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

Sergey Senozhatsky
2022-04-15T09:23:58Z

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?