syzbot reported the following uninit-value access issue [1]:

smsc95xx 1-1:0.0 (unnamed net_device) (uninitialized): Failed to read reg index 0x00000030: -32
smsc95xx 1-1:0.0 (unnamed net_device) (uninitialized): Error reading E2P_CMD
=====================================================
BUG: KMSAN: uninit-value in smsc95xx_reset+0x409/0x25f0 drivers/net/usb/smsc95xx.c:896
 smsc95xx_reset+0x409/0x25f0 drivers/net/usb/smsc95xx.c:896
 smsc95xx_bind+0x9bc/0x22e0 drivers/net/usb/smsc95xx.c:1131
 usbnet_probe+0x100b/0x4060 drivers/net/usb/usbnet.c:1750
 usb_probe_interface+0xc75/0x1210 drivers/usb/core/driver.c:396
 really_probe+0x506/0xf40 drivers/base/dd.c:658
 __driver_probe_device+0x2a7/0x5d0 drivers/base/dd.c:800
 driver_probe_device+0x72/0x7b0 drivers/base/dd.c:830
 __device_attach_driver+0x55a/0x8f0 drivers/base/dd.c:958
 bus_for_each_drv+0x3ff/0x620 drivers/base/bus.c:457
 __device_attach+0x3bd/0x640 drivers/base/dd.c:1030
 device_initial_probe+0x32/0x40 drivers/base/dd.c:1079
 bus_probe_device+0x3d8/0x5a0 drivers/base/bus.c:532
 device_add+0x16ae/0x1f20 drivers/base/core.c:3622
 usb_set_configuration+0x31c9/0x38c0 drivers/usb/core/message.c:2207
 usb_generic_driver_probe+0x109/0x2a0 drivers/usb/core/generic.c:238
 usb_probe_device+0x290/0x4a0 drivers/usb/core/driver.c:293
 really_probe+0x506/0xf40 drivers/base/dd.c:658
 __driver_probe_device+0x2a7/0x5d0 drivers/base/dd.c:800
 driver_probe_device+0x72/0x7b0 drivers/base/dd.c:830
 __device_attach_driver+0x55a/0x8f0 drivers/base/dd.c:958
 bus_for_each_drv+0x3ff/0x620 drivers/base/bus.c:457
 __device_attach+0x3bd/0x640 drivers/base/dd.c:1030
 device_initial_probe+0x32/0x40 drivers/base/dd.c:1079
 bus_probe_device+0x3d8/0x5a0 drivers/base/bus.c:532
 device_add+0x16ae/0x1f20 drivers/base/core.c:3622
 usb_new_device+0x15f6/0x22f0 drivers/usb/core/hub.c:2589
 hub_port_connect drivers/usb/core/hub.c:5440 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5580 [inline]
 port_event drivers/usb/core/hub.c:5740 [inline]
 hub_event+0x53bc/0x7290 drivers/usb/core/hub.c:5822
 process_one_work kernel/workqueue.c:2630 [inline]
 process_scheduled_works+0x104e/0x1e70 kernel/workqueue.c:2703
 worker_thread+0xf45/0x1490 kernel/workqueue.c:2784
 kthread+0x3e8/0x540 kernel/kthread.c:388
 ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304

Local variable buf.i225 created at:
 smsc95xx_read_reg drivers/net/usb/smsc95xx.c:90 [inline]
 smsc95xx_reset+0x203/0x25f0 drivers/net/usb/smsc95xx.c:892
 smsc95xx_bind+0x9bc/0x22e0 drivers/net/usb/smsc95xx.c:1131

CPU: 1 PID: 773 Comm: kworker/1:2 Not tainted 6.6.0-rc1-syzkaller-00125-ge42bebf6 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/04/2023
Workqueue: usb_hub_wq hub_event
=====================================================

Similar to e9c65989 ("net: usb: smsc75xx: Fix uninit-value access in
__smsc75xx_read_reg"), this issue is caused because usbnet_read_cmd() reads
less bytes than requested (zero byte in the reproducer). In this case,
'buf' is not properly filled.

This patch fixes the issue by returning -ENODATA if usbnet_read_cmd() reads
less bytes than requested.

sysbot reported similar uninit-value access issue [2]. The root cause is
the same as mentioned above, and this patch addresses it as well.

Fixes: 2f7ca802 ("net: Add SMSC LAN9500 USB2.0 10/100 ethernet adapter driver")
Reported-and-tested-by: syzbot+c74c24b43c9ae534f0e0@syzkaller.appspotmail.com
Reported-and-tested-by: syzbot+2c97a98a5ba9ea9c23bd@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c74c24b43c9ae534f0e0 [1]
Closes: https://syzkaller.appspot.com/bug?extid=2c97a98a5ba9ea9c23bd [2]
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>