From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794435018; b=SzzXnFiCQUVuZeeErqNJwbZwr9MojU6y79+xhT37wqPEYJkZk9OROczSk+NDyAlghxBg VmmPfai4L9FY+FwYMykiHe2g0iSk+FKZWCHuz9BCGsrQVaea4DaF84bB1ja1mnsLFndWv uqZ7ZoZag9pp7/i30iUrdiM4H0bxnjq9UESBD/q74xxPSgxnKBMbpXv4FSi3btNMlWnok 1l/RJ6TUdtGO0YzYwO18j5DrPbKAzVZi861o2IcfHq3MTAbnx02k0q4A1gZ2xTM9Poyvq 7JIVzgmulcfgflrUmu3mWJX/RVp0a14vDYsJzXZqXr14/Ljlx9aquJlEpzMYIyufYVA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794435018; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=KpD0cjOWUMtVHZu3Vg/youUwxbjneyyuOQYPsEiKmM4=; b=VbmixvztMBkHDDKLWVpNlQU8TcnvcsUesz5W+S33LoF+2L9EK+fl2Da2m1aZKA3q0XCL 4lpnjaMGdCHOmcGVCNDjEQg7kDGWOgNyfSycuPWCTx1U1GnxiOy0m28l7O3sHnNRLC4uQ Aa5Mu10dqhCZFP1M40tUI2hLsxWoRcSz6/rQvLdEj06N/VJ2914Ehak/6GRp/az1Q9yn7 f/OBKE3973MFShEg9ZwPOV47C/RTn9nSMag0Ej7sCM8CG22iS1dg1Hz6pAYh0wzoh09Uo o9rZYihf2cjSUHSAF6HYpgpNwGjefNHuqxPFFrsm5KNz4djfub9CmD3MKjVubTgSFlg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=I0aLhJCz; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8A2DB606A31C for ; Wed, 11 Nov 2026 22:10:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=I0aLhJCz Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4F1521F00A06; Wed, 11 Nov 2026 22:10:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794435018; bh=KpD0cjOWUMtVHZu3Vg/youUwxbjneyyuOQYPsEiKmM4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=I0aLhJCzrrfn5IOYdE0v+epyHwxJBS2jgac1YXl7QMbHpptUTDL7ZHL9WVmqEO8LK Nax2G9J35eQTrg1nrEII7ow3wxQkd4+FzgAUsYxH9cv3yy1JI9btzf00gMqe/isMuy JbUD5oqthS3gdEMZlUVDl0g4wo763KAuW4p1nQLqw9wk7qDv2oNlE9cjKnkT6xy/q6 jpnWNXDxV2ilF220pDw/k1on/RrMq7vDdoC4QqmBfvnuxybsxBHB0MeOwE8p0gcaYT yawuMmiazN1C1X66KaYrXPrX6Y0L5j9soRHSFbauz7zaGaVDL+MM2khB8lwHU9qbK0 aPm4dC1/L3+1Q== From: Sasha Levin To: stable@vger.kernel.org Cc: Eklavya Singh , Andrew Morton , syzbot+5d4e96acd0febccb5e87@syzkaller.appspotmail.com, Joseph Qi , Mark Fasheh , Joel Becker , Heming Zhao , Deepanshu Kartikey , Cen Zhang , Sasha Levin Subject: [PATCH 6.12.y 2/2] ocfs2/heartbeat: serialize concurrent writes to a region's dev attribute Date: Wed, 11 Nov 2026 17:10:14 -0500 Message-ID: <20261111221006.4120209-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261111221006.4120209-1-sashal@kernel.org> References: <20261109200818-failed-6.12-0a8f258c0f01@kernel.org> <20261111221006.4120209-1-sashal@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Eklavya Singh [ Upstream commit 0a8f258c0f012314c36b9e4818cdc0178c68f891 ] 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(). The mutex is dropped while dev_store() waits for the heartbeat to become steady, which takes seconds, so a read of dev doesn't stall behind a start. hr_bdev_file is already set at that point, so other writers still get -EINVAL, and the cleanup after the wait retakes the mutex. With the patch the same test ran for 10 minutes with lockdep on and nothing was reported. So did a second one, with a working loop device, that interrupts starts during the wait while other threads read and write the attributes. Link: https://lore.kernel.org/20261020212339.46591-1-eklavyasingh2106@gmail.com Fixes: a7f6a5fb4bde ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem") Signed-off-by: Eklavya Singh Signed-off-by: Andrew Morton Reported-by: Closes: https://syzkaller.appspot.com/bug?extid=5d4e96acd0febccb5e87 Reviewed-by: Joseph Qi Cc: Mark Fasheh Cc: Joel Becker Cc: Heming Zhao Cc: Deepanshu Kartikey Cc: Cen Zhang Cc: Signed-off-by: Sasha Levin --- fs/ocfs2/cluster/heartbeat.c | 40 ++++++++++++++++++++++++++++++------ 1 file changed, 34 insertions(+), 6 deletions(-) diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c index c7fd2e5c2c0bf..85377208aa1ad 100644 --- a/fs/ocfs2/cluster/heartbeat.c +++ b/fs/ocfs2/cluster/heartbeat.c @@ -268,6 +268,8 @@ struct o2hb_region { struct list_head hr_handler_list; /* Serializes timeout arming against failed-start and teardown. */ struct mutex hr_arming_mutex; + /* Serializes the dev, block_bytes, start_block and blocks attributes. */ + struct mutex hr_dev_mutex; bool hr_stopping; /* last hb status, 0 for success, other value for error. */ @@ -1664,6 +1666,7 @@ 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; @@ -1693,6 +1696,7 @@ 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; @@ -1718,6 +1722,7 @@ static ssize_t o2hb_region_blocks_store(struct config_item *item, unsigned long tmp; char *p = (char *)page; + guard(mutex)(®->hr_dev_mutex); if (reg->hr_bdev_file) return -EINVAL; @@ -1735,10 +1740,12 @@ 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; } @@ -1856,11 +1863,9 @@ 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; @@ -1869,6 +1874,8 @@ static ssize_t o2hb_region_dev_store(struct config_item *item, ssize_t ret = -EINVAL; int live_threshold; + lockdep_assert_held(®->hr_dev_mutex); + if (reg->hr_bdev_file) return -EINVAL; @@ -1972,9 +1979,15 @@ static ssize_t o2hb_region_dev_store(struct config_item *item, wake_up_process(hb_task); + /* + * Don't hold hr_dev_mutex across the wait, which can take seconds. + * hr_bdev_file is already set, so other writers still get -EINVAL. + */ + mutex_unlock(®->hr_dev_mutex); ret = wait_event_interruptible(o2hb_steady_queue, atomic_read(®->hr_steady_iterations) == 0 || reg->hr_node_deleted); + mutex_lock(®->hr_dev_mutex); if (ret) { atomic_set(®->hr_steady_iterations, 0); reg->hr_aborted_start = 1; @@ -2028,6 +2041,20 @@ 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); @@ -2130,6 +2157,7 @@ static struct config_item *o2hb_heartbeat_group_make_item(struct config_group *g INIT_LIST_HEAD(®->hr_all_item); 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); -- 2.53.0