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BUG: KASAN: use-after-free in memset include/linux/string.h:389 [inline]
BUG: KASAN: use-after-free in __ext4_expand_extra_isize+0x1ab/0x290 fs/ext4/inode.c:5921
Write of size 4064 at addr ffff88805b2e47a0 by task syz-executor.3/31387

CPU: 0 PID: 31387 Comm: syz-executor.3 Not tainted 5.3.0-next-20190920 #0
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.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
 __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
 kasan_report+0x12/0x20 mm/kasan/common.c:634
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
 memset+0x24/0x40 mm/kasan/common.c:105
 memset include/linux/string.h:389 [inline]
 __ext4_expand_extra_isize+0x1ab/0x290 fs/ext4/inode.c:5921
 ext4_try_to_expand_extra_isize fs/ext4/inode.c:5973 [inline]
 ext4_mark_inode_dirty+0x74e/0x9b0 fs/ext4/inode.c:6049
 ext4_dirty_inode+0x8f/0xc0 fs/ext4/inode.c:6083
 __mark_inode_dirty+0x68e/0x1390 fs/fs-writeback.c:2250
 generic_update_time+0x21c/0x370 fs/inode.c:1667
 update_time fs/inode.c:1683 [inline]
 touch_atime+0x23c/0x2a0 fs/inode.c:1754
 get_link fs/namei.c:1049 [inline]
 trailing_symlink+0x2e3/0x990 fs/namei.c:2253
 path_mountpoint+0x865/0x1e60 fs/namei.c:2686
 filename_mountpoint+0x18e/0x390 fs/namei.c:2707
 user_path_mountpoint_at+0x3a/0x50 fs/namei.c:2737
 ksys_umount+0x164/0xf00 fs/namespace.c:1683
 __do_sys_umount fs/namespace.c:1709 [inline]
 __se_sys_umount fs/namespace.c:1707 [inline]
 __x64_sys_umount+0x54/0x80 fs/namespace.c:1707
 do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c437
Code: 64 89 04 25 d0 02 00 00 58 5f ff d0 48 89 c7 e8 2f be ff ff 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 9d 8d fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffafd58bf8 EFLAGS: 00000206 ORIG_RAX: 00000000000000a6
RAX: ffffffffffffffda RBX: 0000000000000057 RCX: 000000000045c437
RDX: 0000000000403520 RSI: 0000000000000002 RDI: 00007fffafd58ca0
RBP: 00000000000000db R08: 0000000000000000 R09: 000000000000000f
R10: 000000000000000a R11: 0000000000000206 R12: 00007fffafd59d30
R13: 0000555555d7e940 R14: 0000000000000000 R15: 00007fffafd59d30

The buggy address belongs to the page:
page:ffffea00016cb900 refcount:2 mapcount:0 mapping:ffff888219f2f520 index:0x42e
def_blk_aops 
flags: 0x1fffc000000203a(referenced|dirty|lru|active|private)
raw: 01fffc000000203a ffffea00022001c8 ffffea00014ae8c8 ffff888219f2f520
raw: 000000000000042e ffff8880aa056690 00000002ffffffff ffff888059b30000
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff888059b30000

Memory state around the buggy address:
 ffff88805b2e4f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88805b2e4f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88805b2e5000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff88805b2e5080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88805b2e5100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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