linux-kernel - Re: [PATCH] soc: soc-core: fix a missing check on list iterator

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Date:   Sun, 27 Mar 2022 23:31:19 +0000
From:   Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>
Cc:     lgirdwood@...il.com, broonie@...nel.org, perex@...ex.cz,
        tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] soc: soc-core: fix a missing check on list iterator


Hi Xiaomeng

Thank you for your patch

> The bug is here:
> 	*dai_name = dai->driver->name;
> 
> For for_each_component_dais, just like list_for_each_entry,
> the list iterator 'dai' will point to a bogus position
> containing HEAD if the list is empty or no element is found.
> This case must be checked before any use of the iterator,
> otherwise it will lead to a invalid memory access.
> 
> To fix the bug, use a new variable 'iter' as the list iterator,
> while use the original variable 'dai' as a dedicated pointer
> to point to the found element.
> 
> Cc: stable@...r.kernel.org
> Fixes: 58bf4179000a3 ("ASoC: soc-core: remove dai_drv from snd_soc_component")
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
> ---

>From "code" point of view, indeed current code doesn't care non-find case,
but from "logic" point of view, it should find target DAI here.

If it couldn't find the DAI, it means
"This is the target component, but it doesn't have target DAI",
and it is very strange for me.

If you got such bug, it is CPU or Codec driver side bug, I think.
If this is for security reason, indicating such message somewhere
(for example by /* comment */) is nice idea for me.

Thank you for your help !!

Best regards
---
Kuninori Morimoto