[PATCH v2] Bluetooth: mgmt: fix 'hdev->discovery.uuids' NULL dereference

[PATCH v2] Bluetooth: mgmt: fix 'hdev->discovery.uuids' NULL dereference

[Pavel Shpakovskiy]

'uuid_count' member of struct 'discovery_state' is assigned and read
without any locks, so there is a chance of situation when
uuid_count != 0, but uuids is NULL and there will be NULL pointer
dereference.

Possible race:
'hci_update_passive_scan_sync'
  'hci_discovery_filter_clear'
    hdev->discovery.uuid_count = 0;
      <----------------------preempted----------------------------->
                        'start_service_discovery'
                          // Set uuid_count to value != 0
                          hdev->discovery.uuid_count = uuid_count;
                          hdev->discovery.uuids = kmemdup(...);
      <----------------------preempted----------------------------->
    spin_lock(&hdev->discovery.lock);
    kfree(hdev->discovery.uuids);
    hdev->discovery.uuids = NULL;
    spin_unlock(&hdev->discovery.lock);

Now uuids == NULL and uuid_count != 0.
So 'mgmt_device_found' -> 'is_filter_match' -> 'eir_has_uuids' receives
non consistent discovery state, where NULL dereference of uuids happens.

To fix it let's add discovery.lock around every read/write of uuid_count,
uuids pair of struct members. It is also important to assign uuid_count
value only after success kmemdup() allocation in
start_service_discovery(), otherwise uuids is NULL, because kmemdup failed,
but uuid_count is already assigned to non zero value.

The following panic happens:

[ ] ------------[ cut here ]------------
[ ] Unable to handle kernel NULL pointer dereference at virtual
address 0000000000000000
[ ] Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
[ ] CPU: 0 PID: 15056 Comm: kworker/u9:2
[ ] Workqueue: hci0 hci_rx_work
[ ] pstate: 10400009 (nzcV daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ ] pc : eir_has_uuids+0x2d8/0x590
[ ] lr : is_filter_match+0x258/0x320
...
[ ] Call trace:
[ ]  eir_has_uuids+0x2d8/0x590
[ ]  is_filter_match+0x258/0x320
[ ]  mgmt_device_found+0x5b0/0xafc
[ ]  process_adv_report.part.0+0x8c8/0xf14
[ ]  hci_le_adv_report_evt+0x338/0x3f0
[ ]  hci_le_meta_evt+0x1f0/0x4c8
[ ]  hci_event_packet+0x440/0xc9c
[ ]  hci_rx_work+0x44c/0xaf8
[ ]  process_one_work+0x54c/0x103c
[ ]  worker_thread+0x6c4/0x10c4
[ ]  kthread+0x274/0x2ec
[ ]  ret_from_fork+0x10/0x20
[ ] Code: 14000004 91004021 eb14003f 54000180 (f9400024)
[ ] ---[ end trace 0000000000000000 ]---

Fixes: 2935e556850e ("Bluetooth: hci_sync: fix double free in 'hci_discovery_filter_clear()'")
Signed-off-by: Pavel Shpakovskiy <pashpakovskii@salutedevices.com>
---
 Changelog v1->v2:
 * Sleeping function was called from invalid context,
   need to allocate uuids before acquiring discovery.lock.

 include/net/bluetooth/hci_core.h |  2 +-
 net/bluetooth/mgmt.c             | 18 +++++++++++++-----
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index a7bffb908c1ec..f14239d1a817e 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -920,9 +920,9 @@ static inline void hci_discovery_filter_clear(struct hci_dev *hdev)
 	hdev->discovery.result_filtering = false;
 	hdev->discovery.report_invalid_rssi = true;
 	hdev->discovery.rssi = HCI_RSSI_INVALID;
-	hdev->discovery.uuid_count = 0;
 
 	spin_lock(&hdev->discovery.lock);
+	hdev->discovery.uuid_count = 0;
 	kfree(hdev->discovery.uuids);
 	hdev->discovery.uuids = NULL;
 	spin_unlock(&hdev->discovery.lock);
diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
index de5bd6b637b20..9917710f2ff56 100644
--- a/net/bluetooth/mgmt.c
+++ b/net/bluetooth/mgmt.c
@@ -6088,6 +6088,7 @@ static int start_service_discovery(struct sock *sk, struct hci_dev *hdev,
 	struct mgmt_pending_cmd *cmd;
 	const u16 max_uuid_count = ((U16_MAX - sizeof(*cp)) / 16);
 	u16 uuid_count, expected_len;
+	u8 (*uuids)[16] = NULL;
 	u8 status;
 	int err;
 
@@ -6164,12 +6165,10 @@ static int start_service_discovery(struct sock *sk, struct hci_dev *hdev,
 	hdev->discovery.result_filtering = true;
 	hdev->discovery.type = cp->type;
 	hdev->discovery.rssi = cp->rssi;
-	hdev->discovery.uuid_count = uuid_count;
 
 	if (uuid_count > 0) {
-		hdev->discovery.uuids = kmemdup(cp->uuids, uuid_count * 16,
-						GFP_KERNEL);
-		if (!hdev->discovery.uuids) {
+		uuids = kmemdup(cp->uuids, uuid_count * sizeof(*uuids), GFP_KERNEL);
+		if (!uuids) {
 			err = mgmt_cmd_complete(sk, hdev->id,
 						MGMT_OP_START_SERVICE_DISCOVERY,
 						MGMT_STATUS_FAILED,
@@ -6179,6 +6178,11 @@ static int start_service_discovery(struct sock *sk, struct hci_dev *hdev,
 		}
 	}
 
+	spin_lock(&hdev->discovery.lock);
+	hdev->discovery.uuids = uuids;
+	hdev->discovery.uuid_count = uuid_count;
+	spin_unlock(&hdev->discovery.lock);
+
 	err = hci_cmd_sync_queue(hdev, start_discovery_sync, cmd,
 				 start_discovery_complete);
 	if (err < 0) {
@@ -10243,6 +10247,7 @@ static bool is_filter_match(struct hci_dev *hdev, s8 rssi, u8 *eir,
 	     !hci_test_quirk(hdev, HCI_QUIRK_STRICT_DUPLICATE_FILTER))))
 		return  false;
 
+	spin_lock(&hdev->discovery.lock);
 	if (hdev->discovery.uuid_count != 0) {
 		/* If a list of UUIDs is provided in filter, results with no
 		 * matching UUID should be dropped.
@@ -10251,9 +10256,12 @@ static bool is_filter_match(struct hci_dev *hdev, s8 rssi, u8 *eir,
 				   hdev->discovery.uuids) &&
 		    !eir_has_uuids(scan_rsp, scan_rsp_len,
 				   hdev->discovery.uuid_count,
-				   hdev->discovery.uuids))
+				   hdev->discovery.uuids)) {
+			spin_unlock(&hdev->discovery.lock);
 			return false;
+		}
 	}
+	spin_unlock(&hdev->discovery.lock);
 
 	/* If duplicate filtering does not report RSSI changes, then restart
 	 * scanning to ensure updated result with updated RSSI values.
-- 
2.43.0

Re: [PATCH v2] Bluetooth: mgmt: fix 'hdev->discovery.uuids' NULL dereference

[patchwork-bot+bluetooth]

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Sat, 8 Aug 2026 19:31:11 +0300 you wrote:
> 'uuid_count' member of struct 'discovery_state' is assigned and read
> without any locks, so there is a chance of situation when
> uuid_count != 0, but uuids is NULL and there will be NULL pointer
> dereference.
> 
> Possible race:
> 'hci_update_passive_scan_sync'
>   'hci_discovery_filter_clear'
>     hdev->discovery.uuid_count = 0;
>       <----------------------preempted----------------------------->
>                         'start_service_discovery'
>                           // Set uuid_count to value != 0
>                           hdev->discovery.uuid_count = uuid_count;
>                           hdev->discovery.uuids = kmemdup(...);
>       <----------------------preempted----------------------------->
>     spin_lock(&hdev->discovery.lock);
>     kfree(hdev->discovery.uuids);
>     hdev->discovery.uuids = NULL;
>     spin_unlock(&hdev->discovery.lock);
> 
> [...]

Here is the summary with links:
  - [v2] Bluetooth: mgmt: fix 'hdev->discovery.uuids' NULL dereference
    https://git.kernel.org/bluetooth/bluetooth-next/c/99672791e9c9

You are awesome, thank you!
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