Re: [PATCH] soundwire: stream: fix NULL pointer dereference for multi_link

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 11/24/23 12:01, Krzysztof Kozlowski wrote:
> If bus is marked as multi_link, but number of masters in the stream is
> not higher than bus->hw_sync_min_links (bus->multi_link && m_rt_count >=
> bus->hw_sync_min_links), bank switching should not happen.  The first
> part of do_bank_switch() code properly takes these conditions into
> account, but second part (sdw_ml_sync_bank_switch()) relies purely on
> bus->multi_link property.  This is not balanced and leads to NULL
> pointer dereference:
> 
>   Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
>   ...
>   Call trace:
>    wait_for_completion_timeout+0x124/0x1f0
>    do_bank_switch+0x370/0x6f8
>    sdw_prepare_stream+0x2d0/0x438
>    qcom_snd_sdw_prepare+0xa0/0x118
>    sm8450_snd_prepare+0x128/0x148
>    snd_soc_link_prepare+0x5c/0xe8
>    __soc_pcm_prepare+0x28/0x1ec
>    dpcm_be_dai_prepare+0x1e0/0x2c0
>    dpcm_fe_dai_prepare+0x108/0x28c
>    snd_pcm_do_prepare+0x44/0x68
>    snd_pcm_action_single+0x54/0xc0
>    snd_pcm_action_nonatomic+0xe4/0xec
>    snd_pcm_prepare+0xc4/0x114
>    snd_pcm_common_ioctl+0x1154/0x1cc0
>    snd_pcm_ioctl+0x54/0x74
> 
> Fixes: ce6e74d008ff ("soundwire: Add support for multi link bank switch")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

LGTM, thanks for the patch.

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>


> ---
>  drivers/soundwire/stream.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
> index 9dc6399f206a..f9c0adc0738d 100644
> --- a/drivers/soundwire/stream.c
> +++ b/drivers/soundwire/stream.c
> @@ -742,14 +742,15 @@ static int sdw_bank_switch(struct sdw_bus *bus, int m_rt_count)
>   * sdw_ml_sync_bank_switch: Multilink register bank switch
>   *
>   * @bus: SDW bus instance
> + * @multi_link: whether this is a multi-link stream with hardware-based sync
>   *
>   * Caller function should free the buffers on error
>   */
> -static int sdw_ml_sync_bank_switch(struct sdw_bus *bus)
> +static int sdw_ml_sync_bank_switch(struct sdw_bus *bus, bool multi_link)
>  {
>  	unsigned long time_left;
>  
> -	if (!bus->multi_link)
> +	if (!multi_link)
>  		return 0;
>  
>  	/* Wait for completion of transfer */
> @@ -847,7 +848,7 @@ static int do_bank_switch(struct sdw_stream_runtime *stream)
>  			bus->bank_switch_timeout = DEFAULT_BANK_SWITCH_TIMEOUT;
>  
>  		/* Check if bank switch was successful */
> -		ret = sdw_ml_sync_bank_switch(bus);
> +		ret = sdw_ml_sync_bank_switch(bus, multi_link);
>  		if (ret < 0) {
>  			dev_err(bus->dev,
>  				"multi link bank switch failed: %d\n", ret);