[PATCH] Bluetooth: msft: fix slab-use-after-free in msft_do_close()

[PATCH] Bluetooth: msft: fix slab-use-after-free in msft_do_close()

[Sungwoo Kim]

Add refcnt to safely destroy hdev->msft_data.

How msft is used after freed:

[use]
msft_do_close()
  if (!msft)                      ...(1)
    return;
  mutex_lock(&msft->filter_lock); ...(4) <- used after freed

[free]
msft_unregister()
  hdev->msft_data = NULL;         ...(2)
  kfree(msft);                    ...(3) <- msft is freed

==================================================================
BUG: KASAN: slab-use-after-free in __mutex_lock_common kernel/locking/mutex.c:587 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock+0x8f/0xc30 kernel/locking/mutex.c:752
Read of size 8 at addr ffff888106cbbca8 by task kworker/u5:2/309

CPU: 0 PID: 309 Comm: kworker/u5:2 Not tainted 6.9.0-rc5+ #5
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Workqueue: hci4 hci_error_reset
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x140 lib/dump_stack.c:114
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x191/0x560 mm/kasan/report.c:488
 kasan_report+0xe2/0x120 mm/kasan/report.c:601
 __asan_report_load8_noabort+0x18/0x20 mm/kasan/report_generic.c:381
 __mutex_lock_common kernel/locking/mutex.c:587 [inline]
 __mutex_lock+0x8f/0xc30 kernel/locking/mutex.c:752
 mutex_lock_nested+0x1f/0x30 kernel/locking/mutex.c:804
 msft_do_close+0x292/0x700 net/bluetooth/msft.c:694
 hci_dev_close_sync+0x906/0xf10 net/bluetooth/hci_sync.c:5168
 hci_dev_do_close net/bluetooth/hci_core.c:554 [inline]
 hci_error_reset+0x152/0x410 net/bluetooth/hci_core.c:1091
 process_one_work kernel/workqueue.c:3254 [inline]
 process_scheduled_works+0x90f/0x1530 kernel/workqueue.c:3335
 worker_thread+0x926/0xe70 kernel/workqueue.c:3416
 kthread+0x2e3/0x380 kernel/kthread.c:388
 ret_from_fork+0x5c/0x90 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

Allocated by task 7328:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x30/0x70 mm/kasan/common.c:68
 kasan_save_alloc_info+0x3c/0x50 mm/kasan/generic.c:565
 poison_kmalloc_redzone mm/kasan/common.c:370 [inline]
 __kasan_kmalloc+0xa2/0xc0 mm/kasan/common.c:387
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 kmalloc_trace+0x20c/0x3e0 mm/slub.c:3997
 kmalloc include/linux/slab.h:628 [inline]
 kzalloc include/linux/slab.h:749 [inline]
 msft_register+0x66/0x1d0 net/bluetooth/msft.c:760
 hci_register_dev+0x85e/0x9a0 net/bluetooth/hci_core.c:2737
 __vhci_create_device drivers/bluetooth/hci_vhci.c:438 [inline]
 vhci_create_device+0x390/0x720 drivers/bluetooth/hci_vhci.c:480
 vhci_get_user drivers/bluetooth/hci_vhci.c:537 [inline]
 vhci_write+0x39b/0x460 drivers/bluetooth/hci_vhci.c:617
 call_write_iter include/linux/fs.h:2110 [inline]
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0x8eb/0xb50 fs/read_write.c:590
 ksys_write+0x106/0x1f0 fs/read_write.c:643
 __do_sys_write fs/read_write.c:655 [inline]
 __se_sys_write fs/read_write.c:652 [inline]
 __x64_sys_write+0x84/0xa0 fs/read_write.c:652
 x64_sys_call+0x271a/0x2ce0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x9c/0x130 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Freed by task 7332:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x30/0x70 mm/kasan/common.c:68
 kasan_save_free_info+0x44/0x50 mm/kasan/generic.c:579
 poison_slab_object+0x11a/0x190 mm/kasan/common.c:240
 __kasan_slab_free+0x3b/0x60 mm/kasan/common.c:256
 kasan_slab_free include/linux/kasan.h:184 [inline]
 slab_free_hook mm/slub.c:2106 [inline]
 slab_free mm/slub.c:4280 [inline]
 kfree+0x13c/0x330 mm/slub.c:4390
 msft_unregister+0x9d/0x120 net/bluetooth/msft.c:785
 hci_unregister_dev+0x1d9/0x520 net/bluetooth/hci_core.c:2771
 vhci_release+0x8c/0xe0 drivers/bluetooth/hci_vhci.c:674
 __fput+0x36f/0x750 fs/file_table.c:422
 ____fput+0x1e/0x30 fs/file_table.c:450
 task_work_run+0x1da/0x280 kernel/task_work.c:180
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0x856/0x2210 kernel/exit.c:878
 do_group_exit+0x201/0x2c0 kernel/exit.c:1027
 get_signal+0x12ff/0x1380 kernel/signal.c:2911
 arch_do_signal_or_restart+0x3b/0x650 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0xcc/0x2a0 kernel/entry/common.c:218
 do_syscall_64+0xa8/0x130 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

The buggy address belongs to the object at ffff888106cbbc00
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 168 bytes inside of
 freed 256-byte region [ffff888106cbbc00, ffff888106cbbd00)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x106cba
head: order:1 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x17ffffe0000840(slab|head|node=0|zone=2|lastcpupid=0x3fffff)
page_type: 0xffffffff()
raw: 0017ffffe0000840 ffff888100042040 ffffea00042de590 ffffea00041b3e10
raw: 0000000000000000 00000000000a000a 00000001ffffffff 0000000000000000
head: 0017ffffe0000840 ffff888100042040 ffffea00042de590 ffffea00041b3e10
head: 0000000000000000 00000000000a000a 00000001ffffffff 0000000000000000
head: 0017ffffe0000001 ffffea00041b2e81 dead000000000122 00000000ffffffff
head: 0000000200000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888106cbbb80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888106cbbc00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888106cbbc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff888106cbbd00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888106cbbd80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Fixes: 9e14606d8f38 ("Bluetooth: disable advertisement filters during suspend")
Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
---
 net/bluetooth/msft.c | 124 ++++++++++++++++++++++++++++++++++---------
 1 file changed, 99 insertions(+), 25 deletions(-)

diff --git a/net/bluetooth/msft.c b/net/bluetooth/msft.c
index 9612c5d1b..d42150cf9 100644
--- a/net/bluetooth/msft.c
+++ b/net/bluetooth/msft.c
@@ -132,10 +132,45 @@ struct msft_data {
 	__u8 filter_enabled;
 	/* To synchronize add/remove address filter and monitor device event.*/
 	struct mutex filter_lock;
+	struct kref	kref;
 };
 
+static void msft_data_free(struct kref *kref);
+
+static struct msft_data *msft_data_hold_unless_zero(struct msft_data *msft)
+{
+	BT_DBG("msft %p orig refcnt %u", msft, kref_read(&msft->kref));
+
+	if (!msft)
+		return NULL;
+
+	if (!kref_get_unless_zero(&msft->kref))
+		return NULL;
+
+	return msft;
+}
+
+static void msft_data_put(struct msft_data *msft)
+{
+	BT_DBG("msft %p orig refcnt %u", msft, kref_read(&msft->kref));
+
+	kref_put(&msft->kref, msft_data_free);
+}
+
+static void msft_data_free(struct kref *kref)
+{
+	struct msft_data *msft = container_of(kref, struct msft_data, kref);
+
+	BT_DBG("msft %p", msft);
+
+	kfree(msft->evt_prefix);
+	mutex_destroy(&msft->filter_lock);
+	kfree(msft);
+}
+
 bool msft_monitor_supported(struct hci_dev *hdev)
 {
+	/* msft_get_features() holds and put hdev->msft_data */
 	return !!(msft_get_features(hdev) & MSFT_FEATURE_MASK_LE_ADV_MONITOR);
 }
 
@@ -449,12 +484,17 @@ static int msft_remove_monitor_sync(struct hci_dev *hdev,
 /* This function requires the caller holds hci_req_sync_lock */
 int msft_suspend_sync(struct hci_dev *hdev)
 {
-	struct msft_data *msft = hdev->msft_data;
+	struct msft_data *msft;
 	struct adv_monitor *monitor;
 	int handle = 0;
 
-	if (!msft || !msft_monitor_supported(hdev))
+	msft = msft_data_hold_unless_zero(hdev->msft_data);
+	if (!msft)
 		return 0;
+	if (!msft_monitor_supported(hdev)) {
+		msft_data_put(msft);
+		return 0;
+	}
 
 	msft->suspending = true;
 
@@ -471,6 +511,7 @@ int msft_suspend_sync(struct hci_dev *hdev)
 	/* All monitors have been removed */
 	msft->suspending = false;
 
+	msft_data_put(msft);
 	return 0;
 }
 
@@ -608,11 +649,17 @@ static void reregister_monitor(struct hci_dev *hdev)
 /* This function requires the caller holds hci_req_sync_lock */
 int msft_resume_sync(struct hci_dev *hdev)
 {
-	struct msft_data *msft = hdev->msft_data;
+	struct msft_data *msft;
 
-	if (!msft || !msft_monitor_supported(hdev))
+	msft = msft_data_hold_unless_zero(hdev->msft_data);
+	if (!msft)
 		return 0;
 
+	if (!msft_monitor_supported(hdev)) {
+		msft_data_put(msft);
+		return 0;
+	}
+
 	hci_dev_lock(hdev);
 
 	/* Clear already tracked devices on resume. Once the monitors are
@@ -625,17 +672,19 @@ int msft_resume_sync(struct hci_dev *hdev)
 
 	reregister_monitor(hdev);
 
+	msft_data_put(msft);
 	return 0;
 }
 
 /* This function requires the caller holds hci_req_sync_lock */
 void msft_do_open(struct hci_dev *hdev)
 {
-	struct msft_data *msft = hdev->msft_data;
+	struct msft_data *msft;
 
 	if (hdev->msft_opcode == HCI_OP_NOP)
 		return;
 
+	msft = msft_data_hold_unless_zero(hdev->msft_data);
 	if (!msft) {
 		bt_dev_err(hdev, "MSFT extension not registered");
 		return;
@@ -650,8 +699,7 @@ void msft_do_open(struct hci_dev *hdev)
 	msft->features = 0;
 
 	if (!read_supported_features(hdev, msft)) {
-		hdev->msft_data = NULL;
-		kfree(msft);
+		msft_data_put(msft);
 		return;
 	}
 
@@ -663,15 +711,17 @@ void msft_do_open(struct hci_dev *hdev)
 		 */
 		reregister_monitor(hdev);
 	}
+	msft_data_put(msft);
 }
 
 void msft_do_close(struct hci_dev *hdev)
 {
-	struct msft_data *msft = hdev->msft_data;
+	struct msft_data *msft;
 	struct msft_monitor_advertisement_handle_data *handle_data, *tmp;
 	struct msft_monitor_addr_filter_data *address_filter, *n;
 	struct adv_monitor *monitor;
 
+	msft = msft_data_hold_unless_zero(hdev->msft_data);
 	if (!msft)
 		return;
 
@@ -705,6 +755,8 @@ void msft_do_close(struct hci_dev *hdev)
 	hdev->advmon_pend_notify = false;
 	msft_monitor_device_del(hdev, 0, NULL, 0, true);
 
+	msft_data_put(msft);
+
 	hci_dev_unlock(hdev);
 }
 
@@ -767,6 +819,7 @@ void msft_register(struct hci_dev *hdev)
 	INIT_LIST_HEAD(&msft->address_filters);
 	hdev->msft_data = msft;
 	mutex_init(&msft->filter_lock);
+	kref_init(&msft->kref);
 }
 
 void msft_unregister(struct hci_dev *hdev)
@@ -779,10 +832,7 @@ void msft_unregister(struct hci_dev *hdev)
 	bt_dev_dbg(hdev, "Unregister MSFT extension");
 
 	hdev->msft_data = NULL;
-
-	kfree(msft->evt_prefix);
-	mutex_destroy(&msft->filter_lock);
-	kfree(msft);
+	msft_data_put(msft);
 }
 
 /* This function requires the caller holds hdev->lock */
@@ -1068,10 +1118,11 @@ static void msft_monitor_device_evt(struct hci_dev *hdev, struct sk_buff *skb)
 
 void msft_vendor_evt(struct hci_dev *hdev, void *data, struct sk_buff *skb)
 {
-	struct msft_data *msft = hdev->msft_data;
+	struct msft_data *msft;
 	u8 *evt_prefix;
 	u8 *evt;
 
+	msft = msft_data_hold_unless_zero(hdev->msft_data);
 	if (!msft)
 		return;
 
@@ -1081,21 +1132,21 @@ void msft_vendor_evt(struct hci_dev *hdev, void *data, struct sk_buff *skb)
 	if (msft->evt_prefix_len > 0) {
 		evt_prefix = msft_skb_pull(hdev, skb, 0, msft->evt_prefix_len);
 		if (!evt_prefix)
-			return;
+			goto done;
 
 		if (memcmp(evt_prefix, msft->evt_prefix, msft->evt_prefix_len))
-			return;
+			goto done;
 	}
 
 	/* Every event starts at least with an event code and the rest of
 	 * the data is variable and depends on the event code.
 	 */
 	if (skb->len < 1)
-		return;
+		goto done;
 
 	evt = msft_skb_pull(hdev, skb, 0, sizeof(*evt));
 	if (!evt)
-		return;
+		goto done;
 
 	hci_dev_lock(hdev);
 
@@ -1112,13 +1163,24 @@ void msft_vendor_evt(struct hci_dev *hdev, void *data, struct sk_buff *skb)
 	}
 
 	hci_dev_unlock(hdev);
+
+done:
+	msft_data_put(msft);
 }
 
 __u64 msft_get_features(struct hci_dev *hdev)
 {
-	struct msft_data *msft = hdev->msft_data;
+	struct msft_data *msft;
+	unsigned long long features;
+
+	msft = msft_data_hold_unless_zero(hdev->msft_data);
+	if (!msft)
+		return 0;
+
+	features = msft->features;
 
-	return msft ? msft->features : 0;
+	msft_data_put(msft);
+	return features;
 }
 
 static void msft_le_set_advertisement_filter_enable_cb(struct hci_dev *hdev,
@@ -1152,37 +1214,48 @@ static void msft_le_set_advertisement_filter_enable_cb(struct hci_dev *hdev,
 /* This function requires the caller holds hci_req_sync_lock */
 int msft_add_monitor_pattern(struct hci_dev *hdev, struct adv_monitor *monitor)
 {
-	struct msft_data *msft = hdev->msft_data;
+	struct msft_data *msft;
+	int err;
 
+	msft = msft_data_hold_unless_zero(hdev->msft_data);
 	if (!msft)
 		return -EOPNOTSUPP;
 
-	if (msft->resuming || msft->suspending)
+	if (msft->resuming || msft->suspending) {
+		msft_data_put(msft);
 		return -EBUSY;
+	}
 
-	return msft_add_monitor_sync(hdev, monitor);
+	err = msft_add_monitor_sync(hdev, monitor);
+	msft_data_put(msft);
+	return err;
 }
 
 /* This function requires the caller holds hci_req_sync_lock */
 int msft_remove_monitor(struct hci_dev *hdev, struct adv_monitor *monitor)
 {
-	struct msft_data *msft = hdev->msft_data;
+	struct msft_data *msft;
+	int err;
 
+	msft = msft_data_hold_unless_zero(hdev->msft_data);
 	if (!msft)
 		return -EOPNOTSUPP;
 
 	if (msft->resuming || msft->suspending)
 		return -EBUSY;
 
-	return msft_remove_monitor_sync(hdev, monitor);
+	err = msft_remove_monitor_sync(hdev, monitor);
+	msft_data_put(msft);
+	return err;
 }
 
 int msft_set_filter_enable(struct hci_dev *hdev, bool enable)
 {
 	struct msft_cp_le_set_advertisement_filter_enable cp;
-	struct msft_data *msft = hdev->msft_data;
+	struct msft_data *msft;
 	int err;
 
+	msft = msft_data_hold_unless_zero(hdev->msft_data);
 	if (!msft)
 		return -EOPNOTSUPP;
 
@@ -1193,6 +1266,7 @@ int msft_set_filter_enable(struct hci_dev *hdev, bool enable)
 
 	msft_le_set_advertisement_filter_enable_cb(hdev, &cp, err);
 
+	msft_data_put(msft);
 	return 0;
 }
 
-- 
2.34.1

Re: [PATCH] Bluetooth: msft: fix slab-use-after-free in msft_do_close()

[Sungwoo Kim]

Hello,

Could you not apply this? I found an error.

On Sat, Apr 27, 2024 at 1:19 AM Sungwoo Kim <iam@sung-woo.kim> wrote:
>
> +
> +static struct msft_data *msft_data_hold_unless_zero(struct msft_data *msft)
> +{
> +       BT_DBG("msft %p orig refcnt %u", msft, kref_read(&msft->kref));

Here, msft could be NULL. &msft->kref causes a null-ptr-deref error.
I already sent a v2 patch fixing this.

> +
> +       if (!msft)
> +               return NULL;
> +
> +       if (!kref_get_unless_zero(&msft->kref))
> +               return NULL;
> +
> +       return msft;
> +}
> +

Thanks,
Sungwoo.