KASAN: null-ptr-deref Write in copy

==================================================================
BUG: KASAN: null-ptr-deref in atomic_inc include/asm-generic/atomic-instrumented.h:109 [inline]
BUG: KASAN: null-ptr-deref in get_nsproxy include/linux/nsproxy.h:85 [inline]
BUG: KASAN: null-ptr-deref in copy_namespaces+0x250/0x4d0 kernel/nsproxy.c:147
Write of size 4 at addr 0000000000000000 by task syz-executor3/6111

CPU: 1 PID: 6111 Comm: syz-executor3 Not tainted 4.20.0-rc3+ #311
list_add corruption. next->prev should be prev (ffff8881dae2d798), but was ffffffff89f9e340. (next=ffff88819001a6b0).
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+0x244/0x39d lib/dump_stack.c:113
 kasan_report_error mm/kasan/report.c:352 [inline]
 kasan_report.cold.8+0x6d/0x309 mm/kasan/report.c:412
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
 kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278
 atomic_inc include/asm-generic/atomic-instrumented.h:109 [inline]
 get_nsproxy include/linux/nsproxy.h:85 [inline]
 copy_namespaces+0x250/0x4d0 kernel/nsproxy.c:147
 copy_process+0x4cd5/0x87a0 kernel/fork.c:1920
 _do_fork+0x1cb/0x11d0 kernel/fork.c:2216
 __do_sys_clone kernel/fork.c:2323 [inline]
 __se_sys_clone kernel/fork.c:2317 [inline]
 __x64_sys_clone+0xbf/0x150 kernel/fork.c:2317
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455b1a
Code: f7 d8 64 89 04 25 d4 02 00 00 64 4c 8b 0c 25 10 00 00 00 31 d2 4d 8d 91 d0 02 00 00 31 f6 bf 11 00 20 01 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 f5 00 00 00 85 c0 41 89 c5 0f 85 fc 00 00
RSP: 002b:00007fff520d55c0 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007fff520d55c0 RCX: 0000000000455b1a
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 00007fff520d5600 R08: 0000000000000001 R09: 0000000002453940
R10: 0000000002453c10 R11: 0000000000000246 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000003
==================================================================
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:25!