When devm runs function in the "remove" path for a device it runs them
in the reverse order. That means that if you have parts of your driver
that aren't using devm or are using "roll your own" devm w/
devm_add_action_or_reset() you need to keep that in mind.

The mt8186 audio driver didn't quite get this right. Specifically, in
mt8186_init_clock() it called mt8186_audsys_clk_register() and then
went on to call a bunch of other devm function. The caller of
mt8186_init_clock() used devm_add_action_or_reset() to call
mt8186_deinit_clock() but, because of the intervening devm functions,
the order was wrong.

Specifically at probe time, the order was:
1. mt8186_audsys_clk_register()
2. afe_priv->clk = devm_kcalloc(...)
3. afe_priv->clk[i] = devm_clk_get(...)

At remove time, the order (which should have been 3, 2, 1) was:
1. mt8186_audsys_clk_unregister()
3. Free all of afe_priv->clk[i]
2. Free afe_priv->clk

The above seemed to be causing a use-after-free. Luckily, it's easy to
fix this by simply using devm more correctly. Let's move the
devm_add_action_or_reset() to the right place. In addition to fixing
the use-after-free, code inspection shows that this fixes a leak
(missing call to mt8186_audsys_clk_unregister()) that would have
happened if any of the syscon_regmap_lookup_by_phandle() calls in
mt8186_init_clock() had failed.

Fixes: 55b423d5623c ("ASoC: mediatek: mt8186: support audio clock control in platform driver")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 sound/soc/mediatek/mt8186/mt8186-afe-clk.c    |  6 ---
 sound/soc/mediatek/mt8186/mt8186-afe-clk.h    |  1 -
 sound/soc/mediatek/mt8186/mt8186-afe-pcm.c    |  4 --
 sound/soc/mediatek/mt8186/mt8186-audsys-clk.c | 46 ++++++++++---------
 sound/soc/mediatek/mt8186/mt8186-audsys-clk.h |  1 -
 5 files changed, 24 insertions(+), 34 deletions(-)

diff --git a/sound/soc/mediatek/mt8186/mt8186-afe-clk.c b/sound/soc/mediatek/mt8186/mt8186-afe-clk.c
index a6b4f29049bb..539e3a023bc4 100644
--- a/sound/soc/mediatek/mt8186/mt8186-afe-clk.c
+++ b/sound/soc/mediatek/mt8186/mt8186-afe-clk.c
@@ -644,9 +644,3 @@ int mt8186_init_clock(struct mtk_base_afe *afe)
 
 	return 0;
 }
-
-void mt8186_deinit_clock(void *priv)
-{
-	struct mtk_base_afe *afe = priv;
-	mt8186_audsys_clk_unregister(afe);
-}
diff --git a/sound/soc/mediatek/mt8186/mt8186-afe-clk.h b/sound/soc/mediatek/mt8186/mt8186-afe-clk.h
index d5988717d8f2..a9d59e506d9a 100644
--- a/sound/soc/mediatek/mt8186/mt8186-afe-clk.h
+++ b/sound/soc/mediatek/mt8186/mt8186-afe-clk.h
@@ -81,7 +81,6 @@ enum {
 struct mtk_base_afe;
 int mt8186_set_audio_int_bus_parent(struct mtk_base_afe *afe, int clk_id);
 int mt8186_init_clock(struct mtk_base_afe *afe);
-void mt8186_deinit_clock(void *priv);
 int mt8186_afe_enable_cgs(struct mtk_base_afe *afe);
 void mt8186_afe_disable_cgs(struct mtk_base_afe *afe);
 int mt8186_afe_enable_clock(struct mtk_base_afe *afe);
diff --git a/sound/soc/mediatek/mt8186/mt8186-afe-pcm.c b/sound/soc/mediatek/mt8186/mt8186-afe-pcm.c
index 41172a82103e..a868a04ed4e7 100644
--- a/sound/soc/mediatek/mt8186/mt8186-afe-pcm.c
+++ b/sound/soc/mediatek/mt8186/mt8186-afe-pcm.c
@@ -2848,10 +2848,6 @@ static int mt8186_afe_pcm_dev_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	ret = devm_add_action_or_reset(dev, mt8186_deinit_clock, (void *)afe);
-	if (ret)
-		return ret;
-
 	/* init memif */
 	afe->memif_32bit_supported = 0;
 	afe->memif_size = MT8186_MEMIF_NUM;
diff --git a/sound/soc/mediatek/mt8186/mt8186-audsys-clk.c b/sound/soc/mediatek/mt8186/mt8186-audsys-clk.c
index 578969ca91c8..5666be6b1bd2 100644
--- a/sound/soc/mediatek/mt8186/mt8186-audsys-clk.c
+++ b/sound/soc/mediatek/mt8186/mt8186-audsys-clk.c
@@ -84,6 +84,29 @@ static const struct afe_gate aud_clks[CLK_AUD_NR_CLK] = {
 	GATE_AUD2(CLK_AUD_ETDM_OUT1_BCLK, "aud_etdm_out1_bclk", "top_audio", 24),
 };
 
+static void mt8186_audsys_clk_unregister(void *data)
+{
+	struct mtk_base_afe *afe = data;
+	struct mt8186_afe_private *afe_priv = afe->platform_priv;
+	struct clk *clk;
+	struct clk_lookup *cl;
+	int i;
+
+	if (!afe_priv)
+		return;
+
+	for (i = 0; i < CLK_AUD_NR_CLK; i++) {
+		cl = afe_priv->lookup[i];
+		if (!cl)
+			continue;
+
+		clk = cl->clk;
+		clk_unregister_gate(clk);
+
+		clkdev_drop(cl);
+	}
+}
+
 int mt8186_audsys_clk_register(struct mtk_base_afe *afe)
 {
 	struct mt8186_afe_private *afe_priv = afe->platform_priv;
@@ -124,27 +147,6 @@ int mt8186_audsys_clk_register(struct mtk_base_afe *afe)
 		afe_priv->lookup[i] = cl;
 	}
 
-	return 0;
+	return devm_add_action_or_reset(afe->dev, mt8186_audsys_clk_unregister, afe);
 }
 
-void mt8186_audsys_clk_unregister(struct mtk_base_afe *afe)
-{
-	struct mt8186_afe_private *afe_priv = afe->platform_priv;
-	struct clk *clk;
-	struct clk_lookup *cl;
-	int i;
-
-	if (!afe_priv)
-		return;
-
-	for (i = 0; i < CLK_AUD_NR_CLK; i++) {
-		cl = afe_priv->lookup[i];
-		if (!cl)
-			continue;
-
-		clk = cl->clk;
-		clk_unregister_gate(clk);
-
-		clkdev_drop(cl);
-	}
-}
diff --git a/sound/soc/mediatek/mt8186/mt8186-audsys-clk.h b/sound/soc/mediatek/mt8186/mt8186-audsys-clk.h
index b8d6a06e11e8..897a2914dc19 100644
--- a/sound/soc/mediatek/mt8186/mt8186-audsys-clk.h
+++ b/sound/soc/mediatek/mt8186/mt8186-audsys-clk.h
@@ -10,6 +10,5 @@
 #define _MT8186_AUDSYS_CLK_H_
 
 int mt8186_audsys_clk_register(struct mtk_base_afe *afe);
-void mt8186_audsys_clk_unregister(struct mtk_base_afe *afe);
 
 #endif
-- 
2.40.1.606.ga4b1b128d6-goog

On Thu, 11 May 2023 09:25:12 -0700, Douglas Anderson wrote:
> When devm runs function in the "remove" path for a device it runs them
> in the reverse order. That means that if you have parts of your driver
> that aren't using devm or are using "roll your own" devm w/
> devm_add_action_or_reset() you need to keep that in mind.
> 
> The mt8186 audio driver didn't quite get this right. Specifically, in
> mt8186_init_clock() it called mt8186_audsys_clk_register() and then
> went on to call a bunch of other devm function. The caller of
> mt8186_init_clock() used devm_add_action_or_reset() to call
> mt8186_deinit_clock() but, because of the intervening devm functions,
> the order was wrong.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-next

Thanks!

[1/1] ASoC: mediatek: mt8186: Fix use-after-free in driver remove path
      commit: a93d2afd3f77a7331271a0f25c6a11003db69b3c

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark