From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D4DA8C4332F for ; Thu, 10 Nov 2022 02:37:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232226AbiKJChA (ORCPT ); Wed, 9 Nov 2022 21:37:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45222 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232213AbiKJCg7 (ORCPT ); Wed, 9 Nov 2022 21:36:59 -0500 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B3D19201BD; Wed, 9 Nov 2022 18:36:57 -0800 (PST) Received: from kwepemi500024.china.huawei.com (unknown [172.30.72.57]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4N75W54m3ZzJnZQ; Thu, 10 Nov 2022 10:33:53 +0800 (CST) Received: from [10.174.179.163] (10.174.179.163) by kwepemi500024.china.huawei.com (7.221.188.100) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Thu, 10 Nov 2022 10:36:54 +0800 Message-ID: Date: Thu, 10 Nov 2022 10:36:53 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.1.2 Subject: Re: [PATCH v2] gpiolib: fix memory leak in gpiochip_setup_dev Content-Language: en-US To: Kent Gibson , Andy Shevchenko , CC: , , , , , Linux Kernel Mailing List References: <20221109093120.3128541-1-zengheng4@huawei.com> From: Zeng Heng In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.163] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemi500024.china.huawei.com (7.221.188.100) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On 2022/11/10 9:26, Kent Gibson wrote: > On Wed, Nov 09, 2022 at 04:47:08PM +0200, Andy Shevchenko wrote: >> On Wed, Nov 09, 2022 at 05:31:20PM +0800, Zeng Heng wrote: >>> gcdev_register & gcdev_unregister call device_add & device_del to >>> request/release source. But in device_add, the dev->p allocated by >>> device_private_init is not released by device_del. >> First of all, we refer to the functions like func(). Thanks, it would be updated in next version. > Further to this, the description of the problem could be clearer - > it would be helpful to indicate the code path that triggers the problem > - it is gpiochip_sysfs_register() returning an error? > >>> So when calling gcdev_unregister to release gdev, it needs put_device >>> to release dev in the following. >>> >>> Otherwise, kmemleak would report memory leak such as below: >>> >>> unreferenced object 0xffff88810b406400 (size 512): >>> comm "python3", pid 1682, jiffies 4295346908 (age 24.090s) >>> hex dump (first 32 bytes): >>> 00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00 .....N.......... >>> ff ff ff ff ff ff ff ff a0 5e 23 90 ff ff ff ff .........^#..... >>> backtrace: >> Second, read Submitting Patches on how to provide your backtraces in the >> message body. Thanks, it would be updated in next version. >> >>> [<00000000a58ee5fe>] kmalloc_trace+0x22/0x110 >>> [<0000000045fe2058>] device_add+0xb34/0x1130 >>> [<00000000d778b45f>] cdev_device_add+0x83/0xe0 >>> [<0000000089f948ed>] gpiolib_cdev_register+0x73/0xa0 >>> [<00000000a3a8a316>] gpiochip_setup_dev+0x1c/0x70 >>> [<00000000787227b4>] gpiochip_add_data_with_key+0x10f6/0x1bf0 >>> [<000000009ac5742c>] devm_gpiochip_add_data_with_key+0x2e/0x80 >>> [<00000000bf2b23d9>] xra1403_probe+0x192/0x1b0 [gpio_xra1403] >>> [<000000005b5ef2d4>] spi_probe+0xe1/0x140 >>> [<000000002b26f6f1>] really_probe+0x17c/0x3f0 >>> [<00000000dd2dad9c>] __driver_probe_device+0xe3/0x170 >>> [<000000005ca60d2a>] device_driver_attach+0x34/0x80 >>> [<00000000e9db90db>] bind_store+0x10b/0x1a0 >>> [<00000000e2650f8a>] drv_attr_store+0x49/0x70 >>> [<0000000080a80b2b>] sysfs_kf_write+0x8c/0xb0 >>> [<00000000a28b45b9>] kernfs_fop_write_iter+0x216/0x2e0 >>> >>> unreferenced object 0xffff888100de9800 (size 512): >>> comm "python3", pid 264, jiffies 4294737615 (age 33.514s) >>> hex dump (first 32 bytes): >>> 00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00 .....N.......... >>> ff ff ff ff ff ff ff ff a0 5e 63 a1 ff ff ff ff .........^c..... >>> backtrace: >>> [<00000000bcc571d0>] kmalloc_trace+0x22/0x110 >>> [<00000000eeb06124>] device_add+0xb34/0x1130 >>> [<000000007e5cd2fd>] cdev_device_add+0x83/0xe0 >>> [<000000008f6bcd3a>] gpiolib_cdev_register+0x73/0xa0 >>> [<0000000012c93b24>] gpiochip_setup_dev+0x1c/0x70 >>> [<00000000a24b646a>] gpiochip_add_data_with_key+0x10f6/0x1bf0 >>> [<000000000c225212>] tpic2810_probe+0x16e/0x196 [gpio_tpic2810] >>> [<00000000b52d04ff>] i2c_device_probe+0x651/0x680 >>> [<0000000058d3ff6b>] really_probe+0x17c/0x3f0 >>> [<00000000586f43d3>] __driver_probe_device+0xe3/0x170 >>> [<000000003f428602>] device_driver_attach+0x34/0x80 >>> [<0000000040e91a1b>] bind_store+0x10b/0x1a0 >>> [<00000000c1d990b9>] drv_attr_store+0x49/0x70 >>> [<00000000a23bfc22>] sysfs_kf_write+0x8c/0xb0 >>> [<00000000064e6572>] kernfs_fop_write_iter+0x216/0x2e0 >>> [<00000000026ce093>] vfs_write+0x658/0x810 >>> >>> Because at the point of gpiochip_setup_dev here, where dev.release >>> does not set yet, calling put_device would cause the warning of >>> no release function and double-free in the following fault handler >>> route (when kfree dev_name). So directly calling kfree to release >>> dev->p here in case of memory leak. > Again, this could be clearer. The dev->p is normally freed by > device_release() - why is that not happening in this case? > (as put_device() is never called in this path) > > The double free you see if you do call put_device() appears to be due to > different expectations as to the cleanup that gpiochip_setup_dev() will > perform on error, depending on where it is called. gpiochip_setup_devs() > assumes any cleanup is performed by gpiochip_setup_dev(), while > gpiochip_add_data_with_key() assumes that it hasn't performed any cleanup. > > Having gpiochip_setup_dev() perform its own cleanup makes the most sense > to me, so gpiochip_add_data_with_key() should be changed to allow for > that. Right, the cleanup route of gpiochip_add_data_with_key() & gpiochip_setup_dev() has to be considered comprehensively after any possible cases of fault injections. >> ... >> >>> @@ -539,6 +539,7 @@ static int gpiochip_setup_dev(struct gpio_device *gdev) >>> >>> err_remove_device: >>> gcdev_unregister(gdev); >>> + kfree(gdev->dev.p); >>> return ret; >> Third, I do not believe it's a correct fix. >> Have you read comments around device_del() / etc.? Yes, not only the comments I read, but also the device_del() implement code. Releasing the dev->p pointer is not the business with device_del(), but it's relied on put_device() calling release function. Turning back here, the release function is not set yet at this point, there is a gap between device_add() and set release function pointer. That's the reason why choose to free dev->p explicitly as the mail mentioned above. > I agree - this is not the correct fix. The correct fix is to trigger the > normal cleanup mechanism, so put_device(). > The fact that that triggers a warning: > > "Device '%s' does not have a release() function, it is broken and must be > fixed. See Documentation/core-api/kobject.rst.\n" > > is an indicator that dev.release should be set earlier. > If gpiodevice_release() is not appropriate, or cannot be modified to deal > with the device state at that point, then an appropriate interim release > function should be set. > > And, as mentioned above, gpiochip_add_data_with_key() needs to be modified > to allow for gpiochip_setup_dev() cleaning up its own mess. > > That is my take, but that is just from perusing the code so I may be > totally off base. Either way, an ACK/NACK on this from a maintainer or > other gpiolib expert would be helpful to expiditing a solution. > > Cheers, > Kent. Yes, exactly. Thanks to all, Zeng Heng