Hi Bernie,
On Tue, Sep 28, 2021 at 4:01 PM Bernie Conrad <bernie@xxxxxxxxxxxxxxxxx> wrote:
>
> There is a current use after free possible on a gatt server if a client
> disconnects while a WriteValue call is being processed with dbus.
>
> This patch includes the addition of a pending disconnect callback to handle
> cleanup better if a disconnect occurs during a write, an acquire write
> or read operation using bt_att_register_disconnect with the cb.
>
> v2: Fixed a bad call to pending_read_new
>
> ---
> src/gatt-database.c | 115 +++++++++++++++++++++++++-------------------
> 1 file changed, 65 insertions(+), 50 deletions(-)
>
> diff --git a/src/gatt-database.c b/src/gatt-database.c
> index 1f7ce5f02..a03c579cf 100644
> --- a/src/gatt-database.c
> +++ b/src/gatt-database.c
> @@ -933,6 +933,24 @@ static struct btd_device *att_get_device(struct bt_att *att)
> return btd_adapter_find_device(adapter, &dst, dst_type);
> }
>
> +
> +static void pending_op_free(void *data)
> +{
> + struct pending_op *op = data;
> +
> + if (op->owner_queue)
> + queue_remove(op->owner_queue, op);
> +
> + free(op);
We might need to do something like the following:
https://gist.github.com/Vudentz/958d540591d1ae6a32d226ef8a0d6d54
Otherwise we risk the op being freeing when the op is completely
properly but when att is disconnected it still runs
pending_disconnect_cb causing a UAF.
> +}
> +
> +static void pending_disconnect_cb(int err, void *user_data)
> +{
> + struct pending_op *op = user_data;
> +
> + op->owner_queue = NULL;
> +}
> +
> static struct pending_op *pending_ccc_new(struct bt_att *att,
> struct gatt_db_attribute *attrib,
> uint16_t value,
> @@ -956,17 +974,12 @@ static struct pending_op *pending_ccc_new(struct bt_att *att,
> op->attrib = attrib;
> op->link_type = link_type;
>
> - return op;
> -}
> + bt_att_register_disconnect(att,
> + pending_disconnect_cb,
> + op,
> + NULL);
>
> -static void pending_op_free(void *data)
> -{
> - struct pending_op *op = data;
> -
> - if (op->owner_queue)
> - queue_remove(op->owner_queue, op);
> -
> - free(op);
> + return op;
> }
>
> static void gatt_ccc_write_cb(struct gatt_db_attribute *attrib,
> @@ -2169,24 +2182,26 @@ done:
> gatt_db_attribute_read_result(op->attrib, op->id, ecode, value, len);
> }
>
> -static struct pending_op *pending_read_new(struct btd_device *device,
> +
> +static struct pending_op *pending_read_new(struct bt_att *att,
> struct queue *owner_queue,
> struct gatt_db_attribute *attrib,
> - unsigned int id, uint16_t offset,
> - uint8_t link_type)
> + unsigned int id, uint16_t offset)
> {
> struct pending_op *op;
>
> op = new0(struct pending_op, 1);
>
> op->owner_queue = owner_queue;
> - op->device = device;
> + op->device = att_get_device(att);
> op->attrib = attrib;
> op->id = id;
> op->offset = offset;
> - op->link_type = link_type;
> + op->link_type = bt_att_get_link_type(att);
> queue_push_tail(owner_queue, op);
>
> + bt_att_register_disconnect(att, pending_disconnect_cb, op, NULL);
> +
> return op;
> }
>
> @@ -2243,18 +2258,16 @@ static void read_setup_cb(DBusMessageIter *iter, void *user_data)
> dbus_message_iter_close_container(iter, &dict);
> }
>
> -static struct pending_op *send_read(struct btd_device *device,
> +static struct pending_op *send_read(struct bt_att *att,
> struct gatt_db_attribute *attrib,
> GDBusProxy *proxy,
> struct queue *owner_queue,
> unsigned int id,
> - uint16_t offset,
> - uint8_t link_type)
> + uint16_t offset)
> {
> struct pending_op *op;
>
> - op = pending_read_new(device, owner_queue, attrib, id, offset,
> - link_type);
> + op = pending_read_new(att, owner_queue, attrib, id, offset);
>
> if (g_dbus_proxy_method_call(proxy, "ReadValue", read_setup_cb,
> read_reply_cb, op, pending_op_free) == TRUE)
> @@ -2337,15 +2350,17 @@ static void write_reply_cb(DBusMessage *message, void *user_data)
> }
>
> done:
> - gatt_db_attribute_write_result(op->attrib, op->id, ecode);
> + // Make sure that only reply if the device is connected
> + if (btd_device_is_connected(op->device))
> + gatt_db_attribute_write_result(op->attrib, op->id, ecode);
> }
>
> -static struct pending_op *pending_write_new(struct btd_device *device,
> +static struct pending_op *pending_write_new(struct bt_att *att,
> struct queue *owner_queue,
> struct gatt_db_attribute *attrib,
> unsigned int id,
> const uint8_t *value, size_t len,
> - uint16_t offset, uint8_t link_type,
> + uint16_t offset,
> bool is_characteristic,
> bool prep_authorize)
> {
> @@ -2356,33 +2371,37 @@ static struct pending_op *pending_write_new(struct btd_device *device,
> op->data.iov_base = (uint8_t *) value;
> op->data.iov_len = len;
>
> - op->device = device;
> + op->device = att_get_device(att);
> op->owner_queue = owner_queue;
> op->attrib = attrib;
> op->id = id;
> op->offset = offset;
> - op->link_type = link_type;
> + op->link_type = bt_att_get_link_type(att);
> op->is_characteristic = is_characteristic;
> op->prep_authorize = prep_authorize;
> queue_push_tail(owner_queue, op);
>
> + bt_att_register_disconnect(att,
> + pending_disconnect_cb,
> + op, NULL);
> +
> return op;
> }
>
> -static struct pending_op *send_write(struct btd_device *device,
> +static struct pending_op *send_write(struct bt_att *att,
> struct gatt_db_attribute *attrib,
> GDBusProxy *proxy,
> struct queue *owner_queue,
> unsigned int id,
> const uint8_t *value, size_t len,
> - uint16_t offset, uint8_t link_type,
> + uint16_t offset,
> bool is_characteristic,
> bool prep_authorize)
> {
> struct pending_op *op;
>
> - op = pending_write_new(device, owner_queue, attrib, id, value, len,
> - offset, link_type, is_characteristic,
> + op = pending_write_new(att, owner_queue, attrib, id, value, len,
> + offset, is_characteristic,
> prep_authorize);
>
> if (g_dbus_proxy_method_call(proxy, "WriteValue", write_setup_cb,
> @@ -2558,17 +2577,16 @@ static void acquire_write_setup(DBusMessageIter *iter, void *user_data)
> }
>
> static struct pending_op *acquire_write(struct external_chrc *chrc,
> - struct btd_device *device,
> + struct bt_att *att,
> struct gatt_db_attribute *attrib,
> unsigned int id,
> - const uint8_t *value, size_t len,
> - uint8_t link_type)
> + const uint8_t *value, size_t len)
> {
> struct pending_op *op;
> bool acquiring = !queue_isempty(chrc->pending_writes);
>
> - op = pending_write_new(device, chrc->pending_writes, attrib, id, value,
> - len, 0, link_type, false, false);
> + op = pending_write_new(att, chrc->pending_writes, attrib, id, value,
> + len, 0, false, false);
>
> if (acquiring)
> return op;
> @@ -2851,8 +2869,8 @@ static void desc_read_cb(struct gatt_db_attribute *attrib,
> goto fail;
> }
>
> - if (send_read(device, attrib, desc->proxy, desc->pending_reads, id,
> - offset, bt_att_get_link_type(att)))
> + if (send_read(att, attrib, desc->proxy, desc->pending_reads, id,
> + offset))
> return;
>
> fail:
> @@ -2883,10 +2901,9 @@ static void desc_write_cb(struct gatt_db_attribute *attrib,
> if (opcode == BT_ATT_OP_PREP_WRITE_REQ) {
> if (!device_is_trusted(device) && !desc->prep_authorized &&
> desc->req_prep_authorization)
> - send_write(device, attrib, desc->proxy,
> + send_write(att, attrib, desc->proxy,
> desc->pending_writes, id, value, len,
> - offset, bt_att_get_link_type(att),
> - false, true);
> + offset, false, true);
> else
> gatt_db_attribute_write_result(attrib, id, 0);
>
> @@ -2896,9 +2913,8 @@ static void desc_write_cb(struct gatt_db_attribute *attrib,
> if (opcode == BT_ATT_OP_EXEC_WRITE_REQ)
> desc->prep_authorized = false;
>
> - if (send_write(device, attrib, desc->proxy, desc->pending_writes, id,
> - value, len, offset, bt_att_get_link_type(att), false,
> - false))
> + if (send_write(att, attrib, desc->proxy, desc->pending_writes, id,
> + value, len, offset, false, false))
> return;
>
> fail:
> @@ -2977,8 +2993,8 @@ static void chrc_read_cb(struct gatt_db_attribute *attrib,
> goto fail;
> }
>
> - if (send_read(device, attrib, chrc->proxy, chrc->pending_reads, id,
> - offset, bt_att_get_link_type(att)))
> + if (send_read(att, attrib, chrc->proxy, chrc->pending_reads, id,
> + offset))
> return;
>
> fail:
> @@ -3016,9 +3032,9 @@ static void chrc_write_cb(struct gatt_db_attribute *attrib,
> if (opcode == BT_ATT_OP_PREP_WRITE_REQ) {
> if (!device_is_trusted(device) && !chrc->prep_authorized &&
> chrc->req_prep_authorization)
> - send_write(device, attrib, chrc->proxy, queue,
> + send_write(att, attrib, chrc->proxy, queue,
> id, value, len, offset,
> - bt_att_get_link_type(att), true, true);
> + true, true);
> else
> gatt_db_attribute_write_result(attrib, id, 0);
>
> @@ -3039,13 +3055,12 @@ static void chrc_write_cb(struct gatt_db_attribute *attrib,
> }
>
> if (g_dbus_proxy_get_property(chrc->proxy, "WriteAcquired", &iter)) {
> - if (acquire_write(chrc, device, attrib, id, value, len,
> - bt_att_get_link_type(att)))
> + if (acquire_write(chrc, att, attrib, id, value, len))
> return;
> }
>
> - if (send_write(device, attrib, chrc->proxy, queue, id, value, len,
> - offset, bt_att_get_link_type(att), false, false))
> + if (send_write(att, attrib, chrc->proxy, queue, id, value, len,
> + offset, false, false))
> return;
>
> fail:
> --
> 2.17.1
>
--
Luiz Augusto von Dentz
