From nobody Wed Feb 11 02:10:26 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 A3037136E3F; 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=1767837187; cv=none; b=hKBeDGtynnQJaWnkhdowWr3ptDBkpHkB2l6N02UczrTE3UdS+AxkqW2suTRwoDmrVsRizW8U7CMnS26gGw2farLaiKySNqwNNw3xEKFyvbCSlphwOhZsw9W1CHsn65JpIoPoG4IV/E2MQ34OnB0iTbjvlu8cxnPz+z4flECbFxY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767837187; c=relaxed/simple; bh=0/Y9yOEwzq8gMNbOAp62DRq10dZ05AoU8GAii37SP40=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=klHVxIwNWJXmo0fm74GzXrihPAgOpiCcEhbfzpm7O0r4YzOnyLT7nRAv5fV0f7ZasyUVS92pk1H6WjiwJZ324wz0X6ZqBnaDyZAlQle+EyaTkn7sydiT6dfNyOuCWJ/wi2P/s0KoEGiFWHB9VfMG9vlYd63wT5R7RBWkP/DobPQ= 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 [172.19.163.198]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4dmnw42MZLzKHMTj; 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 6EBC740574; 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--.41552S7; 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 3/3] blk-cgroup: skip dying blkg in blkcg_activate_policy() Date: Thu, 8 Jan 2026 09:44:16 +0800 Message-Id: <20260108014416.3656493-4-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--.41552S7 X-Coremail-Antispam: 1UD129KBjvJXoWxArWfuFWDZrWDXFW3AF4kCrg_yoW5KrWfpr Z5KryxCryDGFyDZan8t3WUXry8AF43JrW8JrWxKr4a9F43Aw18AFnrur1DGrWUCFWDAa15 Za1ktryDAa1UK3DanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUPIb4IE77IF4wAFF20E14v26rWj6s0DM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28IrcIa0xkI8VA2jI8067AKxVWUWw A2048vs2IY020Ec7CjxVAFwI0_Xr0E3s1l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxS w2x7M28EF7xvwVC0I7IYx2IY67AKxVW7JVWDJwA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxV W8Jr0_Cr1UM28EF7xvwVC2z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I0E14v2 6rxl6s0DM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40Ex7xfMc Ij6xIIjxv20xvE14v26r1Y6r17McIj6I8E87Iv67AKxVW8Jr0_Cr1UMcvjeVCFs4IE7xkE bVWUJVW8JwACjcxG0xvY0x0EwIxGrwACI402YVCY1x02628vn2kIc2xKxwCY1x0262kKe7 AKxVWUtVW8ZwCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02 F40E14v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_Jw0_GF ylIxkGc2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7Cj xVAFwI0_Gr0_Cr1lIxAIcVCF04k26cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v26r 1j6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x07Up c_-UUUUU= X-CM-SenderInfo: x2kh0wptl0x03j6k3tpzhluzxrxghudrp/ Content-Type: text/plain; charset="utf-8" From: Zheng Qixing When switching IO schedulers on a block device, blkcg_activate_policy() can race with concurrent blkcg deletion, leading to a use-after-free of the blkg. T1: T2: elv_iosched_store blkg_destroy elevator_switch kill(&blkg->refcnt) // blkg->refcnt=3D0 ... blkg_release // call_rcu blkcg_activate_policy __blkg_release list for blkg blkg_free blkg_free_workfn ->pd_free_fn(pd) blkg_get(blkg) // blkg->refcnt=3D0->1 list_del_init(&blkg->q_node) kfree(blkg) blkg_put(pinned_blkg) // blkg->refcnt=3D1->0 blkg_release // call_rcu again call_rcu(..., __blkg_release) Fix this by replacing blkg_get() with blkg_tryget(), which fails if the blkg's refcount has already reached zero. If blkg_tryget() fails, skip processing this blkg since it's already being destroyed. The uaf 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 rcu_accelerate_cbs+0x114/0x120 Read of size 8 at addr ffff88815a20b5d8 by task bash/1068 CPU: 0 PID: 1068 Comm: bash Not tainted 6.6.0-g6918ead378dc-dirty #31 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 = 04/01/2014 Call Trace: rcu_accelerate_cbs+0x114/0x120 rcu_report_qs_rdp+0x1fb/0x3e0 rcu_core+0x4d7/0x6f0 handle_softirqs+0x198/0x550 irq_exit_rcu+0x130/0x190 sysvec_apic_timer_interrupt+0x6e/0x90 asm_sysvec_apic_timer_interrupt+0x16/0x20 Allocated by task 1031: kasan_save_stack+0x1c/0x40 kasan_set_track+0x21/0x30 __kasan_kmalloc+0x8b/0x90 blkg_alloc+0xb6/0x9c0 blkg_create+0x8c6/0x1010 blkg_lookup_create+0x2ca/0x660 bio_associate_blkg_from_css+0xfb/0x4e0 bio_associate_blkg+0x62/0xf0 bio_init+0x272/0x8d0 bio_alloc_bioset+0x45a/0x760 ext4_bio_write_folio+0x68e/0x10d0 mpage_submit_folio+0x14a/0x2b0 mpage_process_page_bufs+0x1b1/0x390 mpage_prepare_extent_to_map+0xa91/0x1060 ext4_do_writepages+0x948/0x1c50 ext4_writepages+0x23f/0x4a0 do_writepages+0x162/0x5e0 filemap_fdatawrite_wbc+0x11a/0x180 __filemap_fdatawrite_range+0x9d/0xd0 file_write_and_wait_range+0x91/0x110 ext4_sync_file+0x1c1/0xaa0 __x64_sys_fsync+0x55/0x90 do_syscall_64+0x55/0x100 entry_SYSCALL_64_after_hwframe+0x78/0xe2 Freed by task 24: kasan_save_stack+0x1c/0x40 kasan_set_track+0x21/0x30 kasan_save_free_info+0x27/0x40 __kasan_slab_free+0x106/0x180 __kmem_cache_free+0x162/0x350 process_one_work+0x573/0xd30 worker_thread+0x67f/0xc30 kthread+0x28b/0x350 ret_from_fork+0x30/0x70 ret_from_fork_asm+0x1b/0x30 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 | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index af468676cad1..ac7702db0836 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1645,9 +1645,10 @@ int blkcg_activate_policy(struct gendisk *disk, cons= t struct blkcg_policy *pol) * GFP_NOWAIT failed. Free the existing one and * prealloc for @blkg w/ GFP_KERNEL. */ + if (!blkg_tryget(blkg)) + continue; if (pinned_blkg) blkg_put(pinned_blkg); - blkg_get(blkg); pinned_blkg =3D blkg; =20 spin_unlock_irq(&q->queue_lock); --=20 2.39.2