linux-kernel - [PATCH 4.9 025/218] ALSA: cs4236: fix an incorrect NULL check on list iterator

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Date:   Mon, 18 Apr 2022 14:11:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xiaomeng Tong <xiam0nd.tong@...il.com>,
        Takashi Iwai <tiwai@...e.de>
Subject: [PATCH 4.9 025/218] ALSA: cs4236: fix an incorrect NULL check on list iterator

From: Xiaomeng Tong <xiam0nd.tong@...il.com>

commit 0112f822f8a6d8039c94e0bc9b264d7ffc5d4704 upstream.

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>
Link: https://lore.kernel.org/r/20220327060822.4735-1-xiam0nd.tong@gmail.com
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 sound/isa/cs423x/cs4236.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/sound/isa/cs423x/cs4236.c
+++ b/sound/isa/cs423x/cs4236.c
@@ -557,7 +557,7 @@ static int snd_cs423x_pnpbios_detect(str
 	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))
@@ -573,9 +573,11 @@ static int snd_cs423x_pnpbios_detect(str
 	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)