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);