Some elusive syzbot reports are hinting to fib6_info_release(),
with a potential dangling f6i->gc_link anchor.

Add debug checks so that syzbot can catch the issue earlier eventually.

BUG: KASAN: slab-use-after-free in __hlist_del include/linux/list.h:990 [inline]
BUG: KASAN: slab-use-after-free in hlist_del_init include/linux/list.h:1016 [inline]
BUG: KASAN: slab-use-after-free in fib6_clean_expires_locked include/net/ip6_fib.h:533 [inline]
BUG: KASAN: slab-use-after-free in fib6_purge_rt+0x986/0x9c0 net/ipv6/ip6_fib.c:1064
Write of size 8 at addr ffff88802805a840 by task syz-executor.1/10057

CPU: 1 PID: 10057 Comm: syz-executor.1 Not tainted 6.7.0-rc2-syzkaller-00029-g9b6de136 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xc4/0x620 mm/kasan/report.c:475
kasan_report+0xda/0x110 mm/kasan/report.c:588
__hlist_del include/linux/list.h:990 [inline]
hlist_del_init include/linux/list.h:1016 [inline]
fib6_clean_expires_locked include/net/ip6_fib.h:533 [inline]
fib6_purge_rt+0x986/0x9c0 net/ipv6/ip6_fib.c:1064
fib6_del_route net/ipv6/ip6_fib.c:1993 [inline]
fib6_del+0xa7a/0x1750 net/ipv6/ip6_fib.c:2038
__ip6_del_rt net/ipv6/route.c:3866 [inline]
ip6_del_rt+0xf7/0x200 net/ipv6/route.c:3881
ndisc_router_discovery+0x295b/0x3560 net/ipv6/ndisc.c:1372
ndisc_rcv+0x3de/0x5f0 net/ipv6/ndisc.c:1856
icmpv6_rcv+0x1470/0x19c0 net/ipv6/icmp.c:979
ip6_protocol_deliver_rcu+0x170/0x13e0 net/ipv6/ip6_input.c:438
ip6_input_finish+0x14f/0x2f0 net/ipv6/ip6_input.c:483
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ip6_input+0xa1/0xc0 net/ipv6/ip6_input.c:492
ip6_mc_input+0x48b/0xf40 net/ipv6/ip6_input.c:586
dst_input include/net/dst.h:461 [inline]
ip6_rcv_finish net/ipv6/ip6_input.c:79 [inline]
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ipv6_rcv+0x24e/0x380 net/ipv6/ip6_input.c:310
__netif_receive_skb_one_core+0x115/0x180 net/core/dev.c:5529
__netif_receive_skb+0x1f/0x1b0 net/core/dev.c:5643
netif_receive_skb_internal net/core/dev.c:5729 [inline]
netif_receive_skb+0x133/0x700 net/core/dev.c:5788
tun_rx_batched+0x429/0x780 drivers/net/tun.c:1579
tun_get_user+0x29e3/0x3bc0 drivers/net/tun.c:2002
tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2048
call_write_iter include/linux/fs.h:2020 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x64f/0xdf0 fs/read_write.c:584
ksys_write+0x12f/0x250 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f38e387b82f
Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 b9 80 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 0c 81 02 00 48
RSP: 002b:00007f38e45c9090 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f38e399bf80 RCX: 00007f38e387b82f
RDX: 00000000000003b6 RSI: 0000000020000680 RDI: 00000000000000c8
RBP: 00007f38e38c847a R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000003b6 R11: 0000000000000293 R12: 0000000000000000
R13: 000000000000000b R14: 00007f38e399bf80 R15: 00007f38e3abfa48
</TASK>

Allocated by task 10044:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:374 [inline]
__kasan_kmalloc+0xa2/0xb0 mm/kasan/common.c:383
kasan_kmalloc include/linux/kasan.h:198 [inline]
__do_kmalloc_node mm/slab_common.c:1007 [inline]
__kmalloc+0x59/0x90 mm/slab_common.c:1020
kmalloc include/linux/slab.h:604 [inline]
kzalloc include/linux/slab.h:721 [inline]
fib6_info_alloc+0x40/0x160 net/ipv6/ip6_fib.c:155
ip6_route_info_create+0x337/0x1e70 net/ipv6/route.c:3749
ip6_route_add+0x26/0x150 net/ipv6/route.c:3843
rt6_add_route_info+0x2e7/0x4b0 net/ipv6/route.c:4316
rt6_route_rcv+0x76c/0xbf0 net/ipv6/route.c:985
ndisc_router_discovery+0x138b/0x3560 net/ipv6/ndisc.c:1529
ndisc_rcv+0x3de/0x5f0 net/ipv6/ndisc.c:1856
icmpv6_rcv+0x1470/0x19c0 net/ipv6/icmp.c:979
ip6_protocol_deliver_rcu+0x170/0x13e0 net/ipv6/ip6_input.c:438
ip6_input_finish+0x14f/0x2f0 net/ipv6/ip6_input.c:483
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ip6_input+0xa1/0xc0 net/ipv6/ip6_input.c:492
ip6_mc_input+0x48b/0xf40 net/ipv6/ip6_input.c:586
dst_input include/net/dst.h:461 [inline]
ip6_rcv_finish net/ipv6/ip6_input.c:79 [inline]
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ipv6_rcv+0x24e/0x380 net/ipv6/ip6_input.c:310
__netif_receive_skb_one_core+0x115/0x180 net/core/dev.c:5529
__netif_receive_skb+0x1f/0x1b0 net/core/dev.c:5643
netif_receive_skb_internal net/core/dev.c:5729 [inline]
netif_receive_skb+0x133/0x700 net/core/dev.c:5788
tun_rx_batched+0x429/0x780 drivers/net/tun.c:1579
tun_get_user+0x29e3/0x3bc0 drivers/net/tun.c:2002
tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2048
call_write_iter include/linux/fs.h:2020 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x64f/0xdf0 fs/read_write.c:584
ksys_write+0x12f/0x250 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Freed by task 5123:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:522
____kasan_slab_free mm/kasan/common.c:236 [inline]
____kasan_slab_free+0x15b/0x1b0 mm/kasan/common.c:200
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1800 [inline]
slab_free_freelist_hook+0x114/0x1e0 mm/slub.c:1826
slab_free mm/slub.c:3809 [inline]
__kmem_cache_free+0xc0/0x180 mm/slub.c:3822
rcu_do_batch kernel/rcu/tree.c:2158 [inline]
rcu_core+0x819/0x1680 kernel/rcu/tree.c:2431
__do_softirq+0x21a/0x8de kernel/softirq.c:553

Last potentially related work creation:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
__kasan_record_aux_stack+0xbc/0xd0 mm/kasan/generic.c:492
__call_rcu_common.constprop.0+0x9a/0x7a0 kernel/rcu/tree.c:2681
fib6_info_release include/net/ip6_fib.h:332 [inline]
fib6_info_release include/net/ip6_fib.h:329 [inline]
rt6_route_rcv+0xa4e/0xbf0 net/ipv6/route.c:997
ndisc_router_discovery+0x138b/0x3560 net/ipv6/ndisc.c:1529
ndisc_rcv+0x3de/0x5f0 net/ipv6/ndisc.c:1856
icmpv6_rcv+0x1470/0x19c0 net/ipv6/icmp.c:979
ip6_protocol_deliver_rcu+0x170/0x13e0 net/ipv6/ip6_input.c:438
ip6_input_finish+0x14f/0x2f0 net/ipv6/ip6_input.c:483
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ip6_input+0xa1/0xc0 net/ipv6/ip6_input.c:492
ip6_mc_input+0x48b/0xf40 net/ipv6/ip6_input.c:586
dst_input include/net/dst.h:461 [inline]
ip6_rcv_finish net/ipv6/ip6_input.c:79 [inline]
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ipv6_rcv+0x24e/0x380 net/ipv6/ip6_input.c:310
__netif_receive_skb_one_core+0x115/0x180 net/core/dev.c:5529
__netif_receive_skb+0x1f/0x1b0 net/core/dev.c:5643
netif_receive_skb_internal net/core/dev.c:5729 [inline]
netif_receive_skb+0x133/0x700 net/core/dev.c:5788
tun_rx_batched+0x429/0x780 drivers/net/tun.c:1579
tun_get_user+0x29e3/0x3bc0 drivers/net/tun.c:2002
tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2048
call_write_iter include/linux/fs.h:2020 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x64f/0xdf0 fs/read_write.c:584
ksys_write+0x12f/0x250 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Second to last potentially related work creation:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
__kasan_record_aux_stack+0xbc/0xd0 mm/kasan/generic.c:492
insert_work+0x38/0x230 kernel/workqueue.c:1647
__queue_work+0xcdc/0x11f0 kernel/workqueue.c:1803
call_timer_fn+0x193/0x590 kernel/time/timer.c:1700
expire_timers kernel/time/timer.c:1746 [inline]
__run_timers+0x585/0xb20 kernel/time/timer.c:2022
run_timer_softirq+0x58/0xd0 kernel/time/timer.c:2035
__do_softirq+0x21a/0x8de kernel/softirq.c:553

The buggy address belongs to the object at ffff88802805a800
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 64 bytes inside of
freed 512-byte region [ffff88802805a800, ffff88802805aa00)

The buggy address belongs to the physical page:
page:ffffea0000a01600 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x28058
head:ffffea0000a01600 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888013041c80 ffffea0001e02600 dead000000000002
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 18706, tgid 18699 (syz-executor.2), ts 999991973280, free_ts 996884464281
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x2d0/0x350 mm/page_alloc.c:1537
prep_new_page mm/page_alloc.c:1544 [inline]
get_page_from_freelist+0xa25/0x36d0 mm/page_alloc.c:3312
__alloc_pages+0x22e/0x2420 mm/page_alloc.c:4568
alloc_pages_mpol+0x258/0x5f0 mm/mempolicy.c:2133
alloc_slab_page mm/slub.c:1870 [inline]
allocate_slab mm/slub.c:2017 [inline]
new_slab+0x283/0x3c0 mm/slub.c:2070
___slab_alloc+0x979/0x1500 mm/slub.c:3223
__slab_alloc.constprop.0+0x56/0xa0 mm/slub.c:3322
__slab_alloc_node mm/slub.c:3375 [inline]
slab_alloc_node mm/slub.c:3468 [inline]
__kmem_cache_alloc_node+0x131/0x310 mm/slub.c:3517
__do_kmalloc_node mm/slab_common.c:1006 [inline]
__kmalloc+0x49/0x90 mm/slab_common.c:1020
kmalloc include/linux/slab.h:604 [inline]
kzalloc include/linux/slab.h:721 [inline]
copy_splice_read+0x1ac/0x8f0 fs/splice.c:338
vfs_splice_read fs/splice.c:992 [inline]
vfs_splice_read+0x2ea/0x3b0 fs/splice.c:962
splice_direct_to_actor+0x2a5/0xa30 fs/splice.c:1069
do_splice_direct+0x1af/0x280 fs/splice.c:1194
do_sendfile+0xb3e/0x1310 fs/read_write.c:1254
__do_sys_sendfile64 fs/read_write.c:1322 [inline]
__se_sys_sendfile64 fs/read_write.c:1308 [inline]
__x64_sys_sendfile64+0x1d6/0x220 fs/read_write.c:1308
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1137 [inline]
free_unref_page_prepare+0x4fa/0xaa0 mm/page_alloc.c:2347
free_unref_page_list+0xe6/0xb40 mm/page_alloc.c:2533
release_pages+0x32a/0x14f0 mm/swap.c:1042
tlb_batch_pages_flush+0x9a/0x190 mm/mmu_gather.c:98
tlb_flush_mmu_free mm/mmu_gather.c:293 [inline]
tlb_flush_mmu mm/mmu_gather.c:300 [inline]
tlb_finish_mmu+0x14b/0x6f0 mm/mmu_gather.c:392
exit_mmap+0x38b/0xa70 mm/mmap.c:3321
__mmput+0x12a/0x4d0 kernel/fork.c:1349
mmput+0x62/0x70 kernel/fork.c:1371
exit_mm kernel/exit.c:567 [inline]
do_exit+0x9ad/0x2ae0 kernel/exit.c:858
do_group_exit+0xd4/0x2a0 kernel/exit.c:1021
get_signal+0x23be/0x2790 kernel/signal.c:2904
arch_do_signal_or_restart+0x90/0x7f0 arch/x86/kernel/signal.c:309
exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
exit_to_user_mode_prepare+0x121/0x240 kernel/entry/common.c:204
irqentry_exit_to_user_mode+0xa/0x40 kernel/entry/common.c:309
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20231205173250.2982846-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>