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Wed, 15 Jul 2020 08:09:25 -0700 (PDT) Subject: Re: [PATCH] watchdog: initialize device before misc_register To: "krzysztof.sobota@nokia.com" , wim@linux-watchdog.org, linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org Cc: alexander.sverdlin@nokia.com References: From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= Message-ID: Date: Wed, 15 Jul 2020 08:09:23 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/15/20 6:57 AM, krzysztof.sobota@nokia.com wrote: > From: Krzysztof Sobota > Date: Wed, 15 Jul 2020 13:13:42 +0200 > Subject: [PATCH] watchdog: initialize device before misc_register > > When watchdog device is being registered, it calls misc_register that > makes watchdog available for systemd to open. This is a data race > scenario, because when device is open it may still have device struct > not initialized - this in turn causes a crash. This patch moves > device initialization before misc_register call and it solves the > problem printed below. > A cleaner fix would probably be to move misc device registration after cdev registration, but then handling misc device registration failures would be much more complicated. With that, Reviewed-by: Guenter Roeck > ------------[ cut here ]------------ > WARNING: CPU: 3 PID: 1 at lib/kobject.c:612 kobject_get+0x50/0x54 > kobject: '(null)' ((ptrval)): is not initialized, yet kobject_get() is being called. > Modules linked in: k2_reset_status(O) davinci_wdt(+) sfn_platform_hwbcn(O) fsmddg_sfn(O) clk_misc_mmap(O) clk_sw_bcn(O) fsp_reset(O) cma_mod(O) slave_sup_notif(O) fpga_master(O) latency(O+) evnotify(O) enable_arm_pmu(O) xge(O) rio_mport_cdev br_netfilter bridge stp llc nvrd_checksum(O) ipv6 > CPU: 3 PID: 1 Comm: systemd Tainted: G           O 4.19.113-g2579778-fsm4_k2 #1 > Hardware name: Keystone > [] (unwind_backtrace) from [] (show_stack+0x18/0x1c) > [] (show_stack) from [] (dump_stack+0xb4/0xe8) > [] (dump_stack) from [] (__warn+0xfc/0x114) > [] (__warn) from [] (warn_slowpath_fmt+0x50/0x74) > [] (warn_slowpath_fmt) from [] (kobject_get+0x50/0x54) > [] (kobject_get) from [] (get_device+0x1c/0x24) > [] (get_device) from [] (watchdog_open+0x90/0xf0) > [] (watchdog_open) from [] (misc_open+0x130/0x17c) > [] (misc_open) from [] (chrdev_open+0xec/0x1a8) > [] (chrdev_open) from [] (do_dentry_open+0x204/0x3cc) > [] (do_dentry_open) from [] (path_openat+0x330/0x1148) > [] (path_openat) from [] (do_filp_open+0x78/0xec) > [] (do_filp_open) from [] (do_sys_open+0x130/0x1f4) > [] (do_sys_open) from [] (ret_fast_syscall+0x0/0x28) > Exception stack(0xd2ceffa8 to 0xd2cefff0) > ffa0:                   b6f69968 00000000 ffffff9c b6ebd210 000a0001 00000000 > ffc0: b6f69968 00000000 00000000 00000142 fffffffd ffffffff 00b65530 bed7bb78 > ffe0: 00000142 bed7ba70 b6cc2503 b6cc41d6 > ---[ end trace 7b16eb105513974f ]--- > > ------------[ cut here ]------------ > WARNING: CPU: 3 PID: 1 at lib/refcount.c:153 kobject_get+0x24/0x54 > refcount_t: increment on 0; use-after-free. > Modules linked in: k2_reset_status(O) davinci_wdt(+) sfn_platform_hwbcn(O) fsmddg_sfn(O) clk_misc_mmap(O) clk_sw_bcn(O) fsp_reset(O) cma_mod(O) slave_sup_notif(O) fpga_master(O) latency(O+) evnotify(O) enable_arm_pmu(O) xge(O) rio_mport_cdev br_netfilter bridge stp llc nvrd_checksum(O) ipv6 > CPU: 3 PID: 1 Comm: systemd Tainted: G        W  O 4.19.113-g2579778-fsm4_k2 #1 > Hardware name: Keystone > [] (unwind_backtrace) from [] (show_stack+0x18/0x1c) > [] (show_stack) from [] (dump_stack+0xb4/0xe8) > [] (dump_stack) from [] (__warn+0xfc/0x114) > [] (__warn) from [] (warn_slowpath_fmt+0x50/0x74) > [] (warn_slowpath_fmt) from [] (kobject_get+0x24/0x54) > [] (kobject_get) from [] (get_device+0x1c/0x24) > [] (get_device) from [] (watchdog_open+0x90/0xf0) > [] (watchdog_open) from [] (misc_open+0x130/0x17c) > [] (misc_open) from [] (chrdev_open+0xec/0x1a8) > [] (chrdev_open) from [] (do_dentry_open+0x204/0x3cc) > [] (do_dentry_open) from [] (path_openat+0x330/0x1148) > [] (path_openat) from [] (do_filp_open+0x78/0xec) > [] (do_filp_open) from [] (do_sys_open+0x130/0x1f4) > [] (do_sys_open) from [] (ret_fast_syscall+0x0/0x28) > Exception stack(0xd2ceffa8 to 0xd2cefff0) > ffa0:                   b6f69968 00000000 ffffff9c b6ebd210 000a0001 00000000 > ffc0: b6f69968 00000000 00000000 00000142 fffffffd ffffffff 00b65530 bed7bb78 > ffe0: 00000142 bed7ba70 b6cc2503 b6cc41d6 > ---[ end trace 7b16eb1055139750 ]--- > > Fixes: 72139dfa2464 ("watchdog: Fix the race between the release of watchdog_core_data and cdev") > Signed-off-by: Krzysztof Sobota > > Change-Id: I3b85f615d67ab5b8dc6c5c2dc42efd236d502d09 > --- >  drivers/watchdog/watchdog_dev.c | 18 +++++++++--------- >  1 file changed, 9 insertions(+), 9 deletions(-) > > diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c > index 10b2090f3e5e..1c322caecf7f 100644 > --- a/drivers/watchdog/watchdog_dev.c > +++ b/drivers/watchdog/watchdog_dev.c > @@ -947,6 +947,15 @@ static int watchdog_cdev_register(struct watchdog_device *wdd) >         if (IS_ERR_OR_NULL(watchdog_kworker)) >                 return -ENODEV; > > +       device_initialize(&wd_data->dev); > +       wd_data->dev.devt = MKDEV(MAJOR(watchdog_devt), wdd->id); > +       wd_data->dev.class = &watchdog_class; > +       wd_data->dev.parent = wdd->parent; > +       wd_data->dev.groups = wdd->groups; > +       wd_data->dev.release = watchdog_core_data_release; > +       dev_set_drvdata(&wd_data->dev, wdd); > +       dev_set_name(&wd_data->dev, "watchdog%d", wdd->id); > + >         kthread_init_work(&wd_data->work, watchdog_ping_work); >         hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); >         wd_data->timer.function = watchdog_timer_expired; > @@ -967,15 +976,6 @@ static int watchdog_cdev_register(struct watchdog_device *wdd) >                 } >         } > > -       device_initialize(&wd_data->dev); > -       wd_data->dev.devt = MKDEV(MAJOR(watchdog_devt), wdd->id); > -       wd_data->dev.class = &watchdog_class; > -       wd_data->dev.parent = wdd->parent; > -       wd_data->dev.groups = wdd->groups; > -       wd_data->dev.release = watchdog_core_data_release; > -       dev_set_drvdata(&wd_data->dev, wdd); > -       dev_set_name(&wd_data->dev, "watchdog%d", wdd->id); > - >         /* Fill in the data structures */ >         cdev_init(&wd_data->cdev, &watchdog_fops); > > -- > 2.14.0 >