[PATCH AUTOSEL 5.15 33/44] ASoC: core: Check for rtd == NULL in snd_soc_remove_pcm_runtime()

[Sasha Levin <sashal@kernel.org>]

From: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>

[ Upstream commit 2d91cb261cac6d885954b8f5da28b5c176c18131 ]

snd_soc_remove_pcm_runtime() might be called with rtd == NULL which will
leads to null pointer dereference.
This was reproduced with topology loading and marking a link as ignore
due to missing hardware component on the system.
On module removal the soc_tplg_remove_link() would call
snd_soc_remove_pcm_runtime() with rtd == NULL since the link was ignored,
no runtime was created.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Liam Girdwood <liam.r.girdwood@intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://patch.msgid.link/20250619084222.559-3-peter.ujfalusi@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

**YES**

This commit should be backported to stable kernel trees. The analysis
reveals this is a critical NULL pointer dereference fix that prevents
kernel crashes.

**Key reasons for backporting:**

1. **Fixes a Real Crash**: The commit adds a NULL check to prevent a
   kernel panic that occurs when `snd_soc_remove_pcm_runtime()` is
   called with `rtd == NULL`. The code change shows this clearly:
```c
+   if (!rtd)
+       return;
```
Without this check, the subsequent line
`snd_soc_card_remove_dai_link(card, rtd->dai_link)` would dereference
NULL.

2. **Minimal and Safe Fix**: The change is extremely small (3 lines) and
   defensive - it simply adds a NULL check with early return. This
   follows the stable kernel rule of minimal, contained fixes.

3. **Affects Production Systems**: The commit message indicates this
   occurs during topology loading when hardware components are missing -
   a real-world scenario. The issue manifests on module removal when
   `soc_tplg_remove_link()` calls the function with NULL.

4. **Well-Reviewed**: The commit has 5 Reviewed-by tags from Intel ASoC
   maintainers, indicating thorough review and consensus on the fix.

5. **No Side Effects**: The fix has no architectural changes or new
   features - it purely adds defensive programming to prevent crashes.
   The function already had EXPORT_SYMBOL_GPL, indicating it's part of
   the kernel API that could be called from various contexts.

This is exactly the type of commit stable trees want: a small, obvious
fix for a real crash scenario with no risk of regression.

 sound/soc/soc-core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index 1c4d8b96f77b..d28261ef1d4c 100644
--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -959,6 +959,9 @@ static int soc_dai_link_sanity_check(struct snd_soc_card *card,
 void snd_soc_remove_pcm_runtime(struct snd_soc_card *card,
 				struct snd_soc_pcm_runtime *rtd)
 {
+	if (!rtd)
+		return;
+
 	lockdep_assert_held(&client_mutex);
 
 	/* release machine specific resources */
-- 
2.39.5