Re: out-of-bounds access in sound/soc/sof/topology.c

Pierre-Louis Bossart
2022-04-19T13:08:10Z

On 4/19/22 06:50, Péter Ujfalusi wrote:
> Hi Sergey, Pierre,
>
> On 15/04/2022 19:00, Pierre-Louis Bossart wrote:
>> Thanks Sergey for this email.
>>
>> On 4/15/22 04:23, Sergey Senozhatsky wrote:
>>> Hi,
>>>
>>> I'm running 5.10.111 LTS, so if this has been fixed already then we definitely
>>> want to cherry pick the fix for -stable.
>
> I'm afraid, that this is still valid as of today, but in real life I
> don't think it can happen.
>
>>> Anonymous union in this struct is of zero size
>>>
>>> /* generic control data */
>>> struct sof_ipc_ctrl_data {
>>> struct sof_ipc_reply rhdr;
>>> uint32_t comp_id;
>>>
>>> /* control access and data type */
>>> uint32_t type; /**< enum sof_ipc_ctrl_type */
>>> uint32_t cmd; /**< enum sof_ipc_ctrl_cmd */
>>> uint32_t index; /**< control index for comps > 1 control */
>>>
>>> /* control data - can either be appended or DMAed from host */
>>> struct sof_ipc_host_buffer buffer;
>>> uint32_t num_elems; /**< in array elems or bytes for data type */
>>> uint32_t elems_remaining; /**< elems remaining if sent in parts */
>>>
>>> uint32_t msg_index; /**< for large messages sent in parts */
>>>
>>> /* reserved for future use */
>>> uint32_t reserved[6];
>>>
>>> /* control data - add new types if needed */
>>> union {
>>> /* channel values can be used by volume type controls */
>>> struct sof_ipc_ctrl_value_chan chanv[0];
>>> /* component values used by routing controls like mux, mixer */
>>> struct sof_ipc_ctrl_value_comp compv[0];
>>> /* data can be used by binary controls */
>>> struct sof_abi_hdr data[0];
>>> };
>>> } __packed;
>>>
>>> sof_ipc_ctrl_value_chan and sof_ipc_ctrl_value_comp are of the same
>>> size - 8 bytes, while sof_abi_hdr is much larger - _at least_ 32 bytes
>>> (`__u32 data[0]` in sof_abi_hdr suggest that there should be more
>>> payload after header). But they all contribute 0 to sizeof(sof_ipc_ctrl_data).
>>>
>>> Now control data allocations looks as follows
>>>
>>> scontrol->size = struct_size(scontrol->control_data, chanv,
>>> le32_to_cpu(mc->num_channels));
>>> scontrol->control_data = kzalloc(scontrol->size, GFP_KERNEL);
>>>
>>> Which is sizeof(sof_ipc_ctrl_data) + mc->num_channels * sizeof(sof_ipc_ctrl_value_chan)
>>>
>>> For some reason it uses sizeof(sof_ipc_ctrl_value_chan), which is not
>>> the largest member of the union.
>>>
>>> And this is where the problem is: in order to make control->data.FOO loads
>>> and stores legal we need mc->num_channels to be of at least 4. So that
>>>
>>> sizeof(sof_ipc_ctrl_data) + mc->num_channels * sizeof(sof_ipc_ctrl_value_chan)
>>>
>>> 92 + 4 * 8
>>>
>>> will be the same as
>>>
>>> sizeof(sof_ipc_ctrl_data) + sizeof(sof_abi_hdr).
>>>
>>> 92 + 32
>>>
>>> Otherwise scontrol->control_data->data.FOO will access nearby/foreign
>>> slab object.
>>>
>>> And there is at least one such memory access. In sof_get_control_data().
>>>
>>> wdata[i].pdata = wdata[i].control->control_data->data;
>>> *size += wdata[i].pdata->size;
>>>
>>>
>>> pdata->size is at offset 8, but if, say, mc->num_channels == 1 then
>>> we allocate only 8 bytes for pdata, so pdata->size is 4 bytes outside
>>> of allocated slab object.
>>>
>>> Thoughts?
>
> Your analyzes are spot on, unfortunately. But...
>
> As of today, the sof_get_control_data() is in the call path of
> (ipc3-topology.c):
>
> sof_widget_update_ipc_comp_process() -> sof_process_load() ->
> sof_get_control_data()
>
> sof_widget_update_ipc_comp_process() is the ipc_setup callback for
> snd_soc_dapm_effect. If I'm not mistaken these only carries bin payload
> and never MIXER/ENUM/SWITCH/VOLUME.
> This means that the sof_get_control_data() is only called with
> SND_SOC_TPLG_TYPE_BYTES and for that the allocated data area is correct.
>
> This can explain why we have not seen any issues so far. This does not
> renders the code right, as how it is written atm is wrong.

Sergey's results with KASAN show that there's a real-life problem though. I also don't understand how that might happen.

Could it be that these results are with a specific topology where our assumptions are incorrect?