From cb36e29bb0e4b0c33c3d5866a0a4aebace4c99b7 Mon Sep 17 00:00:00 2001 From: Krzysztof Sobota Date: Fri, 17 Jul 2020 12:31:09 +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. ------------[ 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") Reviewed-by: Guenter Roeck Reviewed-by: Alexander Sverdlin Signed-off-by: Krzysztof Sobota Link: https://lore.kernel.org/r/20200717103109.14660-1-krzysztof.sobota@nokia.com Signed-off-by: Guenter Roeck Signed-off-by: Wim Van Sebroeck --- 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 b277eebd377e..b7d750b24e49 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -994,6 +994,15 @@ 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_HARD); wd_data->timer.function = watchdog_timer_expired; @@ -1014,15 +1023,6 @@ 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);