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=1794063216; b=4wNpcwt5esU38qkWqgOWj+EHaLVkUDtIsLnw2Z/Ak5l20Cv3mM6eruVKL7JknrJZaC9M qkRUVo5VnCgV3wsU38BIxkH5VaUuNO9m9xnXqXPLvwf/jLFK8oUmlG75bKBtcYkE7/YyJ tkjs5zZGdU6LE2Tqp9QBtZRru7L2yG9a3qG308Nps8GVKT+Sen1NcccQZ5IT/2u3sLrSd EzIMmeCviRVgoAid2xJDY/3DK/ccJKOpg/8Ds2PwNA3e/68b6nwvRtH4U7JYItDOsyxqg sXwMgZnDqI3GWhqL8YNG/y4zf0J5MlNJTb2XYdYArMXlMJt4I9NxfSdk2cuG841EYGw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794063216; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=bJ+EH6PlFGaTqgIw+w3Ft5igP555xfLVErY0OCXypnc=; b=1UsVdKYDGn/s8oOhvCS3+SwxRgSL4AIRrz+5ELCS7OkhrOYn9hL8DS250Sh3P+x/dHZB lZQKU31ORRdYUboLOXNk75ko8zgVZ1eCRacXrvSQPpjkRhXRW9S5PiULjee2OstfKV+82 cSWNLb1QCfd/GR3dvGqWkEVevJ9bWJHUyTL0X7Ppd35wbJsROWPBF5grJ/rOb3+EIJ0aQ gZ0OAI3oFlxT3I/mhaAYLJG9d+u2ceTxEsNBZi1LhoipXrE+ehhKOrV4+v/Ima621/brd YApeDsEOekrQhWRB0hhMecDw92q8eIGT7yuQKZVx5o10MEnLEoi4ho3NFlkFWRndCYw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=CLfOSOQe; 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 0C722606A326; Sat, 7 Nov 2026 14:53:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=CLfOSOQe Received: by smtp.kernel.org (Postfix) with ESMTPSA id AFC971F0089F; Sat, 7 Nov 2026 14:53:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794063215; bh=bJ+EH6PlFGaTqgIw+w3Ft5igP555xfLVErY0OCXypnc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=CLfOSOQeXJnA5I1ef0bkxDLXu/NPbm+dq1ZsjbVf3Bzuau+dQa5JlLFfVmp9cPTX+ L0a6IzGmazbsUeGV6Q6k8wrgD4Ld93bjGxnycvlgFIsh/uJZOGKAxTIGEDDCqtEW6j AjwGneSKwb42y9+bcKK9D+aLw1AWPEctuHxAQ9/w= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+95eeb4ada2349a2170ea@syzkaller.appspotmail.com, Yu Kuai , Yogesh Gaur , Sasha Levin Subject: [PATCH 6.18 425/869] md: dont hand out the array before md_alloc() has added mddev->kobj Date: Sat, 7 Nov 2026 08:51:47 -0500 Message-ID: <20261107134908.259178381@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261107134852.069646174@linuxfoundation.org> References: <20261107134852.069646174@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore 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 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yogesh Gaur [ Upstream commit d1472ca2ca5de8ecd2b358411eb14c031404ecf0 ] md_alloc() publishes the gendisk before it is done setting the mddev up: disk->private_data = mddev; ... error = add_disk(disk); if (error) goto out_put_disk; kobject_init(&mddev->kobj, &md_ktype); error = kobject_add(&mddev->kobj, &disk_to_dev(disk)->kobj, "%s", "md"); add_disk() makes /dev/mdN openable. mddev comes from mddev_alloc() and is zeroed, so anything that gets in between add_disk() and kobject_add() sees an mddev->kobj that has never been through kobject_init() - no ktype, no kref, state_initialized clear. syzbot opens the array in that window and issues ADD_NEW_DISK: kobject: '(null)' (ffff8880120640f0): is not initialized, yet kobject_get() is being called. WARNING: lib/kobject.c:642 at kobject_add_internal+0xea/0xcd0 lib/kobject.c:225 kobject_add_varg lib/kobject.c:374 [inline] kobject_add+0x163/0x240 lib/kobject.c:426 bind_rdev_to_array+0x80c/0xdd0 drivers/md/md.c:2621 md_add_new_disk+0xe3b/0x1850 drivers/md/md.c:7684 md_ioctl+0x200a/0x2610 drivers/md/md.c:8499 bind_rdev_to_array() is not the only way in. md_run() calls sysfs_create_group(&mddev->kobj, &md_redundancy_group), and internal_create_group() has its own WARN_ON(!kobj->sd), so RUN_ARRAY in the same window warns too. Every ioctl that can reach mddev->kobj runs under reconfig_mutex, so hold it across add_disk() and kobject_add(). An ioctl issued in the window now waits for md_alloc() to finish instead of seeing a half-built mddev, and opening the array still succeeds. The ioctls md_ioctl() serves without the mutex only read array state and return -ENODEV on an array with no disks. Hoisting kobject_init() above add_disk() is not an option: commit ca39f7502425 ("md: fix mddev->kobj lifetime") moved it below add_disk() so that md_alloc()'s error paths, which free the mddev directly, never see an initialised kobject. Fixes: ca39f7502425 ("md: fix mddev->kobj lifetime") Reported-by: syzbot+95eeb4ada2349a2170ea@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6aaf3284.514bccd6.255447.0003.GAE@google.com/ Suggested-by: Yu Kuai Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Yogesh Gaur Link: https://patch.msgid.link/20261006122904.1538-1-yogeshgaur.83@gmail.com Signed-off-by: Yu Kuai Signed-off-by: Sasha Levin --- drivers/md/md.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/drivers/md/md.c b/drivers/md/md.c index 8d9e111939f64..937a2f4da84ba 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -6258,12 +6258,22 @@ struct mddev *md_alloc(dev_t dev, char *name) disk->events |= DISK_EVENT_MEDIA_CHANGE; mddev->gendisk = disk; + + /* + * add_disk() makes the array openable before mddev->kobj exists. + * Hold reconfig_mutex until kobject_add() is done so that ioctls + * issued in between wait instead of using an uninitialised kobj. + */ + mddev_lock_nointr(mddev); error = add_disk(disk); - if (error) + if (error) { + mddev_unlock(mddev); goto out_put_disk; + } kobject_init(&mddev->kobj, &md_ktype); error = kobject_add(&mddev->kobj, &disk_to_dev(disk)->kobj, "%s", "md"); + mddev_unlock(mddev); if (error) { /* * The disk is already live at this point. Clear the hold flag -- 2.53.0