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Subject[PATCH] watchdog: fix UAF in reboot notifier handling in watchdog core code
Date
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>
---
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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