net: pegasus: fix uninit-value in get_interrupt_interval

Syzbot reported uninit value pegasus_probe(). The problem was in missing
error handling.

get_interrupt_interval() internally calls read_eprom_word() which can
fail in some cases. For example: failed to receive usb control message.
These cases should be handled to prevent uninit value bug, since
read_eprom_word() will not initialize passed stack variable in case of
internal failure.

Fail log:

BUG: KMSAN: uninit-value in get_interrupt_interval drivers/net/usb/pegasus.c:746 [inline]
BUG: KMSAN: uninit-value in pegasus_probe+0x10e7/0x4080 drivers/net/usb/pegasus.c:1152
CPU: 1 PID: 825 Comm: kworker/1:1 Not tainted 5.12.0-rc6-syzkaller #0
...
Workqueue: usb_hub_wq hub_event
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x24c/0x2e0 lib/dump_stack.c:120
 kmsan_report+0xfb/0x1e0 mm/kmsan/kmsan_report.c:118
 __msan_warning+0x5c/0xa0 mm/kmsan/kmsan_instr.c:197
 get_interrupt_interval drivers/net/usb/pegasus.c:746 [inline]
 pegasus_probe+0x10e7/0x4080 drivers/net/usb/pegasus.c:1152
....

Local variable ----data.i@pegasus_probe created at:
 get_interrupt_interval drivers/net/usb/pegasus.c:1151 [inline]
 pegasus_probe+0xe57/0x4080 drivers/net/usb/pegasus.c:1152
 get_interrupt_interval drivers/net/usb/pegasus.c:1151 [inline]
 pegasus_probe+0xe57/0x4080 drivers/net/usb/pegasus.c:1152

Reported-and-tested-by: syzbot+02c9f70f3afae308464a@syzkaller.appspotmail.com
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Link: https://lore.kernel.org/r/20210804143005.439-1-paskripkin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/usb/pegasus.c

@@ -744,12 +744,16 @@ static inline void disable_net_traffic(pegasus_t *pegasus)
 	set_registers(pegasus, EthCtrl0, sizeof(tmp), &tmp);
 }
 
-static inline void get_interrupt_interval(pegasus_t *pegasus)
+static inline int get_interrupt_interval(pegasus_t *pegasus)
 {
 	u16 data;
 	u8 interval;
+	int ret;
+
+	ret = read_eprom_word(pegasus, 4, &data);
+	if (ret < 0)
+		return ret;
 
-	read_eprom_word(pegasus, 4, &data);
 	interval = data >> 8;
 	if (pegasus->usb->speed != USB_SPEED_HIGH) {
 		if (interval < 0x80) {
@@ -764,6 +768,8 @@ static inline void get_interrupt_interval(pegasus_t *pegasus)
 		}
 	}
 	pegasus->intr_interval = interval;
+
+	return 0;
 }
 
 static void set_carrier(struct net_device *net)
@@ -1165,7 +1171,9 @@ static int pegasus_probe(struct usb_interface *intf,
 				| NETIF_MSG_PROBE | NETIF_MSG_LINK);
 
 	pegasus->features = usb_dev_id[dev_index].private;
-	get_interrupt_interval(pegasus);
+	res = get_interrupt_interval(pegasus);
+	if (res)
+		goto out2;
 	if (reset_mac(pegasus)) {
 		dev_err(&intf->dev, "can't reset MAC\n");
 		res = -EIO;