KASAN: slab-out-of-bounds Read in fib6_rule_suppress

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: a6cdeeb1 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14c3130ea00000
kernel config: https://syzkaller.appspot.com/x/.config?x=f7a0e5816ab80450
dashboard link: https://syzkaller.appspot.com/bug?extid=5a982749cee362170557
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [da...@davemloft.net kuz...@ms2.inr.ac.ru
linux-...@vger.kernel.org net...@vger.kernel.org yosh...@linux-ipv6.org
net...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+5a9827...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in fib6_rule_suppress+0x25a/0x270
net/ipv6/fib6_rules.c:273
Read of size 8 at addr ffff888084539ae8 by task ksoftirqd/1/16

CPU: 1 PID: 16 Comm: ksoftirqd/1 Not tainted 5.2.0-rc3+ #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
__kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
kasan_report+0x12/0x20 mm/kasan/common.c:614
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
fib6_rule_suppress+0x25a/0x270 net/ipv6/fib6_rules.c:273
fib_rules_lookup+0x81d/0xa90 net/core/fib_rules.c:306
fib6_rule_lookup+0x384/0x5a0 net/ipv6/fib6_rules.c:108
ip6_route_input_lookup+0xb7/0xd0 net/ipv6/route.c:2082
ip6_route_input+0x5e2/0x9e0 net/ipv6/route.c:2217
ip6_rcv_finish_core.isra.0+0x174/0x590 net/ipv6/ip6_input.c:63
ip6_rcv_finish+0x17a/0x310 net/ipv6/ip6_input.c:74
NF_HOOK include/linux/netfilter.h:305 [inline]
NF_HOOK include/linux/netfilter.h:299 [inline]
ipv6_rcv+0x10e/0x420 net/ipv6/ip6_input.c:272
__netif_receive_skb_one_core+0x113/0x1a0 net/core/dev.c:4981
__netif_receive_skb+0x2c/0x1d0 net/core/dev.c:5095
process_backlog+0x206/0x750 net/core/dev.c:5906
napi_poll net/core/dev.c:6329 [inline]
net_rx_action+0x4f5/0x1070 net/core/dev.c:6395
__do_softirq+0x25c/0x94c kernel/softirq.c:293
run_ksoftirqd kernel/softirq.c:604 [inline]
run_ksoftirqd+0x8e/0x110 kernel/softirq.c:596
smpboot_thread_fn+0x6a3/0xa30 kernel/smpboot.c:165
kthread+0x354/0x420 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 8503:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_kmalloc mm/kasan/common.c:489 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:497
slab_post_alloc_hook mm/slab.h:437 [inline]
slab_alloc mm/slab.c:3326 [inline]
kmem_cache_alloc+0x11a/0x6f0 mm/slab.c:3488
dst_alloc+0x10e/0x200 net/core/dst.c:93
ip6_dst_alloc+0x34/0xa0 net/ipv6/route.c:352
ip6_rt_pcpu_alloc net/ipv6/route.c:1281 [inline]
rt6_make_pcpu_route net/ipv6/route.c:1310 [inline]
ip6_pol_route+0x596/0xf40 net/ipv6/route.c:2054
ip6_pol_route_input+0x65/0x80 net/ipv6/route.c:2070
fib6_rule_lookup+0x133/0x5a0 net/ipv6/fib6_rules.c:116
ip6_route_input_lookup+0xb7/0xd0 net/ipv6/route.c:2082
ip6_route_input+0x5e2/0x9e0 net/ipv6/route.c:2217
ip6_rcv_finish_core.isra.0+0x174/0x590 net/ipv6/ip6_input.c:63
ip6_rcv_finish+0x17a/0x310 net/ipv6/ip6_input.c:74
NF_HOOK include/linux/netfilter.h:305 [inline]
NF_HOOK include/linux/netfilter.h:299 [inline]
ipv6_rcv+0x10e/0x420 net/ipv6/ip6_input.c:272
__netif_receive_skb_one_core+0x113/0x1a0 net/core/dev.c:4981
__netif_receive_skb+0x2c/0x1d0 net/core/dev.c:5095
process_backlog+0x206/0x750 net/core/dev.c:5906
napi_poll net/core/dev.c:6329 [inline]
net_rx_action+0x4f5/0x1070 net/core/dev.c:6395
__do_softirq+0x25c/0x94c kernel/softirq.c:293

Freed by task 9:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
__cache_free mm/slab.c:3432 [inline]
kmem_cache_free+0x86/0x260 mm/slab.c:3698
dst_destroy+0x29e/0x3c0 net/core/dst.c:129
dst_destroy_rcu+0x16/0x19 net/core/dst.c:142
__rcu_reclaim kernel/rcu/rcu.h:222 [inline]
rcu_do_batch kernel/rcu/tree.c:2092 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2310 [inline]
rcu_core+0xba5/0x1500 kernel/rcu/tree.c:2291
__do_softirq+0x25c/0x94c kernel/softirq.c:293

The buggy address belongs to the object at ffff888084539a00
which belongs to the cache ip6_dst_cache of size 224
The buggy address is located 8 bytes to the right of
224-byte region [ffff888084539a00, ffff888084539ae0)
The buggy address belongs to the page:
page:ffffea0002114e40 refcount:1 mapcount:0 mapping:ffff888216bbb180
index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0002386f88 ffffea000263f708 ffff888216bbb180
raw: 0000000000000000 ffff888084539000 000000010000000c 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888084539980: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
ffff888084539a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff888084539a80: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
^
ffff888084539b00: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
ffff888084539b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.