Bluetooth: MGMT: validate Add Extended Advertising Data length

Bluetooth: MGMT: validate Add Extended Advertising Data length

MGMT_OP_ADD_EXT_ADV_DATA is registered as a variable-length command,
with MGMT_ADD_EXT_ADV_DATA_SIZE as the fixed header size.  The handler
then uses cp->adv_data_len and cp->scan_rsp_len to validate and copy
cp->data, but it never checks that those bytes are part of the mgmt
command payload.

A short command can therefore make add_ext_adv_data() pass an
out-of-bounds pointer into tlv_data_is_valid().  If the bytes beyond
the command buffer are addressable, they can also be copied into the
advertising instance as scan response data, where the caller can read
them back via MGMT_OP_GET_ADV_INSTANCE.  The trigger requires
CAP_NET_ADMIN in the initial user namespace; KASAN reports an 8-byte
slab-out-of-bounds read.

Reject commands whose length does not match the fixed header plus both
advertising data lengths before parsing cp->data.

Fixes: 12410572833a ("Bluetooth: Break add adv into two mgmt commands")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>