linux-kernel - [PATCH 3.16.y-ckt 081/135] ASoC: simple-card: Fix crash in asoc_simple_card

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Message-Id: <1423224113-10958-82-git-send-email-luis.henriques@canonical.com>
Date:	Fri,  6 Feb 2015 12:00:59 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Geert Uytterhoeven <geert+renesas@...der.be>,
	Mark Brown <broonie@...nel.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 081/135] ASoC: simple-card: Fix crash in asoc_simple_card_unref()

3.16.7-ckt6 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Geert Uytterhoeven <geert+renesas@...der.be>

commit 7ddfdb5c5a5b51bdd2cb749d8341d763b079d520 upstream.

If asoc_simple_card_probe() fails, asoc_simple_card_unref() may be
called before dev_set_drvdata(), causing a NULL pointer dereference in
asoc_simple_card_unref():

    Unable to handle kernel NULL pointer dereference at virtual address 000000d4
    ...
    PC is at asoc_simple_card_unref+0x14/0x48
    LR is at asoc_simple_card_probe+0x3d4/0x40c

This typically happens because asoc_simple_card_parse_of() returns
-EPROBE_DEFER, but other failure modes are possible.
devm_snd_soc_register_card()/snd_soc_register_card() may fail either
before or after dev_set_drvdata().

Pass a snd_soc_card pointer instead of a platform_device pointer to
asoc_simple_card_unref() to fix this.

Note that if CONFIG_OF_DYNAMIC=n, of_node_put() is a dummy, and gcc may
optimize away the loop over card->dai_link, never actually dereferencing
card, and thus avoiding the crash...

Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
Fixes: e512e001dafa54e5 ("ASoC: simple-card: Fix the reference count of device nodes")
Signed-off-by: Mark Brown <broonie@...nel.org>
[ luis: backported to 3.16:
  - adjusted context
  - dropped changes to asoc_simple_card_remove() ]
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 sound/soc/generic/simple-card.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/sound/soc/generic/simple-card.c b/sound/soc/generic/simple-card.c
index 03a7fdcdf114..517a0ff64303 100644
--- a/sound/soc/generic/simple-card.c
+++ b/sound/soc/generic/simple-card.c
@@ -357,9 +357,8 @@ static int asoc_simple_card_parse_of(struct device_node *node,
 }
 
 /* update the reference count of the devices nodes at end of probe */
-static int asoc_simple_card_unref(struct platform_device *pdev)
+static int asoc_simple_card_unref(struct snd_soc_card *card)
 {
-	struct snd_soc_card *card = platform_get_drvdata(pdev);
 	struct snd_soc_dai_link *dai_link;
 	struct device_node *np;
 	int num_links;
@@ -482,7 +481,7 @@ static int asoc_simple_card_probe(struct platform_device *pdev)
 	ret = devm_snd_soc_register_card(&pdev->dev, &priv->snd_card);
 
 err:
-	asoc_simple_card_unref(pdev);
+	asoc_simple_card_unref(&priv->snd_card);
 	return ret;
 }
 
-- 
2.1.4

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