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BUG: KASAN: use-after-free in memset include/linux/string.h:337 [inline]
BUG: KASAN: use-after-free in __ext4_expand_extra_isize+0x16f/0x240 fs/ext4/inode.c:5897
Write of size 4063 at addr ffff8881978b31a0 by task syz-executor2/6028

CPU: 0 PID: 6028 Comm: syz-executor2 Not tainted 4.20.0-rc6+ #373
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
 print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.8+0x242/0x309 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
 memset+0x23/0x40 mm/kasan/kasan.c:285
 memset include/linux/string.h:337 [inline]
 __ext4_expand_extra_isize+0x16f/0x240 fs/ext4/inode.c:5897
 ext4_try_to_expand_extra_isize fs/ext4/inode.c:5949 [inline]
 ext4_mark_inode_dirty+0x8f9/0xb20 fs/ext4/inode.c:6025
 ext4_dirty_inode+0x97/0xc0 fs/ext4/inode.c:6059
 __mark_inode_dirty+0x7c3/0x1510 fs/fs-writeback.c:2122
 generic_update_time+0x26a/0x450 fs/inode.c:1654
 update_time fs/inode.c:1670 [inline]
 touch_atime+0x29c/0x320 fs/inode.c:1741
 get_link fs/namei.c:1057 [inline]
 trailing_symlink+0x2cb/0x970 fs/namei.c:2263
 path_mountpoint+0x762/0x2180 fs/namei.c:2696
 filename_mountpoint+0x245/0x460 fs/namei.c:2717
 user_path_mountpoint_at+0x37/0x40 fs/namei.c:2747
 ksys_umount+0x1c5/0x12d0 fs/namespace.c:1645
 __do_sys_umount fs/namespace.c:1671 [inline]
 __se_sys_umount fs/namespace.c:1669 [inline]
 __x64_sys_umount+0x54/0x80 fs/namespace.c:1669
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a0a7
Code: 44 00 00 b8 08 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 9d 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 7d 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffd954d3748 EFLAGS: 00000202 ORIG_RAX: 00000000000000a6
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000045a0a7
RDX: 0000000000402eb0 RSI: 0000000000000002 RDI: 00007ffd954d37f0
RBP: 00000000000010c3 R08: 0000000000000000 R09: 0000000000000011
R10: 000000000000000a R11: 0000000000000202 R12: 00007ffd954d4880
R13: 00000000025d2940 R14: 0000000000000000 R15: 0000000000000002

The buggy address belongs to the page:
page:ffffea00065e2cc0 count:2 mapcount:0 mapping:ffff8881cc4bf658 index:0x445
flags: 0x2fffc000000203a(referenced|dirty|lru|active|private)
raw: 02fffc000000203a ffffea0006882808 ffffea0006acd788 ffff8881cc4bf658
raw: 0000000000000445 ffff8881d4826348 00000002ffffffff ffff88818104c380
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff88818104c380

Memory state around the buggy address:
 ffff8881978b3f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8881978b3f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8881978b4000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff8881978b4080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881978b4100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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