From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-dl1-f48.google.com (mail-dl1-f48.google.com [74.125.82.48]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BABA048987A for ; Mon, 19 Oct 2026 07:30:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.48 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792395010; cv=none; b=VRYFN5tZD4I6bA0dzqhfYIrII4jOyFG9XgRtoD5rWpK2MJE/fRkajxD9LsuyncSLbb7mpA2QgxytWQdQsvIM+05xF+vQ8+vIl8LfSHIo2HajFmMJV+UxBKhmVwh+vFkxtAcGo8jgKE+RDTaHpaKpr8v5zfTC2il1PDHwfcmksd0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792395010; c=relaxed/simple; bh=KSLxsLECDBlglJ5ok09mHe2q8VxULP0ESynDUsj7NjM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Cx8t+4gKkN251RhQ41tswIfm5Tt3tBCDwFNhriDK8nBqLTX6M09IUYFkLakJvgfTB5F6Ogm0jawpahGoBXkjPLvUr1NZs/HZ79a7+54iz0xL88Cnoj5cPSAli4rrHvrc3WYBZSSjylE/QS9Z8ITegrOodd6qZ0fm6NdLGffQ7uc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=YEuLeHx+; arc=none smtp.client-ip=74.125.82.48 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="YEuLeHx+" Received: by mail-dl1-f48.google.com with SMTP id a92af1059eb24-15dd124bbe7so3353924c88.1 for ; Mon, 19 Oct 2026 00:30:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1792395008; x=1792999808; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to:content-type; bh=W7q+tRZEp7x1zsFqvPs4W277M15/fE06QNYP4aD/T7c=; b=YEuLeHx+oIDYF0/1zs0ioFged4Rid3sTaRson+OVR/O/l3fgz5++mImkgtx4AfMjfR SypSb3MxBgv5LzQzRRRicI9LNbRYNloaMkt0jSsddSk+SPG7yUNCj84xwoEredJaJwhd xBhJ+9fxyT7iO8Sgq7v57XxlnXB64E7LHtxBO2IRczqUkoJCM4HaQZgSu+tidQDz6Wzk rUB5pK8SIRpVMem2bX2hXiSOmK08baUt02nCvRgQyGGsNEt1JS3l7WHh8dmtmgjNnrG9 opf0F466B7ahWHi4VMDqCZHlRLLmTyd/CSAFK400Q6ixNxmZlCFCxG6iVcGsXyScxpSh ABjA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1792395008; x=1792999808; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to:content-type; bh=W7q+tRZEp7x1zsFqvPs4W277M15/fE06QNYP4aD/T7c=; b=NzkWCAWXqAtW6kHwymlzG4OQVuW7Oy2JfYrmgKV2P7O7ioxeWow3kmRFiv6MN+0hhk CqTS+LageTZPxgioFKQF4e0KKkIyfO5Hv4i3P3J4UboNMZ8hwGw6ZJ4bPH4XejYnh5go 47/Z+cYMmBKHypXUx0LSMt4HP9ealVbTNa3gkEINw6Q1wpdDQnOwZ8IXYBz9TVN+//rH LsrwQ7LjlTeN/HkPBufKeROhHV58+unS0gUTAy9CNsElAzioPTGuXjqZGQ/x4L6CjMPK XqW+ixcfppvAGwy4nTpoOIB2tT3li7TwCLgQYIOUm6EJuaCQqQjtMvtiRZeJv4v+2RSP wdDg== X-Forwarded-Encrypted: i=1; AKwUvBxUbkCmB/yUc0vOEBE72bTAMl5oWOaAkrJAlgfW/Jfcp3LMOoakQ9bBs0+8wqO36i6cKcjNCq0=@vger.kernel.org X-Gm-Message-State: AFq9FYK9ZardX1ab1RpdOVeF+zWyAqrTFA/X3wBRaLXQ1xOzEMszXhkm BD6IPWnSecDmfThzUO+6OIf4EvBYtPBURZnzobAWDvUicSruws/KQvvw X-Gm-Gg: AYBFou3sQyXw2EnaDSDLwE3ATfgJkuKDpthO25CJQyWc7cbbUGxFOUS5pvPkLtKYoVc UmguyD5t9NF453lmifN2Eyjop2r/GGSRu/HL7MseqJzxWVIVA8sS9CW9N07L7f1ORT6fNZ1nxlz dYVyWg+yqN8YuVCt2HRvgGrVuVqAzeOiX7MqmOpZPpyYOqsW7991Wt3FhL6t06JakSPBufXjMZV zrNTk+7TKsXaNAuVElFA/ME+0uqx176C7ofT9IwNS391MSFaYXFhMXk8/praXbjST923CQw9Plp hp3rmbkFUmFDcdT12vib0z7sKKpe/hn7CYYbpb2MyQyffpQMdrvreFeHMMr+xVTrPLsXQbJMqzl B1JtptEKR+BfhNJW+jBBN8l1r2hpOeL6/M6dIMHm07rdmVLS34R18hAV3R8bKwf62h12GYVT1k4 QDKGoaoh9aQZlCKPHFGafMStxY7DCqO/rtUehKYsL+pmUFAaGnn5IO4GnE0XrsEM1pcdNp6/Msj qdR48LRdG+NMQnwycMygnlgyOxIwp5kCUwi3TiqifvnKq/IWdveuzX3scV4TNNXT4tMZ04NXjdK QkESsg== X-Received: by 2002:a05:701a:ca05:b0:17e:6de6:6a1a with SMTP id a92af1059eb24-18511ad9debmr11070852c88.8.1792395007422; Mon, 19 Oct 2026 00:30:07 -0700 (PDT) Received: from codespaces-393231.mimvmn1ww3huhhjmzljqefhnig.rx.internal.cloudapp.net ([4.240.39.204]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1831b75be5esm35134155c88.16.2026.10.19.00.30.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Oct 2026 00:30:06 -0700 (PDT) From: Eklavya Singh To: Mark Fasheh , Joel Becker , Joseph Qi Cc: Heming Zhao , Andrew Morton , ocfs2-devel@lists.linux.dev, linux-kernel@vger.kernel.org, Eklavya Singh , syzbot+5d4e96acd0febccb5e87@syzkaller.appspotmail.com, stable@vger.kernel.org Subject: [PATCH v2] ocfs2/heartbeat: serialize concurrent writes to a region's dev attribute Date: Mon, 19 Oct 2026 07:29:35 +0000 Message-ID: <20261019072936.2279-1-eklavyasingh2106@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20261018163121.128911-1-eklavyasingh2106@gmail.com> References: <20261018163121.128911-1-eklavyasingh2106@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit o2hb_region_dev_store() checks reg->hr_bdev_file to see if the region is already started, but nothing stops two writers from doing that at the same time. configfs only serializes writes through the same open file, so two processes that each open the dev attribute can both get past the check: A: hr_bdev_file is NULL, opens file A, sets hr_bdev_file = A B: hr_bdev_file is NULL, opens file B, sets hr_bdev_file = B A: start fails, fput(hr_bdev_file) drops B, sets it to NULL B: start fails, fput(NULL) Both calls also use the same hr_slots, hr_slot_data and hr_tmp_block, so the error paths can free the slot data twice. syzbot hit the fput(NULL) with an unbound loop device, where every start fails with -EIO. With four threads doing the same thing on a KASAN kernel I get both crashes within a second: BUG: KASAN: double-free in o2hb_unmap_slot_data+0x14d/0x2f0 BUG: kernel NULL pointer dereference, address: 0000000000000158 Add a mutex to the region and hold it in dev_store(), in the block_bytes, start_block and blocks stores, and in dev_show(), since they all look at hr_bdev_file. dev_store() cleans up with goto, so it takes the mutex in a small wrapper rather than with guard(). It sleeps with the mutex held while it waits for the heartbeat thread. That is fine because neither the thread nor the teardown paths take it. With the patch the same test ran for 10 minutes with lockdep on and nothing was reported. Fixes: a7f6a5fb4bde ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem") Reported-by: syzbot+5d4e96acd0febccb5e87@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=5d4e96acd0febccb5e87 Cc: stable@vger.kernel.org Signed-off-by: Eklavya Singh --- v2: take the mutex in a wrapper around dev_store() instead of with guard(), since dev_store() uses goto for its cleanup. No other changes. v1: https://lore.kernel.org/all/20261018163121.128911-1-eklavyasingh2106@gmail.com/ fs/ocfs2/cluster/heartbeat.c | 32 ++++++++++++++++++++++++++------ 1 file changed, 26 insertions(+), 6 deletions(-) diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c index 1c3def99bb0..003c398366e 100644 --- a/fs/ocfs2/cluster/heartbeat.c +++ b/fs/ocfs2/cluster/heartbeat.c @@ -269,6 +269,8 @@ struct o2hb_region { struct list_head hr_handler_list; /* Serializes timeout arming against failed-start and teardown. */ struct mutex hr_arming_mutex; + /* Serializes the region's configfs attributes against dev_store(). */ + struct mutex hr_dev_mutex; bool hr_stopping; /* last hb status, 0 for success, other value for error. */ @@ -1676,6 +1678,7 @@ static ssize_t o2hb_region_block_bytes_store(struct config_item *item, unsigned long block_bytes; unsigned int block_bits; + guard(mutex)(®->hr_dev_mutex); if (reg->hr_bdev_file) return -EINVAL; @@ -1705,6 +1708,7 @@ static ssize_t o2hb_region_start_block_store(struct config_item *item, char *p = (char *)page; ssize_t ret; + guard(mutex)(®->hr_dev_mutex); if (reg->hr_bdev_file) return -EINVAL; @@ -1731,6 +1735,7 @@ static ssize_t o2hb_region_blocks_store(struct config_item *item, char *p = (char *)page; int ret; + guard(mutex)(®->hr_dev_mutex); if (reg->hr_bdev_file) return -EINVAL; @@ -1748,10 +1753,12 @@ static ssize_t o2hb_region_blocks_store(struct config_item *item, static ssize_t o2hb_region_dev_show(struct config_item *item, char *page) { + struct o2hb_region *reg = to_o2hb_region(item); unsigned int ret = 0; - if (to_o2hb_region(item)->hr_bdev_file) - ret = sprintf(page, "%pg\n", reg_bdev(to_o2hb_region(item))); + guard(mutex)(®->hr_dev_mutex); + if (reg->hr_bdev_file) + ret = sprintf(page, "%pg\n", reg_bdev(reg)); return ret; } @@ -1867,11 +1874,9 @@ static int o2hb_populate_slot_data(struct o2hb_region *reg) * this is acting as commit; we set up all of hr_bdev_file and hr_task or * nothing */ -static ssize_t o2hb_region_dev_store(struct config_item *item, - const char *page, - size_t count) +static ssize_t __o2hb_region_dev_store(struct o2hb_region *reg, + const char *page, size_t count) { - struct o2hb_region *reg = to_o2hb_region(item); struct task_struct *hb_task; long fd; int sectsize; @@ -2032,6 +2037,20 @@ static ssize_t o2hb_region_dev_store(struct config_item *item, return ret; } +static ssize_t o2hb_region_dev_store(struct config_item *item, + const char *page, + size_t count) +{ + struct o2hb_region *reg = to_o2hb_region(item); + ssize_t ret; + + mutex_lock(®->hr_dev_mutex); + ret = __o2hb_region_dev_store(reg, page, count); + mutex_unlock(®->hr_dev_mutex); + + return ret; +} + static ssize_t o2hb_region_pid_show(struct config_item *item, char *page) { struct o2hb_region *reg = to_o2hb_region(item); @@ -2156,6 +2175,7 @@ static struct config_item *o2hb_heartbeat_group_make_item(struct config_group *g reg->hr_key = crc32_le(reg->hr_region_num + O2NM_MAX_REGIONS, name, strlen(name)); mutex_init(®->hr_arming_mutex); + mutex_init(®->hr_dev_mutex); reg->hr_stopping = true; INIT_DELAYED_WORK(®->hr_write_timeout_work, o2hb_write_timeout); INIT_DELAYED_WORK(®->hr_nego_timeout_work, o2hb_nego_timeout); -- 2.55.0