KMSAN: uninit-value in copy_siginfo_to_user

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    8fc8ecd1c58a kmsan: unpoison regs in arch_uprobe_exception..
git tree:       https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=1758708f800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9fa436d3ae606638
dashboard link: https://syzkaller.appspot.com/bug?extid=ab504332a376ca03331e
compiler:       clang version 7.0.0 (trunk 332596)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=170eeed7800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ab504332a376ca03331e@xxxxxxxxxxxxxxxxxxxxxxxxx

IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KMSAN: uninit-value in copy_siginfo_to_user+0x383/0x1270  
kernel/signal.c:2870
CPU: 1 PID: 4746 Comm: syz-executor0 Not tainted 4.17.0-rc5+ #103
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+0x185/0x1d0 lib/dump_stack.c:113
 kmsan_report+0x149/0x260 mm/kmsan/kmsan.c:1084
 __msan_warning_32+0x6e/0xc0 mm/kmsan/kmsan_instr.c:686
 copy_siginfo_to_user+0x383/0x1270 kernel/signal.c:2870
 ptrace_peek_siginfo kernel/ptrace.c:741 [inline]
 ptrace_request+0x1d6a/0x20e0 kernel/ptrace.c:912
 arch_ptrace+0x1f6/0x1230 arch/x86/kernel/ptrace.c:877
 __do_sys_ptrace kernel/ptrace.c:1145 [inline]
 __se_sys_ptrace+0x309/0x850 kernel/ptrace.c:1110
 __x64_sys_ptrace+0x11e/0x170 kernel/ptrace.c:1110
 do_syscall_64+0x152/0x230 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x455a09
RSP: 002b:00007ffc971089c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000065
RAX: ffffffffffffffda RBX: 0000000000acf914 RCX: 0000000000455a09
RDX: 0000000000730004 RSI: 0000000000000001 RDI: 0000000000004209
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000558 R14: 00000000006fd0e0 R15: 000000000000b0fe

Local variable description: ----kiov@ptrace_request
Variable was created at:
 ptrace_request+0x194/0x20e0 kernel/ptrace.c:885
 arch_ptrace+0x1f6/0x1230 arch/x86/kernel/ptrace.c:877
==================================================================


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