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BUG: KASAN: use-after-free in tipc_group_size+0x40/0x50 net/tipc/group.c:159
Read of size 2 at addr ffff8801cfb99780 by task syz-executor6/7641

CPU: 0 PID: 7641 Comm: syz-executor6 Not tainted 4.15.0-rc6-next-20180108+ #90
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+0x137/0x198 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_load2_noabort+0x14/0x20 mm/kasan/report.c:431
 tipc_group_size+0x40/0x50 net/tipc/group.c:159
 tipc_poll+0x2bc/0x400 net/tipc/socket.c:739
 sock_poll+0xf9/0x220 net/socket.c:1109
 do_pollfd fs/select.c:826 [inline]
 do_poll fs/select.c:877 [inline]
 do_sys_poll+0x540/0xc80 fs/select.c:971
 SYSC_poll fs/select.c:1029 [inline]
 SyS_poll+0x10d/0x3e0 fs/select.c:1017
 entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x452ac9
RSP: 002b:00007fe931bf3c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000007
RAX: ffffffffffffffda RBX: 000000000071bf58 RCX: 0000000000452ac9
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000020fa2ff8
RBP: 0000000000000567 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f6248
R13: 00000000ffffffff R14: 00007fe931bf46d4 R15: 0000000000000002

Allocated by task 7636:
 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
 kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3607
 kmalloc include/linux/slab.h:515 [inline]
 kzalloc include/linux/slab.h:704 [inline]
 tipc_group_create+0x84/0x7d0 net/tipc/group.c:168
 tipc_sk_join net/tipc/socket.c:2745 [inline]
 tipc_setsockopt+0x201/0x9d0 net/tipc/socket.c:2859
 SYSC_setsockopt net/socket.c:1821 [inline]
 SyS_setsockopt+0x158/0x240 net/socket.c:1800
 entry_SYSCALL_64_fastpath+0x23/0x9a

Freed by task 7636:
 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]
 kfree+0xd9/0x260 mm/slab.c:3800
 tipc_group_delete+0x21d/0x300 net/tipc/group.c:207
 tipc_sk_join net/tipc/socket.c:2758 [inline]
 tipc_setsockopt+0x8df/0x9d0 net/tipc/socket.c:2859
 SYSC_setsockopt net/socket.c:1821 [inline]
 SyS_setsockopt+0x158/0x240 net/socket.c:1800
 entry_SYSCALL_64_fastpath+0x23/0x9a

The buggy address belongs to the object at ffff8801cfb99700
 which belongs to the cache kmalloc-192 of size 192
The buggy address is located 128 bytes inside of
 192-byte region [ffff8801cfb99700, ffff8801cfb997c0)
The buggy address belongs to the page:
page:ffffea00073ee640 count:1 mapcount:0 mapping:ffff8801cfb99000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801cfb99000 0000000000000000 0000000100000010
raw: ffffea000737d620 ffffea0007398ee0 ffff8801db000040 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801cfb99680: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff8801cfb99700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801cfb99780: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                   ^
 ffff8801cfb99800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801cfb99880: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
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