Re: [Sound-open-firmware] out-of-bounds access in sound/soc/sof/topology.c

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.

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?

The SOF contributors who wrote that code are all on an extended Easter week-end or vacation so we'll need more time to provide a definitive answer.

I am far from an expert on the topology, but I note that the 'data' field is only used for binary controls, where we use the maximum possible size for a control, without any arithmetic involving channels. It makes sense to me, the binary data does not have any defined structure, it's just a bunch of bytes provided as is to the firmware.

static int sof_ipc3_control_load_bytes(struct snd_sof_dev *sdev, struct snd_sof_control *scontrol) { struct sof_ipc_ctrl_data *cdata; int ret;

scontrol->ipc_control_data = kzalloc(scontrol->max_size, GFP_KERNEL); if (!scontrol->ipc_control_data) return -ENOMEM;

In other cases, such as volumes and enums, the 'data' field doesn't seem to be used but we do use the channel information for volume and enums.

static int sof_ipc3_control_load_volume(struct snd_sof_dev *sdev, struct snd_sof_control *scontrol) { struct sof_ipc_ctrl_data *cdata; int i;

/* init the volume get/put data */ scontrol->size = struct_size(cdata, chanv, scontrol->num_channels);

scontrol->ipc_control_data = kzalloc(scontrol->size, GFP_KERNEL);

static int sof_ipc3_control_load_enum(struct snd_sof_dev *sdev, struct snd_sof_control *scontrol) { struct sof_ipc_ctrl_data *cdata;

/* init the enum get/put data */ scontrol->size = struct_size(cdata, chanv, scontrol->num_channels);

scontrol->ipc_control_data = kzalloc(scontrol->size, GFP_KERNEL); if (!scontrol->ipc_control_data)

Given that we have two ways of allocating the memory, I am not sure there is a problem, but I could be wrong.

I checked the v5.10.111 code and I see the same code, with the max_size being used for sof_control_load_bytes() and no channel-based arithmetic.

Can I ask how you found out about this problem, is this the result of a warning/error reported by a software tool or based on your reviews of the code?

Thanks -Pierre