ALSA: cs4236: fix an incorrect NULL check on list iterator

stable inclusion
from stable-v5.10.110
commit a55e2d74232f63e411d979d0141009ba03e16d97
bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a55e2d74232f63e411d979d0141009ba03e16d97

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

commit 0112f822 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@vger.kernel.org
Fixes: c2b73d14 ("ALSA: cs4236: cs4232 and cs4236 driver merge to solve PnP BIOS detection")
Signed-off-by: NXiaomeng Tong <xiam0nd.tong@gmail.com>
Link: https://lore.kernel.org/r/20220327060822.4735-1-xiam0nd.tong@gmail.comSigned-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

sound/isa/cs423x/cs4236.c

@@ -544,7 +544,7 @@ 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))
@@ -560,9 +560,11 @@ 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)