[PATCH v2 2/3] Bluetooth: MGMT: protect hdev->mesh_pending with hdev->lock

[Baul Lee <baul.lee@xbow.com>]

hdev->mesh_pending carries the queued struct mgmt_mesh_tx of the mesh
mgmt interface.  It is extended and walked from syscall context under
hci_dev_lock(hdev), in mgmt_mesh_add() and mgmt_mesh_foreach(), and it
is unlinked and freed from the hci_cmd_sync worker under
hci_req_sync_lock(hdev), in send_cancel(), mesh_send_done_sync() and
mesh_next().  The two sides hold different mutexes, so the list has no
protection: MGMT_OP_MESH_READ_FEATURES on one socket can be mid-walk
while MGMT_OP_MESH_SEND_CANCEL on another frees the entry it is
standing on.

[   47.418949] BUG: KASAN: slab-use-after-free in send_count+0x4c/0x6c
[   47.419029] Read of size 1 at addr ffff000015943228 by task c2_race/191
[   47.419546]  send_count+0x4c/0x6c
[   47.419591]  mgmt_mesh_foreach+0x68/0x100
[   47.419637]  mesh_features+0x180/0x184
[   47.421345] Freed by task 59:
[   47.421555]  mgmt_mesh_remove+0x94/0x110
[   47.421589]  send_cancel+0xd8/0x1cc
[   47.421627]  hci_cmd_sync_work+0xac/0x128

Offset 40 of the freed 96-byte object is mesh_tx->handle, the byte
send_count() puts in the MESH_READ_FEATURES reply.  The walk also
follows the LIST_POISON1 left by the concurrent list_del(), which oopses
with hci_dev_lock held and never released, so every later mgmt command
on that controller blocks.

The same missing lock lets the worker free the object under mesh_send(),
which reads mesh_tx->handle into the command complete after queueing:

[   41.093914] BUG: KASAN: slab-use-after-free in mgmt_cmd_complete+0xd0/0x210
[   41.094353] Read of size 1 at addr ffff00000a0dea28 by task c1_poc/162
[   41.096944]  mgmt_mesh_remove+0x94/0x110
[   41.096975]  mesh_send_start_complete+0x128/0x160

That read already sits inside mesh_send()'s hci_dev_lock() section; it
is the worker side that is missing the lock.

Take hci_dev_lock(hdev) on the worker side, around the list work only
and not around hci_disable_advertising_sync(), and assert it in the
helpers that walk or extend the list.  hci_req_sync_lock -> hdev->lock
is the order this subsystem already uses: hci_cmd_sync_work() calls
entry->func under req_lock, and callbacks such as hci_update_eir_sync()
take hci_dev_lock() inside it.

mesh_next() and mesh_send_start_complete() are destroy callbacks, and
hci_cmd_sync_clear() runs a destroy callback under cmd_sync_work_lock,
which every mgmt caller of hci_cmd_sync_queue() takes with hdev->lock
already held.  Both therefore return before hci_dev_lock() when err is
-ECANCELED, as the other destroy callbacks in this file do.  Without
those returns lockdep reports a circular dependency, reached by closing
/dev/vhci while a mesh entry is queued behind a parked req_workqueue:

[   78.211873] ffff00001b0340b8 (&hdev->lock){+.+.}-{4:4}, at: mesh_send_start_complete+0x88/0xf4
               but task is already holding lock:
[   78.212596] ffff00001b0347c0 (&hdev->cmd_sync_work_lock){+.+.}-{4:4}, at: hci_cmd_sync_clear+0x60/0xd4
               -> #1 (&hdev->cmd_sync_work_lock){+.+.}-{4:4}:
[   78.214268]        hci_update_passive_scan+0x6c/0x84
[   78.214455]        mgmt_set_powered_complete+0x1b0/0x1f8

The other leg of the cycle, mgmt_set_powered_complete() calling
hci_update_passive_scan() with hdev->lock held, is an existing in-tree
path.  The entry such a return leaves on hdev->mesh_pending stays there,
as entries already do across an unregister.

Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Fixes: b338d91703fa ("Bluetooth: Implement support for Mesh")
Fixes: 3bb88524b7d0 ("Bluetooth: MGMT: iterate over mesh commands in mgmt_mesh_foreach()")
Cc: stable@vger.kernel.org
Signed-off-by: Baul Lee <baul.lee@xbow.com>
---
 net/bluetooth/mgmt.c      | 30 ++++++++++++++++++++++++++++--
 net/bluetooth/mgmt_util.c |  8 ++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
index 97408904f74b..853a80fd15af 100644
--- a/net/bluetooth/mgmt.c
+++ b/net/bluetooth/mgmt.c
@@ -1087,6 +1087,8 @@ static void mesh_send_complete(struct hci_dev *hdev,
 {
 	u8 handle = mesh_tx->handle;
 
+	lockdep_assert_held(&hdev->lock);
+
 	if (!silent)
 		mgmt_event(MGMT_EV_MESH_PACKET_CMPLT, hdev, &handle,
 			   sizeof(handle), NULL);
@@ -1101,11 +1103,16 @@ static int mesh_send_done_sync(struct hci_dev *hdev, void *data)
 	hci_dev_clear_flag(hdev, HCI_MESH_SENDING);
 	if (list_empty(&hdev->adv_instances))
 		hci_disable_advertising_sync(hdev);
+
+	hci_dev_lock(hdev);
+
 	mesh_tx = mgmt_mesh_next(hdev, NULL);
 
 	if (mesh_tx)
 		mesh_send_complete(hdev, mesh_tx, false);
 
+	hci_dev_unlock(hdev);
+
 	return 0;
 }
 
@@ -1113,11 +1120,19 @@ static int mesh_send_sync(struct hci_dev *hdev, void *data);
 static void mesh_send_start_complete(struct hci_dev *hdev, void *data, int err);
 static void mesh_next(struct hci_dev *hdev, void *data, int err)
 {
-	struct mgmt_mesh_tx *mesh_tx = mgmt_mesh_next(hdev, NULL);
+	struct mgmt_mesh_tx *mesh_tx;
 
-	if (!mesh_tx)
+	if (err == -ECANCELED)
 		return;
 
+	hci_dev_lock(hdev);
+
+	mesh_tx = mgmt_mesh_next(hdev, NULL);
+	if (!mesh_tx) {
+		hci_dev_unlock(hdev);
+		return;
+	}
+
 	err = hci_cmd_sync_queue(hdev, mesh_send_sync, mesh_tx,
 				 mesh_send_start_complete);
 
@@ -1125,6 +1140,8 @@ static void mesh_next(struct hci_dev *hdev, void *data, int err)
 		mesh_send_complete(hdev, mesh_tx, false);
 	else
 		hci_dev_set_flag(hdev, HCI_MESH_SENDING);
+
+	hci_dev_unlock(hdev);
 }
 
 static void mesh_send_done(struct work_struct *work)
@@ -2310,12 +2327,17 @@ static void mesh_send_start_complete(struct hci_dev *hdev, void *data, int err)
 	unsigned long mesh_send_interval;
 	u8 mgmt_err = mgmt_status(err);
 
+	if (err == -ECANCELED)
+		return;
+
 	/* Report any errors here, but don't report completion */
 
 	if (mgmt_err) {
 		hci_dev_clear_flag(hdev, HCI_MESH_SENDING);
 		/* Send Complete Error Code for handle */
+		hci_dev_lock(hdev);
 		mesh_send_complete(hdev, mesh_tx, false);
+		hci_dev_unlock(hdev);
 		return;
 	}
 
@@ -2421,6 +2443,8 @@ static int send_cancel(struct hci_dev *hdev, void *data)
 	struct mgmt_cp_mesh_send_cancel *cancel = (void *)cmd->param;
 	struct mgmt_mesh_tx *mesh_tx;
 
+	hci_dev_lock(hdev);
+
 	if (!cancel->handle) {
 		do {
 			mesh_tx = mgmt_mesh_next(hdev, cmd->sk);
@@ -2435,6 +2459,8 @@ static int send_cancel(struct hci_dev *hdev, void *data)
 			mesh_send_complete(hdev, mesh_tx, false);
 	}
 
+	hci_dev_unlock(hdev);
+
 	mgmt_cmd_complete(cmd->sk, hdev->id, MGMT_OP_MESH_SEND_CANCEL,
 			  0, NULL, 0);
 
diff --git a/net/bluetooth/mgmt_util.c b/net/bluetooth/mgmt_util.c
index 6ea107c0e054..a822091f2907 100644
--- a/net/bluetooth/mgmt_util.c
+++ b/net/bluetooth/mgmt_util.c
@@ -369,6 +369,8 @@ void mgmt_mesh_foreach(struct hci_dev *hdev,
 {
 	struct mgmt_mesh_tx *mesh_tx, *tmp;
 
+	lockdep_assert_held(&hdev->lock);
+
 	list_for_each_entry_safe(mesh_tx, tmp, &hdev->mesh_pending, list) {
 		if (!sk || mesh_tx->sk == sk)
 			cb(mesh_tx, data);
@@ -379,6 +381,8 @@ struct mgmt_mesh_tx *mgmt_mesh_next(struct hci_dev *hdev, struct sock *sk)
 {
 	struct mgmt_mesh_tx *mesh_tx;
 
+	lockdep_assert_held(&hdev->lock);
+
 	if (list_empty(&hdev->mesh_pending))
 		return NULL;
 
@@ -394,6 +398,8 @@ struct mgmt_mesh_tx *mgmt_mesh_find(struct hci_dev *hdev, u8 handle)
 {
 	struct mgmt_mesh_tx *mesh_tx;
 
+	lockdep_assert_held(&hdev->lock);
+
 	if (list_empty(&hdev->mesh_pending))
 		return NULL;
 
@@ -410,6 +416,8 @@ struct mgmt_mesh_tx *mgmt_mesh_add(struct sock *sk, struct hci_dev *hdev,
 {
 	struct mgmt_mesh_tx *mesh_tx;
 
+	lockdep_assert_held(&hdev->lock);
+
 	mesh_tx = kzalloc_obj(*mesh_tx);
 	if (!mesh_tx)
 		return NULL;
-- 
2.50.1 (Apple Git-155)