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SubjectRe: [PATCH] ASoC: topology: Avoid card NULL deref in snd_soc_tplg_component_remove()
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On 6/3/2022 10:14 PM, Dean Gehnert wrote:
> 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@gmail.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Jaroslav Kysela <perex@perex.cz>
> Cc: Takashi Iwai <tiwai@suse.com>
> Cc: alsa-devel@alsa-project.org
> Cc: linux-kernel@vger.kernel.org
> Cc: stable@vger.kernel.org
> Fixes: 7e567b5ae063 ("ASoC: topology: Add missing rwsem around snd_ctl_remove() calls")
> Signed-off-by: Dean Gehnert <deang@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) {

I'm pretty sure that quite a lot of operations in this
list_for_each_entry_safe() loop require existing card...

And trying to investigate more closely, there is no
soc_cleanup_component() mentioned in commit message, for quite a few
kernel versions - seems to have been removed during v5.5-rc1.

I would say to not merge this, unless problem can be reproduced with
latest kernel and even then would consider if it is a correct fix.

>
> @@ -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 */

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