Re: KMSAN: uninit-value in joydev_connect

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    ce8056d1 wip: changed copy_from_user where instrumented
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=127b9fba900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3afe005fb99591f
dashboard link: https://syzkaller.appspot.com/bug?extid=6a1bb5a33a0b128085bc
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1472674e900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15a1339a900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6a1bb5a33a0b128085bc@xxxxxxxxxxxxxxxxxxxxxxxxx

usb 1-1: config 0 interface 219 altsetting 0 endpoint 0xA has invalid wMaxPacketSize 0
usb 1-1: New USB device found, idVendor=078c, idProduct=1002, bcdDevice=e6.47
usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 1-1: config 0 descriptor??
gtco 1-1:0.219: Collection level already at zero
input: GTCO_CalComp as /devices/platform/dummy_hcd.0/usb1/1-1/1-1:0.219/input/input5
=====================================================
BUG: KMSAN: uninit-value in joydev_connect+0x10c0/0x1920 drivers/input/joydev.c:958
CPU: 1 PID: 27 Comm: kworker/1:1 Not tainted 5.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: usb_hub_wq hub_event
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x21c/0x280 lib/dump_stack.c:118
 kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
 __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
 joydev_connect+0x10c0/0x1920 drivers/input/joydev.c:958
 input_attach_handler drivers/input/input.c:1031 [inline]
 input_register_device+0x1d7b/0x21c0 drivers/input/input.c:2229
 gtco_probe+0x32ce/0x39b0 drivers/input/tablet/gtco.c:990
 usb_probe_interface+0xece/0x1550 drivers/usb/core/driver.c:374
 really_probe+0xf20/0x20b0 drivers/base/dd.c:529
 driver_probe_device+0x293/0x390 drivers/base/dd.c:701
 __device_attach_driver+0x63f/0x830 drivers/base/dd.c:807
 bus_for_each_drv+0x2ca/0x3f0 drivers/base/bus.c:431
 __device_attach+0x4e2/0x7f0 drivers/base/dd.c:873
 devic