ASoC: dapm: Fix UAF for snd_soc_pcm_runtime object

When using kernel with the following extra config,

  - CONFIG_KASAN=y
  - CONFIG_KASAN_GENERIC=y
  - CONFIG_KASAN_INLINE=y
  - CONFIG_KASAN_VMALLOC=y
  - CONFIG_FRAME_WARN=4096

kernel detects that snd_pcm_suspend_all() access a freed
'snd_soc_pcm_runtime' object when the system is suspended, which
leads to a use-after-free bug:

[   52.047746] BUG: KASAN: use-after-free in snd_pcm_suspend_all+0x1a8/0x270
[   52.047765] Read of size 1 at addr ffff0000b9434d50 by task systemd-sleep/2330

[   52.047785] Call trace:
[   52.047787]  dump_backtrace+0x0/0x3c0
[   52.047794]  show_stack+0x34/0x50
[   52.047797]  dump_stack_lvl+0x68/0x8c
[   52.047802]  print_address_description.constprop.0+0x74/0x2c0
[   52.047809]  kasan_report+0x210/0x230
[   52.047815]  __asan_report_load1_noabort+0x3c/0x50
[   52.047820]  snd_pcm_suspend_all+0x1a8/0x270
[   52.047824]  snd_soc_suspend+0x19c/0x4e0

The snd_pcm_sync_stop() has a NULL check on 'substream->runtime' before
making any access. So we need to always set 'substream->runtime' to NULL
everytime we kfree() it.

Fixes: a72706ed ("ASoC: codec2codec: remove ephemeral variables")
Signed-off-by: robelin <robelin@nvidia.com>
Signed-off-by: Sameer Pujar <spujar@nvidia.com>
Link: https://patch.msgid.link/20240823144342.4123814-2-spujar@nvidia.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/soc-dapm.c

@@ -4057,6 +4057,7 @@ static int snd_soc_dai_link_event(struct snd_soc_dapm_widget *w,
 
 	case SND_SOC_DAPM_POST_PMD:
 		kfree(substream->runtime);
+		substream->runtime = NULL;
 		break;
 
 	default: