• Krzysztof Sobota's avatar
    watchdog: initialize device before misc_register · cb36e29b
    Krzysztof Sobota authored
    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: 72139dfa ("watchdog: Fix the race between the release of watchdog_core_data and cdev")
    Reviewed-by: default avatarGuenter Roeck <linux@roeck-us.net>
    Reviewed-by: default avatarAlexander Sverdlin <alexander.sverdlin@nokia.com>
    Signed-off-by: default avatarKrzysztof Sobota <krzysztof.sobota@nokia.com>
    Link: https://lore.kernel.org/r/20200717103109.14660-1-krzysztof.sobota@nokia.comSigned-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
    Signed-off-by: default avatarWim Van Sebroeck <wim@linux-watchdog.org>
    cb36e29b
watchdog_dev.c 29.8 KB