KMSAN: uninit-value in build_audio_procunit

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    3c8ca708 test_kmsan.c: fix SPDX comment
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=133fb3cf600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c07a3d4f8a59e198
dashboard link: https://syzkaller.appspot.com/bug?extid=85f45d8bd343473faf15
compiler:       clang version 9.0.0 (/home/glider/llvm/clang  
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12201cef600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1281b8ff600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+85f45d8bd343473faf15@xxxxxxxxxxxxxxxxxxxxxxxxx

usb 1-1: New USB device found, idVendor=1d6b, idProduct=0101, bcdDevice=  
0.40
usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1: Product: syz
usb 1-1: Manufacturer: syz
usb 1-1: SerialNumber: syz
=====================================================
BUG: KMSAN: uninit-value in build_audio_procunit+0x1be8/0x2490  
sound/usb/mixer.c:2438
CPU: 1 PID: 3381 Comm: kworker/1:2 Not tainted 5.4.0-rc3+ #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+0x191/0x1f0 lib/dump_stack.c:113
 kmsan_report+0x14a/0x2f0 mm/kmsan/kmsan_report.c:110
 __msan_warning+0x73/0xf0 mm/kmsan/kmsan_instr.c:245
 build_audio_procunit+0x1be8/0x2490 sound/usb/mixer.c:2438
 parse_audio_unit+0x115c/0x7490 sound/usb/mixer.c:2483
 snd_usb_mixer_controls sound/usb/mixer.c:3095 [inline]
 snd_usb_create_mixer+0x1d7c/0x4070 sound/usb/mixer.c:3445
 usb_audio_probe+0x286b/0x3eb0 sound/usb/card.c:653
 usb_probe_interface+0xd19/0x1310 drivers/usb/core/driver.c:361
 really_probe+0xd91/0x1f90 drivers/base/dd.c:552
 driver_probe_device+0x1ba/0x510 drivers/base/dd.c:721
 __device_attach_driver+0x5b8/0x790 drivers/base/dd.c:828
 bus_for_each_drv+0x28e/0x3b0 drivers/base/bus.c:430
 __device_attach+0x489/0x750 drivers/base/dd.c:894
 device_initial_probe+0x4a/0x60 drivers/base/dd.c:941
 bus_probe_device+0x131/0x390 drivers/base/bus.c:490
 device_add+0x25b5/0x2df0 drivers/base/core.c:2201
 usb_set_configuration+0x309f/0x3710 drivers/usb/core/message.c:2027
 generic_probe+0xe7/0x280 drivers/usb/core/generic.c:210
 usb_probe_device+0x146/0x200 drivers/usb/core/driver.c:266
 really_probe+0xd91/0x1f90 drivers/base/dd.c:552
 driver_probe_device+0x1ba/0x510 drivers/base/dd.c:721
 __device_attach_driver+0x5b8/0x790 drivers/base/dd.c:828
 bus_for_each_drv+0x28e/0x3b0 drivers/base/bus.c:430
 __device_attach+0x489/0x750 drivers/base/dd.c:894
 device_initial_probe+0x4a/0x60 drivers/base/dd.c:941
 bus_probe_device+0x131/0x390 drivers/base/bus.c:490
 device_add+0x25b5/0x2df0 drivers/base/core.c:2201
 usb_new_device+0x23e5/0x2fb0 drivers/usb/core/hub.c:2536
 hub_port_connect drivers/usb/core/hub.c:5098 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
 port_event drivers/usb/core/hub.c:5359 [inline]
 hub_event+0x581d/0x72f0 drivers/usb/core/hub.c:5441
 process_one_work+0x1572/0x1ef0 kernel/workqueue.c:2269
 worker_thread+0x111b/0x2460 kernel/workqueue.c:2415
 kthread+0x4b5/0x4f0 kernel/kthread.c:256
 ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:355

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:151 [inline]
 kmsan_internal_poison_shadow+0x60/0x110 mm/kmsan/kmsan.c:134
 kmsan_slab_alloc+0xaa/0x130 mm/kmsan/kmsan_hooks.c:88
 slab_alloc_node mm/slub.c:2792 [inline]
 slab_alloc mm/slub.c:2801 [inline]
 __kmalloc+0x28e/0x430 mm/slub.c:3832
 kmalloc include/linux/slab.h:561 [inline]
 usb_get_configuration+0x50d/0x76a0 drivers/usb/core/config.c:857
 usb_enumerate_device drivers/usb/core/hub.c:2369 [inline]
 usb_new_device+0x224/0x2fb0 drivers/usb/core/hub.c:2505
 hub_port_connect drivers/usb/core/hub.c:5098 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
 port_event drivers/usb/core/hub.c:5359 [inline]
 hub_event+0x581d/0x72f0 drivers/usb/core/hub.c:5441
 process_one_work+0x1572/0x1ef0 kernel/workqueue.c:2269
 worker_thread+0x111b/0x2460 kernel/workqueue.c:2415
 kthread+0x4b5/0x4f0 kernel/kthread.c:256
 ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:355
=====================================================


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