From nobody Wed Feb 11 00:59:29 2026 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 A2FE617C77; Thu, 8 Jan 2026 01:53:04 +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=1767837188; cv=none; b=tlr8cLRoYEiCBueRMESM+fvxndlkTYAxGC/RB1/FwIig1vU7rB8RmRFruKSjNZHi9bgSQfHTtYSzMraYlrVxTnfCYvz+EhguXqgKze1ZLkGFdt7XGC9b80hAMMZoLS94NOJpi3e0BoYUtj750tXfql4Fym18f0iqgbwZJtHb5fs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767837188; c=relaxed/simple; bh=XgZrthFT1lbb9PsLOPRpfTbT5iylEyW16lqf0VbVdpw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=RxjVkxzdx0O4aKlLLYo1WDLK+yzx0UgJmbY8ka9tsZlHdG3jqANyfhIAKg7Z4p4q52Jt7lTpIq2ZZ/DLda/CVQqZ/Zg6SMjDBDIzW/3RKE/oOT18B6gKhd2RQqGl1XRv3PYS13/KZdeaU1wdiDsZZxYntPKdonHVPDipJoLkEQg= 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 [172.19.163.170]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4dmnw41WF9zKHMTj; Thu, 8 Jan 2026 09:52:20 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 54EEE4056F; Thu, 8 Jan 2026 09:53:02 +0800 (CST) Received: from huaweicloud.com (unknown [10.50.87.129]) by APP4 (Coremail) with SMTP id gCh0CgAXd_f8DV9pVBQTDA--.41552S6; Thu, 08 Jan 2026 09:53:02 +0800 (CST) From: Zheng Qixing To: tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk, yukuai@fnnas.com Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, yangerkun@huawei.com, houtao1@huawei.com, zhengqixing@huawei.com Subject: [PATCH 2/3] blk-cgroup: fix uaf in blkcg_activate_policy() racing with blkg_free_workfn() Date: Thu, 8 Jan 2026 09:44:15 +0800 Message-Id: <20260108014416.3656493-3-zhengqixing@huaweicloud.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20260108014416.3656493-1-zhengqixing@huaweicloud.com> References: <20260108014416.3656493-1-zhengqixing@huaweicloud.com> 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: gCh0CgAXd_f8DV9pVBQTDA--.41552S6 X-Coremail-Antispam: 1UD129KBjvJXoWxXFyrJr4kuFW7GF4UJw15CFg_yoW5uF45pr Z8KryxA340gryUAFsF9w12q348ta9Yqry5JrWxGr43uFsxuw1F9a4DCr1kWFW7ur97AF43 Za4Ut3yUK3Wvyw7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUPIb4IE77IF4wAFF20E14v26rWj6s0DM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28IrcIa0xkI8VA2jI8067AKxVWUXw A2048vs2IY020Ec7CjxVAFwI0_Xr0E3s1l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxS w2x7M28EF7xvwVC0I7IYx2IY67AKxVW7JVWDJwA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxV W8Jr0_Cr1UM28EF7xvwVC2z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I0E14v2 6rxl6s0DM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40Ex7xfMc Ij6xIIjxv20xvE14v26r1Y6r17McIj6I8E87Iv67AKxVW8Jr0_Cr1UMcvjeVCFs4IE7xkE bVWUJVW8JwACjcxG0xvY0x0EwIxGrwACI402YVCY1x02628vn2kIc2xKxwCY1x0262kKe7 AKxVWUtVW8ZwCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02 F40E14v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_Jw0_GF ylIxkGc2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7Cj xVAFwI0_Gr0_Cr1lIxAIcVCF04k26cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v26r 1j6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x07UJ xhLUUUUU= X-CM-SenderInfo: x2kh0wptl0x03j6k3tpzhluzxrxghudrp/ Content-Type: text/plain; charset="utf-8" From: Zheng Qixing When switching IO schedulers on a block device (e.g., loop0), blkcg_activate_policy() is called to allocate blkg_policy_data (pd) for all blkgs associated with that device's request queue. However, a race condition exists between blkcg_activate_policy() and concurrent blkcg deletion that leads to a use-after-free: T1 (blkcg_activate_policy): - Successfully allocates pd for blkg1 (loop0->queue, blkcgA) - Fails to allocate pd for blkg2 (loop0->queue, blkcgB) - Goes to enomem error path to rollback blkg1's resources T2 (blkcg deletion): - blkcgA is being deleted concurrently - blkg1 is freed via blkg_free_workfn() - blkg1->pd is freed T1 (continued): - In the rollback path, accesses pd->online after blkg1->pd has been freed - Triggers use-after-free The issue occurs because blkcg_activate_policy() doesn't hold adequate protection against concurrent blkg freeing during the error rollback path. The call trace is as follows: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D BUG: KASAN: slab-use-after-free in blkcg_activate_policy+0x516/0x5f0 Read of size 1 at addr ffff88802e1bc00c by task sh/7357 CPU: 1 PID: 7357 Comm: sh Tainted: G OE 6.6.0+ #1 Call Trace: blkcg_activate_policy+0x516/0x5f0 bfq_create_group_hierarchy+0x31/0x90 bfq_init_queue+0x6df/0x8e0 blk_mq_init_sched+0x290/0x3a0 elevator_switch+0x8a/0x190 elv_iosched_store+0x1f7/0x2a0 queue_attr_store+0xad/0xf0 kernfs_fop_write_iter+0x1ee/0x2e0 new_sync_write+0x154/0x260 vfs_write+0x313/0x3c0 ksys_write+0xbd/0x160 do_syscall_64+0x55/0x100 entry_SYSCALL_64_after_hwframe+0x78/0xe2 Allocated by task 7357: bfq_pd_alloc+0x6e/0x120 blkcg_activate_policy+0x141/0x5f0 bfq_create_group_hierarchy+0x31/0x90 bfq_init_queue+0x6df/0x8e0 blk_mq_init_sched+0x290/0x3a0 elevator_switch+0x8a/0x190 elv_iosched_store+0x1f7/0x2a0 queue_attr_store+0xad/0xf0 kernfs_fop_write_iter+0x1ee/0x2e0 new_sync_write+0x154/0x260 vfs_write+0x313/0x3c0 ksys_write+0xbd/0x160 do_syscall_64+0x55/0x100 entry_SYSCALL_64_after_hwframe+0x78/0xe2 Freed by task 14318: blkg_free_workfn+0x7f/0x200 process_one_work+0x2ef/0x5d0 worker_thread+0x38d/0x4f0 kthread+0x156/0x190 ret_from_fork+0x2d/0x50 ret_from_fork_asm+0x1b/0x30 Fix this bug by adding q->blkcg_mutex in the enomem branch of blkcg_activate_policy(). Fixes: f1c006f1c685 ("blk-cgroup: synchronize pd_free_fn() from blkg_free_w= orkfn() and blkcg_deactivate_policy()") Signed-off-by: Zheng Qixing Reviewed-by: Christoph Hellwig --- block/blk-cgroup.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 5e1a724a799a..af468676cad1 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1693,9 +1693,11 @@ int blkcg_activate_policy(struct gendisk *disk, cons= t struct blkcg_policy *pol) =20 enomem: /* alloc failed, take down everything */ + mutex_lock(&q->blkcg_mutex); spin_lock_irq(&q->queue_lock); blkcg_policy_teardown_pds(q, pol); spin_unlock_irq(&q->queue_lock); + mutex_unlock(&q->blkcg_mutex); ret =3D -ENOMEM; goto out; } --=20 2.39.2