[PATCH v2] Bluetooth: MGMT: validate mesh send advertising payload length

[Keenan Dong <keenanat2000@gmail.com>]

mesh_send() currently bounds MGMT_OP_MESH_SEND by total command
length, but it never verifies that the bytes supplied for the
flexible adv_data[] array actually match the embedded adv_data_len
field. MGMT_MESH_SEND_SIZE only covers the fixed header, so a
truncated command can still pass the existing 20..50 byte range
check and later drive the async mesh send path past the end of the
queued command buffer.

Keep rejecting zero-length and oversized advertising payloads, but
validate adv_data_len explicitly and require the command length to
exactly match the flexible array size before queueing the request.

Fixes: b338d91703fa ("Bluetooth: Implement support for Mesh")
Reported-by: Keenan Dong <keenanat2000@gmail.com>
Signed-off-by: Keenan Dong <keenanat2000@gmail.com>
---
v2:
- replace the raw total-length range check in mesh_send()
- keep REJECTED for zero-length and oversized advertising payloads
- reject len/adv_data_len desynchronization with INVALID_PARAMS

Validation:
- vuln kernel reproduced the field-spanning write in
  hci_set_adv_instance_data() with a minimal direct-QEMU initramfs
  repro
- fixed kernel rejected malformed MGMT_OP_MESH_SEND requests at
  ingress in the same direct-QEMU setup

 net/bluetooth/mgmt.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
index e5f9287fb..18cee19aa 100644
--- a/net/bluetooth/mgmt.c
+++ b/net/bluetooth/mgmt.c
@@ -2478,6 +2478,7 @@ static int mesh_send(struct sock *sk, struct hci_dev *hdev, void *data, u16 len)
 	struct mgmt_mesh_tx *mesh_tx;
 	struct mgmt_cp_mesh_send *send = data;
 	struct mgmt_rp_mesh_read_features rp;
+	u16 expected_len;
 	bool sending;
 	int err = 0;
 
@@ -2485,12 +2486,19 @@ static int mesh_send(struct sock *sk, struct hci_dev *hdev, void *data, u16 len)
 	    !hci_dev_test_flag(hdev, HCI_MESH_EXPERIMENTAL))
 		return mgmt_cmd_status(sk, hdev->id, MGMT_OP_MESH_SEND,
 				       MGMT_STATUS_NOT_SUPPORTED);
-	if (!hci_dev_test_flag(hdev, HCI_LE_ENABLED) ||
-	    len <= MGMT_MESH_SEND_SIZE ||
-	    len > (MGMT_MESH_SEND_SIZE + 31))
+	if (!hci_dev_test_flag(hdev, HCI_LE_ENABLED))
+		return mgmt_cmd_status(sk, hdev->id, MGMT_OP_MESH_SEND,
+				       MGMT_STATUS_REJECTED);
+
+	if (!send->adv_data_len || send->adv_data_len > 31)
 		return mgmt_cmd_status(sk, hdev->id, MGMT_OP_MESH_SEND,
 				       MGMT_STATUS_REJECTED);
 
+	expected_len = struct_size(send, adv_data, send->adv_data_len);
+	if (expected_len != len)
+		return mgmt_cmd_status(sk, hdev->id, MGMT_OP_MESH_SEND,
+				       MGMT_STATUS_INVALID_PARAMS);
+
 	hci_dev_lock(hdev);
 
 	memset(&rp, 0, sizeof(rp));
-- 
2.43.0