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SubjectRe: [PATCH] watchdog: fix UAF in reboot notifier handling in watchdog core code
On Wed, Jan 08, 2020 at 01:53:47PM +0100, Vladis Dronov wrote:
> After the commit 44ea39420fc9 ("drivers/watchdog: make use of
> devm_register_reboot_notifier()") the struct notifier_block reboot_nb in
> the struct watchdog_device is removed from the reboot notifiers chain at
> the time watchdog's chardev is closed. But at least in i6300esb.c case
> reboot_nb is embedded in the struct esb_dev which can be freed on its
> device removal and before the chardev is closed, thus UAF at reboot:
>
> [ 7.728581] esb_probe: esb_dev.watchdog_device ffff91316f91ab28
> ts# uname -r note the address ^^^
> 5.5.0-rc5-ae6088-wdog
> ts# ./openwdog0 &
> [1] 696
> ts# opened /dev/watchdog0, sleeping 10s...
> ts# echo 1 > /sys/devices/pci0000\:00/0000\:00\:09.0/remove
> [ 178.086079] devres:rel_nodes: dev ffff91317668a0b0 data ffff91316f91ab28
> esb_dev.watchdog_device.reboot_nb memory is freed here ^^^
> ts# ...woken up
> [ 181.459010] devres:rel_nodes: dev ffff913171781000 data ffff913174a1dae8
> [ 181.460195] devm_unreg_reboot_notifier: res ffff913174a1dae8 nb ffff91316f91ab78
> attempt to use memory already freed ^^^
> [ 181.461063] devm_unreg_reboot_notifier: nb->call 6b6b6b6b6b6b6b6b
> [ 181.461243] devm_unreg_reboot_notifier: nb->next 6b6b6b6b6b6b6b6b
> freed memory is filled with a slub poison ^^^
> [1]+ Done ./openwdog0
> ts# reboot
> [ 229.921862] systemd-shutdown[1]: Rebooting.
> [ 229.939265] notifier_call_chain: nb ffffffff9c6c2f20 nb->next ffffffff9c6d50c0
> [ 229.943080] notifier_call_chain: nb ffffffff9c6d50c0 nb->next 6b6b6b6b6b6b6b6b
> [ 229.946054] notifier_call_chain: nb 6b6b6b6b6b6b6b6b INVAL
> [ 229.957584] general protection fault: 0000 [#1] SMP
> [ 229.958770] CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 5.5.0-rc5-ae6088-wdog
> [ 229.960224] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), ...
> [ 229.963288] RIP: 0010:notifier_call_chain+0x66/0xd0
> [ 229.969082] RSP: 0018:ffffb20dc0013d88 EFLAGS: 00010246
> [ 229.970812] RAX: 000000000000002e RBX: 6b6b6b6b6b6b6b6b RCX: 00000000000008b3
> [ 229.972929] RDX: 0000000000000000 RSI: 0000000000000096 RDI: ffffffff9ccc46ac
> [ 229.975028] RBP: 0000000000000001 R08: 0000000000000000 R09: 00000000000008b3
> [ 229.977039] R10: 0000000000000001 R11: ffffffff9c26c740 R12: 0000000000000000
> [ 229.979155] R13: 6b6b6b6b6b6b6b6b R14: 0000000000000000 R15: 00000000fffffffa
> ... slub_debug=FZP poison ^^^
> [ 229.989089] Call Trace:
> [ 229.990157] blocking_notifier_call_chain+0x43/0x59
> [ 229.991401] kernel_restart_prepare+0x14/0x30
> [ 229.992607] kernel_restart+0x9/0x30
> [ 229.993800] __do_sys_reboot+0x1d2/0x210
> [ 230.000149] do_syscall_64+0x3d/0x130
> [ 230.001277] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 230.002639] RIP: 0033:0x7f5461bdd177
> [ 230.016402] Modules linked in: i6300esb
> [ 230.050261] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
>
> Fix the crash by reverting 44ea39420fc9 so unregister_reboot_notifier()
> is called when watchdog device is removed. This also makes handling of
> the reboot notifier unified with the handling of the restart handler,
> which is freed with unregister_restart_handler() in the same place.
>
> Fixes: 44ea39420fc9 ("drivers/watchdog: make use of devm_register_reboot_notifier()")
> Cc: stable@vger.kernel.org # v4.15+
> Signed-off-by: Vladis Dronov <vdronov@redhat.com>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
> drivers/watchdog/watchdog_core.c | 35 +++++++++++++++++++++++++++++++
> drivers/watchdog/watchdog_dev.c | 36 +-------------------------------
> 2 files changed, 36 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index 21e8085b848b..861daf4f37b2 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -147,6 +147,25 @@ int watchdog_init_timeout(struct watchdog_device *wdd,
> }
> EXPORT_SYMBOL_GPL(watchdog_init_timeout);
>
> +static int watchdog_reboot_notifier(struct notifier_block *nb,
> + unsigned long code, void *data)
> +{
> + struct watchdog_device *wdd;
> +
> + wdd = container_of(nb, struct watchdog_device, reboot_nb);
> + if (code == SYS_DOWN || code == SYS_HALT) {
> + if (watchdog_active(wdd)) {
> + int ret;
> +
> + ret = wdd->ops->stop(wdd);
> + if (ret)
> + return NOTIFY_BAD;
> + }
> + }
> +
> + return NOTIFY_DONE;
> +}
> +
> static int watchdog_restart_notifier(struct notifier_block *nb,
> unsigned long action, void *data)
> {
> @@ -235,6 +254,19 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
> }
> }
>
> + if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status)) {
> + wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;
> +
> + ret = register_reboot_notifier(&wdd->reboot_nb);
> + if (ret) {
> + pr_err("watchdog%d: Cannot register reboot notifier (%d)\n",
> + wdd->id, ret);
> + watchdog_dev_unregister(wdd);
> + ida_simple_remove(&watchdog_ida, id);
> + return ret;
> + }
> + }
> +
> if (wdd->ops->restart) {
> wdd->restart_nb.notifier_call = watchdog_restart_notifier;
>
> @@ -289,6 +321,9 @@ static void __watchdog_unregister_device(struct watchdog_device *wdd)
> if (wdd->ops->restart)
> unregister_restart_handler(&wdd->restart_nb);
>
> + if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status))
> + unregister_reboot_notifier(&wdd->reboot_nb);
> +
> watchdog_dev_unregister(wdd);
> ida_simple_remove(&watchdog_ida, wdd->id);
> }
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 4b2a85438478..8b5c742f24e8 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -38,7 +38,6 @@
> #include <linux/miscdevice.h> /* For handling misc devices */
> #include <linux/module.h> /* For module stuff/... */
> #include <linux/mutex.h> /* For mutexes */
> -#include <linux/reboot.h> /* For reboot notifier */
> #include <linux/slab.h> /* For memory functions */
> #include <linux/types.h> /* For standard types (like size_t) */
> #include <linux/watchdog.h> /* For watchdog specific items */
> @@ -1097,25 +1096,6 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
> put_device(&wd_data->dev);
> }
>
> -static int watchdog_reboot_notifier(struct notifier_block *nb,
> - unsigned long code, void *data)
> -{
> - struct watchdog_device *wdd;
> -
> - wdd = container_of(nb, struct watchdog_device, reboot_nb);
> - if (code == SYS_DOWN || code == SYS_HALT) {
> - if (watchdog_active(wdd)) {
> - int ret;
> -
> - ret = wdd->ops->stop(wdd);
> - if (ret)
> - return NOTIFY_BAD;
> - }
> - }
> -
> - return NOTIFY_DONE;
> -}
> -
> /*
> * watchdog_dev_register: register a watchdog device
> * @wdd: watchdog device
> @@ -1134,22 +1114,8 @@ int watchdog_dev_register(struct watchdog_device *wdd)
> return ret;
>
> ret = watchdog_register_pretimeout(wdd);
> - if (ret) {
> + if (ret)
> watchdog_cdev_unregister(wdd);
> - return ret;
> - }
> -
> - if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status)) {
> - wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;
> -
> - ret = devm_register_reboot_notifier(&wdd->wd_data->dev,
> - &wdd->reboot_nb);
> - if (ret) {
> - pr_err("watchdog%d: Cannot register reboot notifier (%d)\n",
> - wdd->id, ret);
> - watchdog_dev_unregister(wdd);
> - }
> - }
>
> return ret;
> }
> --
> 2.20.1
>

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