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BUG: KASAN: use-after-free in __ext4_check_dir_entry+0x2de/0x320 fs/ext4/dir.c:69
Read of size 2 at addr ffff8801ca683003 by task syz-executor0/20624

CPU: 0 PID: 20624 Comm: syz-executor0 Not tainted 4.16.0+ #12
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+0x1a7/0x27d 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
 __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:431
 __ext4_check_dir_entry+0x2de/0x320 fs/ext4/dir.c:69
 ext4_readdir+0xd34/0x3660 fs/ext4/dir.c:237
 iterate_dir+0x1ca/0x530 fs/readdir.c:51
 ksys_getdents64+0x20d/0x400 fs/readdir.c:314
 SYSC_getdents64 fs/readdir.c:333 [inline]
 SyS_getdents64+0x24/0x30 fs/readdir.c:330
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4552d9
RSP: 002b:00007f56e582cc68 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007f56e582d6d4 RCX: 00000000004552d9
RDX: 00000000000000bc RSI: 0000000020001540 RDI: 0000000000000013
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000000a9 R14: 00000000006f4078 R15: 0000000000000000

Allocated by task 4539:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 slab_post_alloc_hook mm/slab.h:443 [inline]
 slab_alloc mm/slab.c:3380 [inline]
 kmem_cache_alloc+0x11b/0x760 mm/slab.c:3540
 dup_mmap kernel/fork.c:451 [inline]
 dup_mm kernel/fork.c:1233 [inline]
 copy_mm kernel/fork.c:1287 [inline]
 copy_process.part.38+0x4ee7/0x6140 kernel/fork.c:1793
 copy_process kernel/fork.c:1606 [inline]
 _do_fork+0x1f7/0xfa0 kernel/fork.c:2087
 SYSC_clone kernel/fork.c:2194 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2188
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 20048:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
 __cache_free mm/slab.c:3486 [inline]
 kmem_cache_free+0x83/0x2a0 mm/slab.c:3744
 remove_vma+0x162/0x1b0 mm/mmap.c:176
 exit_mmap+0x311/0x500 mm/mmap.c:3056
 __mmput kernel/fork.c:960 [inline]
 mmput+0x23d/0x700 kernel/fork.c:981
 exit_mm kernel/exit.c:544 [inline]
 do_exit+0x9c5/0x2700 kernel/exit.c:852
 do_group_exit+0x149/0x400 kernel/exit.c:968
 get_signal+0x74c/0x16e0 kernel/signal.c:2469
 do_signal+0x90/0x1e90 arch/x86/kernel/signal.c:810
 exit_to_usermode_loop+0x258/0x2f0 arch/x86/entry/common.c:162
 prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:265 [inline]
 do_syscall_64+0x6ec/0x940 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8801ca683000
 which belongs to the cache vm_area_struct(129:syz7) of size 200
The buggy address is located 3 bytes inside of
 200-byte region [ffff8801ca683000, ffff8801ca6830c8)
The buggy address belongs to the page:
page:ffffea000729a0c0 count:1 mapcount:0 mapping:ffff8801ca683000 index:0xffff8801ca683d20
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801ca683000 ffff8801ca683d20 000000010000000c
raw: ffffea0007296ae0 ffffea0006b65a20 ffff8801b1ef3500 ffff8801d8cd8480
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8801d8cd8480

Memory state around the buggy address:
 ffff8801ca682f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801ca682f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8801ca683000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8801ca683080: fb fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc
 ffff8801ca683100: fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb fb
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