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SubjectKASAN: use-after-free Write in __ext4_expand_extra_isize

syzbot hit the following crash on upstream commit
0adb32858b0bddf4ada5f364a84ed60b196dbcda (Sun Apr 1 21:20:27 2018 +0000)
Linux 4.16
syzbot dashboard link:

C reproducer:
syzkaller reproducer:
Raw console output:
Kernel config:
compiler: gcc (GCC) 7.1.1 20170620

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IPVS: ftp: loaded support on port[0] = 21
EXT4-fs (sda1): re-mounted. Opts: debug_want_extra_isize=7632
BUG: KASAN: use-after-free in memset include/linux/string.h:330 [inline]
BUG: KASAN: use-after-free in __ext4_expand_extra_isize+0x157/0x230
Write of size 7600 at addr ffff8801c7ee86a0 by task syzkaller547255/4428

CPU: 0 PID: 4428 Comm: syzkaller547255 Not tainted 4.16.0+ #10
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+0x194/0x24d lib/dump_stack.c:53
print_address_description+0x73/0x250 mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report+0x23c/0x360 mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
memset+0x23/0x40 mm/kasan/kasan.c:285
memset include/linux/string.h:330 [inline]
__ext4_expand_extra_isize+0x157/0x230 fs/ext4/inode.c:5779
ext4_try_to_expand_extra_isize fs/ext4/inode.c:5831 [inline]
ext4_mark_inode_dirty+0x7a9/0xa10 fs/ext4/inode.c:5907
ext4_unlink+0xc6f/0x1100 fs/ext4/namei.c:3038
vfs_unlink+0x283/0x480 fs/namei.c:3978
do_unlinkat+0x731/0x940 fs/namei.c:4041
SYSC_unlink fs/namei.c:4088 [inline]
SyS_unlink+0x26/0x30 fs/namei.c:4086
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
RIP: 0033:0x447b77
RSP: 002b:00007ffc704d9d88 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000447b77
RDX: 00007ffc704d9d90 RSI: 00007ffc704d9d90 RDI: 00007ffc704d9e20
RBP: 00007ffc704db5a0 R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000006 R11: 0000000000000206 R12: 0000000001c648a0
R13: 0000000000000000 R14: 0000000000007384 R15: 00007ffc704daf98

The buggy address belongs to the page:
page:ffffea00071fba00 count:2 mapcount:0 mapping:ffff8801d52ef660
flags: 0x2fffc0000001064(referenced|lru|active|private)
raw: 02fffc0000001064 ffff8801d52ef660 00000000000004a7 00000002ffffffff
raw: ffffea0006e70c20 ffffea0006d9a5a0 ffff8801a99933f0 ffff8801d9a96b40
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801c7ee9f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8801c7ee9f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8801c7eea000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff8801c7eea080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff8801c7eea100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

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