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 * 8will be the same as
sizeof(sof_ipc_ctrl_data) + sizeof(sof_abi_hdr).
92 + 32Otherwise 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?