Re: [PATCH] ASoC: mediatek: Check num_codecs is not zero to avoid panic during probe

[Kuninori Morimoto <kuninori.morimoto.gx@xxxxxxxxxxx>]

Hi

> Following commit 13f58267cda3 ("ASoC: soc.h: don't create dummy
> Component via COMP_DUMMY()"), COMP_DUMMY() became an array with zero
> length, and only gets populated with the dummy struct after the card is
> registered. Since the sound card driver's probe happens before the card
> registration, accessing any of the members of a dummy component during
> probe will result in undefined behavior.
> 
> This can be observed in the mt8188 and mt8195 machine sound drivers. By
> omitting a dai link subnode in the sound card's node in the Devicetree,
> the default uninitialized dummy codec is used, and when its dai_name
> pointer gets passed to strcmp() it results in a null pointer dereference
> and a kernel panic.
> 
> In addition to that, set_card_codec_info() in the generic helpers file,
> mtk-soundcard-driver.c, will populate a dai link with a dummy codec when
> a dai link node is present in DT but with no codec property.
> 
> The result is that at probe time, a dummy codec can either be
> uninitialized with num_codecs = 0, or be an initialized dummy codec,
> with num_codecs = 1 and dai_name = "snd-soc-dummy-dai". In order to
> accommodate for both situations, check that num_codecs is not zero
> before accessing the codecs' fields but still check for the codec's dai
> name against "snd-soc-dummy-dai" as needed.
> 
> While at it, also drop the check that dai_name is not null in the mt8192
> driver, introduced in commit 4d4e1b6319e5 ("ASoC: mediatek: mt8192:
> Check existence of dai_name before dereferencing"), as it is actually
> redundant given the preceding num_codecs != 0 check.
> 
> Fixes: 13f58267cda3 ("ASoC: soc.h: don't create dummy Component via COMP_DUMMY()")
> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>

Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@xxxxxxxxxxx>

Thank you for your help !!

Best regards
---
Kuninori Morimoto