KMSAN: uninit-value in bcmp

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    d062d017 usb-fuzzer: main usb gadget fuzzer driver
git tree:       kmsan
console output: https://syzkaller.appspot.com/x/log.txt?x=119daa0ca00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=67ebf8b3cce62ce7
dashboard link: https://syzkaller.appspot.com/bug?extid=d8b02c920ae8f3e0be75
compiler:       clang version 9.0.0 (/home/glider/llvm/clang  
06d00afa61eef8f7f501ebdb4e8612ea43ec2d78)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14973970a00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1349a4e2a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+d8b02c920ae8f3e0be75@xxxxxxxxxxxxxxxxxxxxxxxxx

IPVS: ftp: loaded support on port[0] = 21
==================================================================
BUG: KMSAN: uninit-value in memcmp lib/string.c:865 [inline]
BUG: KMSAN: uninit-value in bcmp+0x117/0x180 lib/string.c:887
CPU: 1 PID: 10480 Comm: syz-executor472 Not tainted 5.1.0-rc7+ #5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x191/0x1f0 lib/dump_stack.c:113
 kmsan_report+0x130/0x2a0 mm/kmsan/kmsan.c:619
 __msan_warning+0x75/0xe0 mm/kmsan/kmsan_instr.c:310
 memcmp lib/string.c:865 [inline]
 bcmp+0x117/0x180 lib/string.c:887
 __hw_addr_del_ex net/core/dev_addr_lists.c:123 [inline]
 __dev_mc_del+0x16c/0x690 net/core/dev_addr_lists.c:810
 dev_mc_del+0x6d/0x80 net/core/dev_addr_lists.c:828
 ip_mc_filter_del net/ipv4/igmp.c:1142 [inline]
 __igmp_group_dropped+0x260/0x1320 net/ipv4/igmp.c:1276
 igmp_group_dropped net/ipv4/igmp.c:1306 [inline]
 ip_mc_down+0x1e7/0x3b0 net/ipv4/igmp.c:1714
 inetdev_event+0x22d/0x1df0 net/ipv4/devinet.c:1534
 notifier_call_chain kernel/notifier.c:93 [inline]
 __raw_notifier_call_chain kernel/notifier.c:394 [inline]
 raw_notifier_call_chain+0x13d/0x240 kernel/notifier.c:401
 call_netdevice_notifiers_info net/core/dev.c:1753 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:1765 [inline]
 call_netdevice_notifiers net/core/dev.c:1779 [inline]
 dev_close_many+0x60d/0x9e0 net/core/dev.c:1522
 rollback_registered_many+0x94a/0x2210 net/core/dev.c:8177
 rollback_registered net/core/dev.c:8242 [inline]
 unregister_netdevice_queue+0x593/0xab0 net/core/dev.c:9289
 unregister_netdevice include/linux/netdevice.h:2658 [inline]
 __tun_detach+0x21be/0x2b10 drivers/net/tun.c:727
 tun_detach drivers/net/tun.c:744 [inline]
 tun_chr_close+0xda/0x1c0 drivers/net/tun.c:3443
 __fput+0x4d1/0xbc0 fs/file_table.c:278
 ____fput+0x37/0x40 fs/file_table.c:309
 task_work_run+0x22e/0x2a0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:166 [inline]
 prepare_exit_to_usermode+0x31d/0x420 arch/x86/entry/common.c:197
 syscall_return_slowpath+0x90/0x5c0 arch/x86/entry/common.c:268
 do_syscall_64+0xe2/0xf0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x400f00
Code: 01 f0 ff ff 0f 83 20 0c 00 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f  
44 00 00 83 3d cd 17 2d 00 00 75 14 b8 03 00 00 00 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 f4 0b 00 00 c3 48 83 ec 08 e8 5a 01 00 00
RSP: 002b:00007fff995e0ec8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000005 RCX: 0000000000400f00
RDX: 0000000020000c40 RSI: 0000000000008914 RDI: 0000000000000004
RBP: 00000000004a2470 R08: 0000000000000100 R09: 0000000000000100
R10: 0000000000000100 R11: 0000000000000246 R12: 0000000000401f80
R13: 0000000000402010 R14: 0000000000000000 R15: 0000000000000000

Local variable description: ----buf.i@__igmp_group_dropped
Variable was created at:
 ip_mc_filter_del net/ipv4/igmp.c:1139 [inline]
 __igmp_group_dropped+0x170/0x1320 net/ipv4/igmp.c:1276
 igmp_group_dropped net/ipv4/igmp.c:1306 [inline]
 ip_mc_down+0x1e7/0x3b0 net/ipv4/igmp.c:1714
==================================================================


---
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