==================================================================
BUG: KASAN: use-after-free in shm_get_unmapped_area+0xfd/0x120 ipc/shm.c:477
Read of size 8 at addr ffff8801d8d06d28 by task syz-executor0/4272

CPU: 1 PID: 4272 Comm: syz-executor0 Not tainted 4.14.0-rc4-next-20171009+ #33
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:52
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 shm_get_unmapped_area+0xfd/0x120 ipc/shm.c:477
 get_unmapped_area+0x18d/0x300 mm/mmap.c:2101
 do_mmap+0x2aa/0xd50 mm/mmap.c:1364
 do_mmap_pgoff include/linux/mm.h:2180 [inline]
 SYSC_remap_file_pages mm/mmap.c:2830 [inline]
 SyS_remap_file_pages+0x7ce/0xb30 mm/mmap.c:2746
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x4520a9
RSP: 002b:00007f5f40afac08 EFLAGS: 00000216 ORIG_RAX: 00000000000000d8
RAX: ffffffffffffffda RBX: 0000000000718160 RCX: 00000000004520a9
RDX: 0000000000000000 RSI: 0000000000001000 RDI: 0000000020002000
RBP: 0000000000000082 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000216 R12: 00000000004bb652
R13: 00000000ffffffff R14: 0000000000040007 R15: 0000000020001000

Allocated by task 4258:
 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:551
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3562
 kmem_cache_zalloc include/linux/slab.h:687 [inline]
 get_empty_filp+0xfb/0x4f0 fs/file_table.c:123
 alloc_file+0x26/0x3a0 fs/file_table.c:164
 __shmem_file_setup+0x54f/0x6a0 mm/shmem.c:4228
 shmem_kernel_file_setup+0x32/0x40 mm/shmem.c:4254
 newseg+0x7cd/0xcd0 ipc/shm.c:588
 ipcget_new ipc/util.c:310 [inline]
 ipcget+0x8f0/0xfd0 ipc/util.c:648
 SYSC_shmget ipc/shm.c:674 [inline]
 SyS_shmget+0x158/0x230 ipc/shm.c:658
 entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 4241:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3504 [inline]
 kmem_cache_free+0x77/0x280 mm/slab.c:3764
 file_free_rcu+0x5c/0x70 fs/file_table.c:50
 __rcu_reclaim kernel/rcu/rcu.h:195 [inline]
 rcu_do_batch kernel/rcu/tree.c:2691 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2945 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2912 [inline]
 rcu_process_callbacks+0xd74/0x17d0 kernel/rcu/tree.c:2929
 __do_softirq+0x29d/0xbb2 kernel/softirq.c:284

The buggy address belongs to the object at ffff8801d8d06d00
 which belongs to the cache filp of size 488
The buggy address is located 40 bytes inside of
 488-byte region [ffff8801d8d06d00, ffff8801d8d06ee8)
The buggy address belongs to the page:
page:ffffea0007634180 count:1 mapcount:0 mapping:ffff8801d8d06080 index:0x0
flags: 0x200000000000100(slab)
raw: 0200000000000100 ffff8801d8d06080 0000000000000000 0000000100000006
raw: ffffea000764ffa0 ffffea0007634320 ffff8801dae3e300 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d8d06c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc
 ffff8801d8d06c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801d8d06d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff8801d8d06d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d8d06e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================