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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+0x16c/0x240 fs/ext4/inode.c:5921
Write of size 3869 at addr ffff888041be5883 by task syz-executor2/20496

CPU: 1 PID: 20496 Comm: syz-executor2 Not tainted 5.0.0-rc5-next-20190207 #30
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+0x172/0x1f0 lib/dump_stack.c:113
 print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
 kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x123/0x190 mm/kasan/generic.c:191
 memset+0x24/0x40 mm/kasan/common.c:115
 memset include/linux/string.h:337 [inline]
 __ext4_expand_extra_isize+0x16c/0x240 fs/ext4/inode.c:5921
 ext4_try_to_expand_extra_isize fs/ext4/inode.c:5973 [inline]
 ext4_mark_inode_dirty+0x6e9/0x940 fs/ext4/inode.c:6049
 ext4_rmdir fs/ext4/namei.c:2976 [inline]
 ext4_rmdir+0x9bd/0xc90 fs/ext4/namei.c:2909
 vfs_rmdir fs/namei.c:3880 [inline]
 vfs_rmdir+0x19c/0x470 fs/namei.c:3859
 do_rmdir+0x39e/0x420 fs/namei.c:3941
 __do_sys_rmdir fs/namei.c:3959 [inline]
 __se_sys_rmdir fs/namei.c:3957 [inline]
 __x64_sys_rmdir+0x36/0x40 fs/namei.c:3957
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457ba7
Code: 00 66 90 b8 57 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 2d bb fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 54 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 0d bb fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffcff1a22c8 EFLAGS: 00000207 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 0000000000000065 RCX: 0000000000457ba7
RDX: 0000000000000000 RSI: 0000000000710698 RDI: 00007ffcff1a3400
RBP: 0000000000000005 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000005 R11: 0000000000000207 R12: 00007ffcff1a3400
R13: 0000000001f6c940 R14: 0000000000000000 R15: 0000000000000002

The buggy address belongs to the page:
page:ffffea000106f940 count:2 mapcount:0 mapping:ffff888062074b18 index:0x44a
def_blk_aops 
flags: 0x1fffc000000203a(referenced|dirty|lru|active|private)
raw: 01fffc000000203a ffffea0000aaf008 ffffea000252c248 ffff888062074b18
raw: 000000000000044a ffff8880474ee498 00000002ffffffff ffff88802b0ac6c0
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff88802b0ac6c0

Memory state around the buggy address:
 ffff888041be5f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888041be5f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888041be6000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff888041be6080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888041be6100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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