linux-kernel - [PATCH] cs423x: cs4236: fix an incorrect NULL check on list iterator

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Message-Id: <20220327060822.4735-1-xiam0nd.tong@gmail.com>
Date:   Sun, 27 Mar 2022 14:08:22 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     perex@...ex.cz
Cc:     tiwai@...e.com, krzysztof.h1@...pl, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org,
        Xiaomeng Tong <xiam0nd.tong@...il.com>, stable@...r.kernel.org
Subject: [PATCH] cs423x: cs4236: fix an incorrect NULL check on list iterator

The bug is here:
	err = snd_card_cs423x_pnp(dev, card->private_data, pdev, cdev);

The list iterator value 'cdev' will *always* be set and non-NULL
by list_for_each_entry(), so it is incorrect to assume that the
iterator value will be NULL if the list is empty or no element
is found.

To fix the bug, use a new variable 'iter' as the list iterator,
while use the original variable 'cdev' as a dedicated pointer
to point to the found element. And snd_card_cs423x_pnp() itself
has NULL check for cdev.

Cc: stable@...r.kernel.org
Fixes: c2b73d1458014 ("ALSA: cs4236: cs4232 and cs4236 driver merge to solve PnP BIOS detection")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
---
 sound/isa/cs423x/cs4236.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/sound/isa/cs423x/cs4236.c b/sound/isa/cs423x/cs4236.c
index b6bdebd9ef27..10112e1bb25d 100644
--- a/sound/isa/cs423x/cs4236.c
+++ b/sound/isa/cs423x/cs4236.c
@@ -494,7 +494,7 @@ static int snd_cs423x_pnpbios_detect(struct pnp_dev *pdev,
 	static int dev;
 	int err;
 	struct snd_card *card;
-	struct pnp_dev *cdev;
+	struct pnp_dev *cdev, *iter;
 	char cid[PNP_ID_LEN];
 
 	if (pnp_device_is_isapnp(pdev))
@@ -510,9 +510,11 @@ static int snd_cs423x_pnpbios_detect(struct pnp_dev *pdev,
 	strcpy(cid, pdev->id[0].id);
 	cid[5] = '1';
 	cdev = NULL;
-	list_for_each_entry(cdev, &(pdev->protocol->devices), protocol_list) {
-		if (!strcmp(cdev->id[0].id, cid))
+	list_for_each_entry(iter, &(pdev->protocol->devices), protocol_list) {
+		if (!strcmp(iter->id[0].id, cid)) {
+			cdev = iter;
 			break;
+		}
 	}
 	err = snd_cs423x_card_new(&pdev->dev, dev, &card);
 	if (err < 0)
-- 
2.17.1