asix: fix uninit-value in asix_mdio_read()

JIRA: https://issues.redhat.com/browse/RHEL-28110
CVE: CVE-2021-47101

commit 8035b1a
Author: Pavel Skripkin <paskripkin@gmail.com>
Date:   Tue Dec 21 23:10:36 2021 +0300

    asix: fix uninit-value in asix_mdio_read()

    asix_read_cmd() may read less than sizeof(smsr) bytes and in this case
    smsr will be uninitialized.

    Fail log:
    BUG: KMSAN: uninit-value in asix_check_host_enable drivers/net/usb/asix_common.c:82 [inline]
    BUG: KMSAN: uninit-value in asix_check_host_enable drivers/net/usb/asix_common.c:82 [inline] drivers/net/usb/asix_common.c:497
    BUG: KMSAN: uninit-value in asix_mdio_read+0x3c1/0xb00 drivers/net/usb/asix_common.c:497 drivers/net/usb/asix_common.c:497
     asix_check_host_enable drivers/net/usb/asix_common.c:82 [inline]
     asix_check_host_enable drivers/net/usb/asix_common.c:82 [inline] drivers/net/usb/asix_common.c:497
     asix_mdio_read+0x3c1/0xb00 drivers/net/usb/asix_common.c:497 drivers/net/usb/asix_common.c:497

    Fixes: d9fe64e ("net: asix: Add in_pm parameter")
    Reported-and-tested-by: syzbot+f44badb06036334e867a@syzkaller.appspotmail.com
    Reviewed-by: Andrew Lunn <andrew@lunn.ch>
    Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
    Link: https://lore.kernel.org/r/8966e3b514edf39857dd93603fc79ec02e000a75.1640117288.git.paskripkin@gmail.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Ken Cox <jkc@redhat.com>

Author: Ken Cox

drivers/net/usb/asix_common.c

@@ -77,7 +77,7 @@ static int asix_check_host_enable(struct usbnet *dev, int in_pm)
 				    0, 0, 1, &smsr, in_pm);
 		if (ret == -ENODEV)
 			break;
-		else if (ret < 0)
+		else if (ret < sizeof(smsr))
 			continue;
 		else if (smsr & AX_HOST_EN)
 			break;