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BUG: KASAN: use-after-free in rt6_mtu_change_route+0x8ea/0x8f0 net/ipv6/route.c:3742
Read of size 8 at addr ffff8801c0ec6480 by task syz-executor6/5192

CPU: 1 PID: 5192 Comm: syz-executor6 Not tainted 4.15.0-rc7+ #188
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
 rt6_mtu_change_route+0x8ea/0x8f0 net/ipv6/route.c:3742
 fib6_clean_node+0x389/0x580 net/ipv6/ip6_fib.c:1912
 fib6_walk_continue+0x46c/0x8a0 net/ipv6/ip6_fib.c:1838
 fib6_walk+0x91/0xf0 net/ipv6/ip6_fib.c:1886
 fib6_clean_tree+0x1e6/0x340 net/ipv6/ip6_fib.c:1963
 __fib6_clean_all+0x1f4/0x3a0 net/ipv6/ip6_fib.c:1979
 fib6_clean_all+0x27/0x30 net/ipv6/ip6_fib.c:1990
 rt6_mtu_change+0xde/0x140 net/ipv6/route.c:3764
 addrconf_notify+0x664/0x2310 net/ipv6/addrconf.c:3394
 notifier_call_chain+0x136/0x2c0 kernel/notifier.c:93
 __raw_notifier_call_chain kernel/notifier.c:394 [inline]
 raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
 call_netdevice_notifiers_info+0x32/0x70 net/core/dev.c:1708
 call_netdevice_notifiers net/core/dev.c:1726 [inline]
 dev_set_mtu+0x3c5/0x720 net/core/dev.c:7025
 dev_ifsioc+0x73c/0x9b0 net/core/dev_ioctl.c:264
 dev_ioctl+0x2d7/0xfb0 net/core/dev_ioctl.c:566
 sock_do_ioctl+0x94/0xb0 net/socket.c:965
 sock_ioctl+0x2c2/0x440 net/socket.c:1055
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x452cf9
RSP: 002b:00007efe20558c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452cf9
RDX: 0000000020001fd8 RSI: 0000000000008922 RDI: 0000000000000013
RBP: 000000000000013b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006efe28
R13: 00000000ffffffff R14: 00007efe205596d4 R15: 0000000000000000

Allocated by task 26832:
 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:3544
 dst_alloc+0x11f/0x1a0 net/core/dst.c:104
 __ip6_dst_alloc+0x35/0x90 net/ipv6/route.c:361
 ip6_dst_alloc+0x29/0xb0 net/ipv6/route.c:376
 ip6_route_info_create+0x4ff/0x2e20 net/ipv6/route.c:2538
 ip6_route_add+0xa2/0x190 net/ipv6/route.c:2779
 ipv6_route_ioctl+0x4db/0x6b0 net/ipv6/route.c:3299
 inet6_ioctl+0xef/0x1e0 net/ipv6/af_inet6.c:520
 sock_do_ioctl+0x65/0xb0 net/socket.c:958
 sock_ioctl+0x2c2/0x440 net/socket.c:1055
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 entry_SYSCALL_64_fastpath+0x23/0x9a

Freed by task 31766:
 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]
 kmem_cache_free+0x83/0x2a0 mm/slab.c:3746
 dst_destroy+0x257/0x370 net/core/dst.c:140
 dst_destroy_rcu+0x16/0x20 net/core/dst.c:153
 __rcu_reclaim kernel/rcu/rcu.h:195 [inline]
 rcu_do_batch kernel/rcu/tree.c:2758 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:3012 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2979 [inline]
 rcu_process_callbacks+0xd6c/0x17f0 kernel/rcu/tree.c:2996
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801c0ec6480
 which belongs to the cache ip6_dst_cache of size 320
The buggy address is located 0 bytes inside of
 320-byte region [ffff8801c0ec6480, ffff8801c0ec65c0)
The buggy address belongs to the page:
page:ffffea000703b180 count:1 mapcount:0 mapping:ffff8801c0ec6000 index:0xffff8801c0ec6c00
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c0ec6000 ffff8801c0ec6c00 0000000100000008
raw: ffffea0007106c60 ffffea000750dce0 ffff8801d3287900 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c0ec6380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801c0ec6400: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>ffff8801c0ec6480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8801c0ec6500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c0ec6580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
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