From: Krzysztof Sobota krzysztof.sobota@nokia.com
[ Upstream commit cb36e29bb0e4b0c33c3d5866a0a4aebace4c99b7 ]
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 [<c02126c4>] (unwind_backtrace) from [<c020da94>] (show_stack+0x18/0x1c) [<c020da94>] (show_stack) from [<c07f87d8>] (dump_stack+0xb4/0xe8) [<c07f87d8>] (dump_stack) from [<c0221f70>] (__warn+0xfc/0x114) [<c0221f70>] (__warn) from [<c0221fd8>] (warn_slowpath_fmt+0x50/0x74) [<c0221fd8>] (warn_slowpath_fmt) from [<c07fd394>] (kobject_get+0x50/0x54) [<c07fd394>] (kobject_get) from [<c0602ce8>] (get_device+0x1c/0x24) [<c0602ce8>] (get_device) from [<c06961e0>] (watchdog_open+0x90/0xf0) [<c06961e0>] (watchdog_open) from [<c06001dc>] (misc_open+0x130/0x17c) [<c06001dc>] (misc_open) from [<c0388228>] (chrdev_open+0xec/0x1a8) [<c0388228>] (chrdev_open) from [<c037fa98>] (do_dentry_open+0x204/0x3cc) [<c037fa98>] (do_dentry_open) from [<c0391e2c>] (path_openat+0x330/0x1148) [<c0391e2c>] (path_openat) from [<c0394518>] (do_filp_open+0x78/0xec) [<c0394518>] (do_filp_open) from [<c0381100>] (do_sys_open+0x130/0x1f4) [<c0381100>] (do_sys_open) from [<c0201000>] (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 [<c02126c4>] (unwind_backtrace) from [<c020da94>] (show_stack+0x18/0x1c) [<c020da94>] (show_stack) from [<c07f87d8>] (dump_stack+0xb4/0xe8) [<c07f87d8>] (dump_stack) from [<c0221f70>] (__warn+0xfc/0x114) [<c0221f70>] (__warn) from [<c0221fd8>] (warn_slowpath_fmt+0x50/0x74) [<c0221fd8>] (warn_slowpath_fmt) from [<c07fd368>] (kobject_get+0x24/0x54) [<c07fd368>] (kobject_get) from [<c0602ce8>] (get_device+0x1c/0x24) [<c0602ce8>] (get_device) from [<c06961e0>] (watchdog_open+0x90/0xf0) [<c06961e0>] (watchdog_open) from [<c06001dc>] (misc_open+0x130/0x17c) [<c06001dc>] (misc_open) from [<c0388228>] (chrdev_open+0xec/0x1a8) [<c0388228>] (chrdev_open) from [<c037fa98>] (do_dentry_open+0x204/0x3cc) [<c037fa98>] (do_dentry_open) from [<c0391e2c>] (path_openat+0x330/0x1148) [<c0391e2c>] (path_openat) from [<c0394518>] (do_filp_open+0x78/0xec) [<c0394518>] (do_filp_open) from [<c0381100>] (do_sys_open+0x130/0x1f4) [<c0381100>] (do_sys_open) from [<c0201000>] (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 linux@roeck-us.net Reviewed-by: Alexander Sverdlin alexander.sverdlin@nokia.com Signed-off-by: Krzysztof Sobota krzysztof.sobota@nokia.com Link: https://lore.kernel.org/r/20200717103109.14660-1-krzysztof.sobota@nokia.com Signed-off-by: Guenter Roeck linux@roeck-us.net Signed-off-by: Wim Van Sebroeck wim@linux-watchdog.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 c4147e93aa7d4..3729f99fd8eca 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -974,6 +974,15 @@ 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; @@ -994,15 +1003,6 @@ 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);