From nobody Sat Oct 4 14:35:20 2025 Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5A9341459F7; Fri, 15 Aug 2025 01:49:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.56 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755222547; cv=none; b=imMBUgffzw7r3BOz5fiiZgd+ER0EDFfR0SoPlCpmZdnSJ9od7P0wAvd8714dVEvVCobfcqgAbtPtymm31W1Nlc3x3xRS2uErSAaZ86xg/Ld9lcy4K+hV23Vw7Z1hJwqcddx4U5XTbu/KSlUxoNqA5XAN2E6tFyHL3MjYHMQiMS4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755222547; c=relaxed/simple; bh=Z54yWXBe1NRvXtU74+14GPnATXdRJmNE1S2qdqNFXjg=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=IqqQb5gHljyDqqBIMgUqSjEzeUZrXA6xruaO3YjajgQmSNGiVTJibBj0+bjnWk/NnLY23+oCb9XNGo5zrAiNh+kyuw2ADtJyBxDiohHaR/RVTPfFYiz4++kgxoXNA/E8rOMGScuKAON4g/omhzwIl45bEhrzR7ZEiOBHhexGFz8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.93.142]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4c34ld3bgBzKHMtl; Fri, 15 Aug 2025 09:49:01 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.252]) by mail.maildlp.com (Postfix) with ESMTP id CB02C1A07BB; Fri, 15 Aug 2025 09:49:00 +0800 (CST) Received: from hulk-vt.huawei.com (unknown [10.67.174.121]) by APP3 (Coremail) with SMTP id _Ch0CgBHwNoCkp5oaw2bDg--.60271S2; Fri, 15 Aug 2025 09:49:00 +0800 (CST) From: Chen Ridong To: gregkh@linuxfoundation.org, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, peterz@infradead.org, zhouchengming@bytedance.com Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com Subject: [PATCH] kernfs: Fix UAF in PSI polling when open file is released Date: Fri, 15 Aug 2025 01:34:29 +0000 Message-Id: <20250815013429.1255241-1-chenridong@huaweicloud.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: _Ch0CgBHwNoCkp5oaw2bDg--.60271S2 X-Coremail-Antispam: 1UD129KBjvJXoWxGF4rKryxWw1UCr1UtF43Wrg_yoW5uFy7pa n8Ary8G395Xr1DCrs7ta409F1rCan7Xay7Wan7G39ay3W3tr1vywn29r1Yqr1kAFs3JrZF qF9I93yjkw4YyF7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUv2b4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcxkI7VAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7MxkF7I0E n4kS14v26r1q6r43MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I 0E5I8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWU tVW8ZwCIc40Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcV CY1x0267AKxVWUJVW8JwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAF wI0_Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa 7IU17KsUUUUUU== X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ Content-Type: text/plain; charset="utf-8" From: Chen Ridong A use-after-free (UAF) vulnerability was identified in the PSI (Pressure Stall Information) monitoring mechanism: BUG: KASAN: slab-use-after-free in psi_trigger_poll+0x3c/0x140 Read of size 8 at addr ffff3de3d50bd308 by task systemd/1 psi_trigger_poll+0x3c/0x140 cgroup_pressure_poll+0x70/0xa0 cgroup_file_poll+0x8c/0x100 kernfs_fop_poll+0x11c/0x1c0 ep_item_poll.isra.0+0x188/0x2c0 Allocated by task 1: cgroup_file_open+0x88/0x388 kernfs_fop_open+0x73c/0xaf0 do_dentry_open+0x5fc/0x1200 vfs_open+0xa0/0x3f0 do_open+0x7e8/0xd08 path_openat+0x2fc/0x6b0 do_filp_open+0x174/0x368 Freed by task 8462: cgroup_file_release+0x130/0x1f8 kernfs_drain_open_files+0x17c/0x440 kernfs_drain+0x2dc/0x360 kernfs_show+0x1b8/0x288 cgroup_file_show+0x150/0x268 cgroup_pressure_write+0x1dc/0x340 cgroup_file_write+0x274/0x548 Reproduction Steps: 1. Open test/cpu.pressure and establish epoll monitoring 2. Disable monitoring: echo 0 > test/cgroup.pressure 3. Re-enable monitoring: echo 1 > test/cgroup.pressure The race condition occurs because: 1. When cgroup.pressure is disabled (echo 0 > cgroup.pressure), it: - Releases PSI triggers via cgroup_file_release() - Frees of->priv through kernfs_drain_open_files() 2. While epoll still holds reference to the file and continues polling 3. Re-enabling (echo 1 > cgroup.pressure) accesses freed of->priv epolling disable/enable cgroup.pressure fd=3Dopen(cpu.pressure) while(1) ... epoll_wait kernfs_fop_poll kernfs_get_active =3D true echo 0 > cgroup.pressure ... cgroup_file_show kernfs_show // inactive kn kernfs_drain_open_files cft->release(of); kfree(ctx); ... kernfs_get_active =3D false echo 1 > cgroup.pressure kernfs_show kernfs_activate_one(kn); kernfs_fop_poll kernfs_get_active =3D true cgroup_file_poll psi_trigger_poll // UAF ... end: close(fd) Fix this by adding released flag check in kernfs_fop_poll(), which is treated as kn is inactive. Fixes: 34f26a15611a ("sched/psi: Per-cgroup PSI accounting disable/re-enabl= e interface") Reported-by: Zhang Zhantian Signed-off-by: Chen Ridong --- fs/kernfs/file.c | 2 +- kernel/cgroup/cgroup.c | 1 + 2 files changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index a6c692cac616..d5d01f0b9392 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -852,7 +852,7 @@ static __poll_t kernfs_fop_poll(struct file *filp, poll= _table *wait) struct kernfs_node *kn =3D kernfs_dentry_node(filp->f_path.dentry); __poll_t ret; =20 - if (!kernfs_get_active(kn)) + if (of->released || !kernfs_get_active(kn)) return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI; =20 if (kn->attr.ops->poll) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 312c6a8b55bb..d8b82afed181 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -4159,6 +4159,7 @@ static void cgroup_file_release(struct kernfs_open_fi= le *of) cft->release(of); put_cgroup_ns(ctx->ns); kfree(ctx); + of->priv =3D NULL; } =20 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf, --=20 2.34.1