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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 4c7yTM1PdrzKHLxZ; Sat, 23 Aug 2025 08:23:35 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.252]) by mail.maildlp.com (Postfix) with ESMTP id B10CE1A0359; Sat, 23 Aug 2025 08:23:34 +0800 (CST) Received: from [10.67.109.79] (unknown [10.67.109.79]) by APP3 (Coremail) with SMTP id _Ch0CgBHwNoGCqloNYgUEg--.7432S2; Sat, 23 Aug 2025 08:23:34 +0800 (CST) Message-ID: <1cf4c031-fb21-4986-9356-92f69697d491@huaweicloud.com> Date: Sat, 23 Aug 2025 08:23:34 +0800 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] kernfs: Fix UAF in polling when open file is released To: Tejun Heo Cc: gregkh@linuxfoundation.org, hannes@cmpxchg.org, mkoutny@suse.com, peterz@infradead.org, zhouchengming@bytedance.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com, libaokun1@huawei.com References: <20250822070715.1565236-1-chenridong@huaweicloud.com> <20250822070715.1565236-2-chenridong@huaweicloud.com> Content-Language: en-US From: Chen Ridong In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CM-TRANSID:_Ch0CgBHwNoGCqloNYgUEg--.7432S2 X-Coremail-Antispam: 1UD129KBjvJXoWxWr48tFy3CFy8tFW3tF1DZFb_yoW5WFWDpa 98CF15K3ykXryUAw4IqF1093W8tayxJFWxtFn7Kr9ava43Kryvy3WI9r15XFykArsxJr47 t3ZIk34jyw45AaUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvjb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Ar0_tr1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Cr0_Gr1UM28EF7xvwVC2z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I 0E14v26rxl6s0DM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40E x7xfMcIj6xIIjxv20xvE14v26r106r15McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x 0Yz7v_Jr0_Gr1lF7xvr2IY64vIr41lFIxGxcIEc7CjxVA2Y2ka0xkIwI1lc7CjxVAaw2AF wI0_Jw0_GFyl42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4 xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43 MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I 0E14v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWU JVW8JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxUOB MKDUUUU X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ On 2025/8/23 1:46, Tejun Heo wrote: > On Fri, Aug 22, 2025 at 07:07:14AM +0000, Chen Ridong wrote: >> 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=open(cpu.pressure) >> while(1) >> ... >> epoll_wait >> kernfs_fop_poll >> kernfs_get_active = true echo 0 > cgroup.pressure >> ... cgroup_file_show >> kernfs_show >> // inactive kn >> kernfs_drain_open_files >> cft->release(of); >> kfree(ctx); >> ... >> kernfs_get_active = false >> echo 1 > cgroup.pressure >> kernfs_show >> kernfs_activate_one(kn); >> kernfs_fop_poll >> kernfs_get_active = true >> cgroup_file_poll >> psi_trigger_poll >> // UAF >> ... >> end: close(fd) >> >> To address this issue, introduce kernfs_get_active_of() for kernfs open >> files to obtain active references. This function will fail if the open file >> has been released. Replace kernfs_get_active() with kernfs_get_active_of() >> to prevent further operations on released file descriptors. >> >> Fixes: 34f26a15611a ("sched/psi: Per-cgroup PSI accounting disable/re-enable interface") >> Reported-by: Zhang Zhaotian >> Signed-off-by: Chen Ridong > > Acked-by: Tejun Heo > > Thanks. > Thanks -- Best regards, Ridong