net: usb: aqc111: fix error handling of usbnet read calls

Syzkaller, courtesy of syzbot, identified an error (see report [1]) in
aqc111 driver, caused by incomplete sanitation of usb read calls'
results. This problem is quite similar to the one fixed in commit
920a9fa27e78 ("net: asix: add proper error handling of usb read errors").

For instance, usbnet_read_cmd() may read fewer than 'size' bytes,
even if the caller expected the full amount, and aqc111_read_cmd()
will not check its result properly. As [1] shows, this may lead
to MAC address in aqc111_bind() being only partly initialized,
triggering KMSAN warnings.

Fix the issue by verifying that the number of bytes read is
as expected and not less.

[1] Partial syzbot report:
BUG: KMSAN: uninit-value in is_valid_ether_addr include/linux/etherdevice.h:208 [inline]
BUG: KMSAN: uninit-value in usbnet_probe+0x2e57/0x4390 drivers/net/usb/usbnet.c:1830
is_valid_ether_addr include/linux/etherdevice.h:208 [inline]
usbnet_probe+0x2e57/0x4390 drivers/net/usb/usbnet.c:1830
usb_probe_interface+0xd01/0x1310 drivers/usb/core/driver.c:396
call_driver_probe drivers/base/dd.c:-1 [inline]
really_probe+0x4d1/0xd90 drivers/base/dd.c:658
__driver_probe_device+0x268/0x380 drivers/base/dd.c:800
...

Uninit was stored to memory at:
dev_addr_mod+0xb0/0x550 net/core/dev_addr_lists.c:582
__dev_addr_set include/linux/netdevice.h:4874 [inline]
eth_hw_addr_set include/linux/etherdevice.h:325 [inline]
aqc111_bind+0x35f/0x1150 drivers/net/usb/aqc111.c:717
usbnet_probe+0xbe6/0x4390 drivers/net/usb/usbnet.c:1772
usb_probe_interface+0xd01/0x1310 drivers/usb/core/driver.c:396
...

Uninit was stored to memory at:
ether_addr_copy include/linux/etherdevice.h:305 [inline]
aqc111_read_perm_mac drivers/net/usb/aqc111.c:663 [inline]
aqc111_bind+0x794/0x1150 drivers/net/usb/aqc111.c:713
usbnet_probe+0xbe6/0x4390 drivers/net/usb/usbnet.c:1772
usb_probe_interface+0xd01/0x1310 drivers/usb/core/driver.c:396
call_driver_probe drivers/base/dd.c:-1 [inline]
...

Local variable buf.i created at:
aqc111_read_perm_mac drivers/net/usb/aqc111.c:656 [inline]
aqc111_bind+0x221/0x1150 drivers/net/usb/aqc111.c:713
usbnet_probe+0xbe6/0x4390 drivers/net/usb/usbnet.c:1772

Reported-by: syzbot+3b6b9ff7b80430020c7b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3b6b9ff7b80430020c7b
Tested-by: syzbot+3b6b9ff7b80430020c7b@syzkaller.appspotmail.com
Fixes: df2d59a2ab6c ("net: usb: aqc111: Add support for getting and setting of MAC address")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@fintech.ru>
Link: https://patch.msgid.link/20250520113240.2369438-1-n.zhandarovich@fintech.ru
Signed-off-by: Paolo Abeni <pabeni@redhat.com>