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BUG: KASAN: use-after-free in filemap_fault+0x25f5/0x2a00 mm/filemap.c:2559
Read of size 8 at addr ffff88809f4d45a8 by task syz-executor4/12040

CPU: 0 PID: 12040 Comm: syz-executor4 Not tainted 4.20.0-next-20190107 #6
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+0x1db/0x2d0 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
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
 filemap_fault+0x25f5/0x2a00 mm/filemap.c:2559
 ext4_filemap_fault+0x83/0xaf fs/ext4/inode.c:6327
 __do_fault+0x176/0x7b0 mm/memory.c:3013
 do_shared_fault mm/memory.c:3479 [inline]
 do_fault mm/memory.c:3554 [inline]
 handle_pte_fault mm/memory.c:3781 [inline]
 __handle_mm_fault+0x3500/0x55a0 mm/memory.c:3905
 handle_mm_fault+0x4ec/0xc80 mm/memory.c:3942
 do_user_addr_fault arch/x86/mm/fault.c:1475 [inline]
 __do_page_fault+0x5da/0xd60 arch/x86/mm/fault.c:1541
 do_page_fault+0xe6/0x7d8 arch/x86/mm/fault.c:1572
 page_fault+0x1e/0x30 arch/x86/entry/entry_64.S:1143
RIP: 0033:0x43f1f9
Code: b7 0e 66 89 0f 48 83 c6 02 48 83 c7 02 0f 1f 40 00 f6 c2 04 74 0c 8b 0e 89 0f 48 83 c6 04 48 83 c7 04 f6 c2 08 74 0e 48 8b 0e <48> 89 0f 48 83 c6 08 48 83 c7 08 81 e2 f0 00 00 00 74 1f 0f 1f 40
RSP: 002b:00007fff846eaad8 EFLAGS: 00010202
RAX: 0000000020008ff8 RBX: 0000000000000005 RCX: 0031656c69662f2e
RDX: 0000000000000008 RSI: 0000000000740348 RDI: 0000000020008ff8
RBP: 000000000073c040 R08: 0000000000740328 R09: 0000000000000000
R10: 00007fff846eab90 R11: 0000000000000246 R12: 0000000000000003
R13: fffffffffffffffe R14: 000000000073c04c R15: 000000000073c04c

Allocated by task 12041:
 save_stack+0x45/0xd0 mm/kasan/common.c:73
 set_track mm/kasan/common.c:85 [inline]
 kasan_kmalloc mm/kasan/common.c:482 [inline]
 kasan_kmalloc+0xcf/0xe0 mm/kasan/common.c:455
 kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:397
 kmem_cache_alloc+0x12d/0x710 mm/slab.c:3541
 vm_area_alloc+0x7a/0x1d0 kernel/fork.c:331
 mmap_region+0x93b/0x1ca0 mm/mmap.c:1756
 do_mmap+0xa09/0x1220 mm/mmap.c:1559
 do_mmap_pgoff include/linux/mm.h:2421 [inline]
 vm_mmap_pgoff+0x20b/0x2b0 mm/util.c:350
 ksys_mmap_pgoff+0x4f8/0x650 mm/mmap.c:1609
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
 __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
 do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 12042:
 save_stack+0x45/0xd0 mm/kasan/common.c:73
 set_track mm/kasan/common.c:85 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:444
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:452
 __cache_free mm/slab.c:3485 [inline]
 kmem_cache_free+0x86/0x260 mm/slab.c:3747
 vm_area_free+0x1d/0x30 kernel/fork.c:350
 remove_vma+0x142/0x180 mm/mmap.c:185
 remove_vma_list mm/mmap.c:2585 [inline]
 __do_munmap+0x72e/0xef0 mm/mmap.c:2828
 do_munmap mm/mmap.c:2836 [inline]
 mmap_region+0x698/0x1ca0 mm/mmap.c:1729
 do_mmap+0xa09/0x1220 mm/mmap.c:1559
 do_mmap_pgoff include/linux/mm.h:2421 [inline]
 vm_mmap_pgoff+0x20b/0x2b0 mm/util.c:350
 ksys_mmap_pgoff+0x4f8/0x650 mm/mmap.c:1609
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
 __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
 do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88809f4d4568
 which belongs to the cache vm_area_struct(81:syz4) of size 200
The buggy address is located 64 bytes inside of
 200-byte region [ffff88809f4d4568, ffff88809f4d4630)
The buggy address belongs to the page:
page:ffffea00027d3500 count:1 mapcount:0 mapping:ffff88808d26bb40 index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea00027df488 ffffea00023e06c8 ffff88808d26bb40
raw: 0000000000000000 ffff88809f4d4040 000000010000000f ffff8880a494a1c0
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8880a494a1c0

Memory state around the buggy address:
 ffff88809f4d4480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809f4d4500: fb fb fb fb fb fc fc fc fc fc fc fc fc fb fb fb
>ffff88809f4d4580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff88809f4d4600: fb fb fb fb fb fb fc fc fc fc fc fc fc fc 00 00
 ffff88809f4d4680: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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