[PATCH 7.2 81/82] Bluetooth: MGMT: reject HCI_CMD_SYNC params_len above 255

7.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ali Ahmet Memis <[email protected]>

commit 5d95286b6d6e8f1d304da7522bfa6860fc017e48 upstream.

mgmt_hci_cmd_sync() checks that the message length agrees with params_len
but puts no upper bound on it. params_len is __le16 while the parameter
length in the HCI command header is a u8:

	struct hci_command_hdr {
		__le16	opcode;
		__u8	plen;
	} __packed;

hci_cmd_sync_alloc() assigns one to the other:

	hdr->plen = plen;

	if (plen)
		skb_put_data(skb, param, plen);

so a params_len of 256 leaves plen at 0 while all 256 bytes are still
appended. The frame handed to the driver then declares no parameters and
carries 256 of them. On a length framed transport such as H:4 the
controller takes the trailing bytes as the start of the next packet.

The mgmt socket MTU is HCI_MAX_FRAME_SIZE, so params_len can reach about
1KB this way. Commit 03f1700b9b4d ("Bluetooth: MGMT: reject malformed
HCI_CMD_SYNC commands") only made params_len agree with the message
length, a value that fits the message but not the header field is still
accepted.

Reject params_len that does not fit the header field.

Fixes: 827af4787e74 ("Bluetooth: MGMT: Add initial implementation of MGMT_OP_HCI_CMD_SYNC")
Cc: [email protected]
Signed-off-by: Ali Ahmet Memis <[email protected]>
Signed-off-by: Luiz Augusto von Dentz <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 net/bluetooth/mgmt.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/net/bluetooth/mgmt.c
+++ b/net/bluetooth/mgmt.c
@@ -2668,6 +2668,14 @@ static int mgmt_hci_cmd_sync(struct sock
 		return mgmt_cmd_status(sk, hdev->id, MGMT_OP_HCI_CMD_SYNC,
 				       MGMT_STATUS_INVALID_PARAMS);
 
+	/* The HCI command header carries the parameter length in a u8, a
+	 * larger value would be truncated there while the parameters are
+	 * still appended to the frame in full.
+	 */
+	if (le16_to_cpu(cp->params_len) > U8_MAX)
+		return mgmt_cmd_status(sk, hdev->id, MGMT_OP_HCI_CMD_SYNC,
+				       MGMT_STATUS_INVALID_PARAMS);
+
 	hci_dev_lock(hdev);
 	cmd = mgmt_pending_new(sk, MGMT_OP_HCI_CMD_SYNC, hdev, data, len);
 	if (!cmd)