <20260423150253.111520-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 5p9f1aszf7an441mra4bedz6e8791ezx X-Rspamd-Queue-Id: C852680006 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1776956583-673511 X-HE-Meta: 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 ds3zGMx9 Fi0vSbXknDNNRsc+zZ3iL92fPyEFoFqvauH4ZAvlIQ1lKz7bRhxbbxOcrNJVLjY2oERVZghT18r5VXyZN2ny1TiYuHk37ouK5YT7Re8hCbTg0vBDt9qSV933SdewVYYsb3y9GiWslKdoIe++KcDHsA+Cwkb8lPp633v4rRlfreA8+YDkGKPZdAB1+ZzEyE2zPufCgSGLIy/5HvC1DYJUSUA0DtCep+WD34/fj7ghdeg35Atdri4nnjong/Ji+x9wTRJjDeMFpqTFrr59UCUnEZPxhASlK0SdTcYTtqfmQwkBjroI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Fixes: 4f489fe6afb3 ("mm/damon/sysfs-schemes: free old damon_sysfs_scheme_filter->memcg_path on write") Cc: # 6.16.x Co-developed-by: Junxi Qian Signed-off-by: Junxi Qian Signed-off-by: SeongJae Park --- 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 5186966dafb35..8d32a20531d49 100644 --- a/mm/damon/sysfs-schemes.c +++ b/mm/damon/sysfs-schemes.c @@ -533,9 +533,14 @@ 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, @@ -550,8 +555,13 @@ 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; } -- 2.47.3