[PATCH] ASoC: topology: Avoid card NULL deref in snd_soc_tplg_component_remove()

[Dean Gehnert]

Don't deference card in comp->card->snd_card before checking for NULL card.

During the unloading of ASoC kernel modules, there is a kernel oops in
snd_soc_tplg_component_remove() that happens because comp->card is set to
NULL in soc_cleanup_component().

Cc: Liam Girdwood <lgirdwood at gmail.com>
Cc: Mark Brown <broonie at kernel.org>
Cc: Jaroslav Kysela <perex at perex.cz>
Cc: Takashi Iwai <tiwai at suse.com>
Cc: alsa-devel at alsa-project.org
Cc: linux-kernel at vger.kernel.org
Cc: stable at vger.kernel.org
Fixes: 7e567b5ae063 ("ASoC: topology: Add missing rwsem around snd_ctl_remove() calls")
Signed-off-by: Dean Gehnert <deang at tpi.com>
---
 sound/soc/soc-topology.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/sound/soc/soc-topology.c b/sound/soc/soc-topology.c
index 3f9d314fba16..cf0efe1147c2 100644
--- a/sound/soc/soc-topology.c
+++ b/sound/soc/soc-topology.c
@@ -2613,15 +2613,18 @@ EXPORT_SYMBOL_GPL(snd_soc_tplg_component_load);
 /* remove dynamic controls from the component driver */
 int snd_soc_tplg_component_remove(struct snd_soc_component *comp)
 {
-	struct snd_card *card = comp->card->snd_card;
+	struct snd_card *card;
 	struct snd_soc_dobj *dobj, *next_dobj;
 	int pass;
 
 	/* process the header types from end to start */
 	for (pass = SOC_TPLG_PASS_END; pass >= SOC_TPLG_PASS_START; pass--) {
 
+		card = (comp->card) ? comp->card->snd_card : NULL;
+
 		/* remove mixer controls */
-		down_write(&card->controls_rwsem);
+		if (card)
+			down_write(&card->controls_rwsem);
 		list_for_each_entry_safe(dobj, next_dobj, &comp->dobj_list,
 			list) {
 
@@ -2660,7 +2663,8 @@ int snd_soc_tplg_component_remove(struct snd_soc_component *comp)
 				break;
 			}
 		}
-		up_write(&card->controls_rwsem);
+		if (card)
+			up_write(&card->controls_rwsem);
 	}
 
 	/* let caller know if FW can be freed when no objects are left */
-- 
2.17.1