KASAN: null-ptr-deref Write in build_segment

similar bugs (1):
Kernel	Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
linux-4.14	KASAN: null-ptr-deref Write in build_segment_manager				1	631d	631d	0/1	auto-closed as invalid on 2021/01/31 08:13

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BUG: KASAN: null-ptr-deref in memset include/linux/string.h:361 [inline]
BUG: KASAN: null-ptr-deref in build_sit_entries fs/f2fs/segment.c:3286 [inline]
BUG: KASAN: null-ptr-deref in build_segment_manager+0x44b1/0x80e0 fs/f2fs/segment.c:3567
Write of size 64 at addr           (null) by task syz-executor.0/25825

CPU: 0 PID: 25825 Comm: syz-executor.0 Not tainted 4.14.256-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x281 lib/dump_stack.c:58
 kasan_report_error.cold+0x144/0x191 mm/kasan/report.c:349
 kasan_report+0x6f/0x80 mm/kasan/report.c:409
 memset+0x20/0x40 mm/kasan/kasan.c:285
 memset include/linux/string.h:361 [inline]
 build_sit_entries fs/f2fs/segment.c:3286 [inline]
 build_segment_manager+0x44b1/0x80e0 fs/f2fs/segment.c:3567
 f2fs_fill_super+0x2e21/0x56a0 fs/f2fs/super.c:2581
 mount_bdev+0x2b3/0x360 fs/super.c:1134
 mount_fs+0x92/0x2a0 fs/super.c:1237
 vfs_kern_mount.part.0+0x5b/0x470 fs/namespace.c:1046
 vfs_kern_mount fs/namespace.c:1036 [inline]
 do_new_mount fs/namespace.c:2572 [inline]
 do_mount+0xe65/0x2a10 fs/namespace.c:2902
 SYSC_mount fs/namespace.c:3118 [inline]
 SyS_mount+0xa8/0x120 fs/namespace.c:3095
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7f7a9db2601a
RSP: 002b:00007f7a9ca99fa8 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000020000200 RCX: 00007f7a9db2601a
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f7a9ca9a000
RBP: 00007f7a9ca9a040 R08: 00007f7a9ca9a040 R09: 0000000020000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000020000000
R13: 0000000020000100 R14: 00007f7a9ca9a000 R15: 0000000020014b00
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