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SubjectKASAN: use-after-free Write in __xfrm_policy_unlink

syzbot found the following crash on:

HEAD commit: fcaccc829382 liquidio: correct error msg text when removin..
git tree: net-next
console output:
kernel config:
dashboard link:
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

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:

BUG: KASAN: use-after-free in __write_once_size
include/linux/compiler.h:215 [inline]
BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:679 [inline]
BUG: KASAN: use-after-free in hlist_del_rcu include/linux/rculist.h:440
BUG: KASAN: use-after-free in __xfrm_policy_unlink+0x735/0x7e0
Write of size 8 at addr ffff8801a94744c8 by task swapper/0/0

CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.18.0-rc3+ #126
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+0x1c9/0x2b4 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
__asan_report_store8_noabort+0x17/0x20 mm/kasan/report.c:438
__write_once_size include/linux/compiler.h:215 [inline]
__hlist_del include/linux/list.h:679 [inline]
hlist_del_rcu include/linux/rculist.h:440 [inline]
__xfrm_policy_unlink+0x735/0x7e0 net/xfrm/xfrm_policy.c:1222
xfrm_policy_delete+0x49/0x90 net/xfrm/xfrm_policy.c:1247
xfrm_policy_timer+0x453/0x670 net/xfrm/xfrm_policy.c:247
call_timer_fn+0x242/0x970 kernel/time/timer.c:1326
expire_timers kernel/time/timer.c:1363 [inline]
__run_timers+0x7a6/0xc70 kernel/time/timer.c:1666
run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
__do_softirq+0x2e8/0xb17 kernel/softirq.c:288
invoke_softirq kernel/softirq.c:368 [inline]
irq_exit+0x1d1/0x200 kernel/softirq.c:408
exiting_irq arch/x86/include/asm/apic.h:527 [inline]
smp_apic_timer_interrupt+0x186/0x730 arch/x86/kernel/apic/apic.c:1052
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54
Code: c7 48 89 45 d8 e8 8a 2d 23 fa 48 8b 45 d8 e9 d2 fe ff ff 48 89 df e8
79 2d 23 fa eb 8a 90 90 90 90 90 90 90 55 48 89 e5 fb f4 <5d> c3 0f 1f 84
00 00 00 00 00 55 48 89 e5 f4 5d c3 90 90 90 90 90
RSP: 0018:ffffffff88e07bc0 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
RAX: dffffc0000000000 RBX: 1ffffffff11c0f7b RCX: ffffffff81667982
RDX: 1ffffffff11e3610 RSI: 0000000000000004 RDI: ffffffff88f1b080
RBP: ffffffff88e07bc0 R08: ffffed003b5c46d7 R09: ffffed003b5c46d6
R10: ffffed003b5c46d6 R11: ffff8801dae236b3 R12: 0000000000000000
R13: ffffffff88e07c78 R14: ffffffff899ee920 R15: 0000000000000000
arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
default_idle+0xc7/0x450 arch/x86/kernel/process.c:500
arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:491
default_idle_call+0x6d/0x90 kernel/sched/idle.c:93
cpuidle_idle_call kernel/sched/idle.c:153 [inline]
do_idle+0x3aa/0x570 kernel/sched/idle.c:262
cpu_startup_entry+0x10c/0x120 kernel/sched/idle.c:368
rest_init+0xe1/0xe4 init/main.c:442
start_kernel+0x90e/0x949 init/main.c:738
x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:452
x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:433
secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:242

Allocated by task 30004:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
kmem_cache_alloc_trace+0x152/0x780 mm/slab.c:3620
kmalloc include/linux/slab.h:513 [inline]
kzalloc include/linux/slab.h:707 [inline]
xfrm_policy_alloc+0xd9/0x480 net/xfrm/xfrm_policy.c:260
xfrm_policy_construct+0x2f/0x590 net/xfrm/xfrm_user.c:1545
xfrm_add_policy+0x20f/0x750 net/xfrm/xfrm_user.c:1591
xfrm_user_rcv_msg+0x455/0x8b0 net/xfrm/xfrm_user.c:2590
netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2448
xfrm_netlink_rcv+0x6f/0x90 net/xfrm/xfrm_user.c:2598
netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
netlink_unicast+0x5a0/0x760 net/netlink/af_netlink.c:1336
netlink_sendmsg+0xa18/0xfc0 net/netlink/af_netlink.c:1901
sock_sendmsg_nosec net/socket.c:641 [inline]
sock_sendmsg+0xd5/0x120 net/socket.c:651
___sys_sendmsg+0x7fd/0x930 net/socket.c:2125
__sys_sendmsg+0x11d/0x290 net/socket.c:2163
__do_sys_sendmsg net/socket.c:2172 [inline]
__se_sys_sendmsg net/socket.c:2170 [inline]
__x64_sys_sendmsg+0x78/0xb0 net/socket.c:2170
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290

Freed by task 516:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xd9/0x260 mm/slab.c:3813
xfrm_policy_destroy_rcu+0x4a/0x60 net/xfrm/xfrm_policy.c:283
__rcu_reclaim kernel/rcu/rcu.h:178 [inline]
rcu_do_batch kernel/rcu/tree.c:2558 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2818 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2785 [inline]
rcu_process_callbacks+0xed5/0x1850 kernel/rcu/tree.c:2802
__do_softirq+0x2e8/0xb17 kernel/softirq.c:288

The buggy address belongs to the object at ffff8801a94744c0
which belongs to the cache kmalloc-1024 of size 1024
The buggy address is located 8 bytes inside of
1024-byte region [ffff8801a94744c0, ffff8801a94748c0)
The buggy address belongs to the page:
page:ffffea0006a51d00 count:1 mapcount:0 mapping:ffff8801da800ac0
index:0xffff8801a9475b40 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffffea0006ae8a08 ffffea00075d3c08 ffff8801da800ac0
raw: ffff8801a9475b40 ffff8801a9474040 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801a9474380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801a9474400: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff8801a9474480: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
ffff8801a9474500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801a9474580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

This bug is generated by a bot. It may contain errors.
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