==================================================================
BUG: KASAN: use-after-free in rb_first_postorder+0x7c/0xa0 lib/rbtree.c:671
Read of size 8 at addr ffff8801c8f94240 by task syz-executor7/9897

CPU: 1 PID: 9897 Comm: syz-executor7 Not tainted 4.15.0-rc7+ #181
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: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
 rb_first_postorder+0x7c/0xa0 lib/rbtree.c:671
 tipc_group_join+0x120/0x2d0 net/tipc/group.c:210
 tipc_sk_join net/tipc/socket.c:2781 [inline]
 tipc_setsockopt+0x67e/0xcc0 net/tipc/socket.c:2876
 SYSC_setsockopt net/socket.c:1821 [inline]
 SyS_setsockopt+0x189/0x360 net/socket.c:1800
 entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x452ac9
RSP: 002b:00007f75be5b5c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
RDX: 0000000000000087 RSI: 000000000000010f RDI: 0000000000000014
RBP: 00000000000003aa R08: 0000000000000010 R09: 0000000000000000
R10: 00000000207f0000 R11: 0000000000000212 R12: 00000000006f3890
R13: 00000000ffffffff R14: 00007f75be5b66d4 R15: 0000000000000000

Allocated by task 9897:
 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
 kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3610
 kmalloc include/linux/slab.h:499 [inline]
 kzalloc include/linux/slab.h:688 [inline]
 tipc_group_create+0x144/0x900 net/tipc/group.c:180
 tipc_sk_join net/tipc/socket.c:2762 [inline]
 tipc_setsockopt+0x274/0xcc0 net/tipc/socket.c:2876
 SYSC_setsockopt net/socket.c:1821 [inline]
 SyS_setsockopt+0x189/0x360 net/socket.c:1800
 entry_SYSCALL_64_fastpath+0x23/0x9a

Freed by task 9897:
 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:3488 [inline]
 kfree+0xd6/0x260 mm/slab.c:3803
 tipc_group_delete+0x2c8/0x3d0 net/tipc/group.c:234
 tipc_sk_join net/tipc/socket.c:2775 [inline]
 tipc_setsockopt+0xba3/0xcc0 net/tipc/socket.c:2876
 SYSC_setsockopt net/socket.c:1821 [inline]
 SyS_setsockopt+0x189/0x360 net/socket.c:1800
 entry_SYSCALL_64_fastpath+0x23/0x9a

The buggy address belongs to the object at ffff8801c8f94240
 which belongs to the cache kmalloc-128 of size 128
The buggy address is located 0 bytes inside of
 128-byte region [ffff8801c8f94240, ffff8801c8f942c0)
The buggy address belongs to the page:
page:ffffea000723e500 count:1 mapcount:0 mapping:ffff8801c8f94000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c8f94000 0000000000000000 0000000100000015
raw: ffffea000726bfa0 ffffea00071c1220 ffff8801dac00640 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c8f94100: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff8801c8f94180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801c8f94200: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                           ^
 ffff8801c8f94280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff8801c8f94300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================