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BUG: KASAN: use-after-free in shm_get_unmapped_area+0xfd/0x120 ipc/shm.c:478
Read of size 8 at addr ffff8801be716ce8 by task syz-executor1/5171

CPU: 0 PID: 5171 Comm: syz-executor1 Not tainted 4.15.0-rc8-next-20180119+ #102
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+0x194/0x257 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+0x23b/0x360 mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 shm_get_unmapped_area+0xfd/0x120 ipc/shm.c:478
 get_unmapped_area+0x18d/0x300 mm/mmap.c:2126
 do_mmap+0x27f/0xf70 mm/mmap.c:1368
 do_mmap_pgoff include/linux/mm.h:2224 [inline]
 SYSC_remap_file_pages mm/mmap.c:2857 [inline]
 SyS_remap_file_pages+0x7ce/0xb30 mm/mmap.c:2773
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x452ee9
RSP: 002b:00007fa616697c58 EFLAGS: 00000212 ORIG_RAX: 00000000000000d8
RAX: ffffffffffffffda RBX: 000000000071bf58 RCX: 0000000000452ee9
RDX: 0000000000000000 RSI: 0000000000001000 RDI: 0000000020002000
RBP: 000000000000031d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f3b58
R13: 00000000ffffffff R14: 00007fa6166986d4 R15: 0000000000000005

Allocated by task 5162:
 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
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3541
 kmem_cache_zalloc include/linux/slab.h:691 [inline]
 get_empty_filp+0xfb/0x4f0 fs/file_table.c:122
 alloc_file+0x26/0x390 fs/file_table.c:163
 __shmem_file_setup+0x54f/0x6a0 mm/shmem.c:4230
 shmem_kernel_file_setup+0x32/0x40 mm/shmem.c:4256
 newseg+0x7bd/0xcb0 ipc/shm.c:589
 ipcget_new ipc/util.c:314 [inline]
 ipcget+0x8f0/0xfd0 ipc/util.c:652
 SYSC_shmget ipc/shm.c:675 [inline]
 SyS_shmget+0x158/0x230 ipc/shm.c:659
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 7:
 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:3485 [inline]
 kmem_cache_free+0x86/0x2b0 mm/slab.c:3743
 file_free_rcu+0x5c/0x70 fs/file_table.c:49
 __rcu_reclaim kernel/rcu/rcu.h:172 [inline]
 rcu_do_batch kernel/rcu/tree.c:2674 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2933 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2900 [inline]
 rcu_process_callbacks+0xd6c/0x17f0 kernel/rcu/tree.c:2917
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801be716cc0
 which belongs to the cache filp of size 456
The buggy address is located 40 bytes inside of
 456-byte region [ffff8801be716cc0, ffff8801be716e88)
The buggy address belongs to the page:
page:ffffea0006f9c580 count:1 mapcount:0 mapping:ffff8801be716040 index:0xffff8801be716040
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801be716040 ffff8801be716040 0000000100000005
raw: ffffea00071c77a0 ffffea0006faf920 ffff8801dae2a180 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801be716b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801be716c00: fb fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801be716c80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                          ^
 ffff8801be716d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801be716d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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