Re: KASAN: use-after-free Write in __xfrm_policy_unlink

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    a9cd3439e3c6 neighbor: Use nda_policy for validating attri..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16ff4a0d400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1f6442435a55ea09
dashboard link: https://syzkaller.appspot.com/bug?extid=9d971dd21eb26567036b
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=118c7e1b400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+9d971dd21eb26567036b@xxxxxxxxxxxxxxxxxxxxxxxxx

8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:704 [inline]
BUG: KASAN: use-after-free in hlist_del_rcu include/linux/rculist.h:455  
[inline]
BUG: KASAN: use-after-free in __xfrm_policy_unlink+0xa09/0xa20  
net/xfrm/xfrm_policy.c:2215
Write of size 8 at addr ffff8881b7071b50 by task syz-executor3/7764

CPU: 0 PID: 7764 Comm: syz-executor3 Not tainted 4.20.0-rc6+ #355
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+0x244/0x39d lib/dump_stack.c:113
 print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
 __asan_report_store8_noabort+0x17/0x20 mm/kasan/report.c:438
 __hlist_del include/linux/list.h:704 [inline]
 hlist_del_rcu include/linux/rculist.h:455 [inline]
 __xfrm_policy_unlink+0xa09/0xa20 net/xfrm/xfrm_policy.c:2215
 xfrm_policy_insert+0x20a/0x850 net/xfrm/xfrm_policy.c:1587
 pfkey_spdadd+0x10f8/0x19d0 net/key/af_key.c:2339
 pfkey_process+0x851/0x9a0 net/key/af_key.c:2844
 pfkey_sendmsg+0x5df/0xfb0 net/key/af_key.c:3683
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:631
 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2116
 __sys_sendmsg+0x11d/0x280 net/socket.c:2154
 __do_sys_sendmsg net/socket.c:2163 [inline]
 __se_sys_sendmsg net/socket.c:2161 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457669
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fea87c1ac78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457669
RDX: 0000000000000000 RSI: 0000000020000000 RDI: 0000000000000003
RBP: 000000000072bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fea87c1b6d4
R13: 00000000004c443a R14: 00000000004d7410 R15: 00000000ffffffff

Allocated by task 7736:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
 kmem_cache_alloc_trace+0x152/0x750 mm/slab.c:3620
 kmalloc include/linux/slab.h:546 [inline]
 kzalloc include/linux/slab.h:741 [inline]
 xfrm_policy_alloc+0xfa/0x4f0 net/xfrm/xfrm_policy.c:383
 pfkey_spdadd+0x244/0x19d0 net/key/af_key.c:2272
 pfkey_process+0x851/0x9a0 net/key/af_key.c:2844
 pfkey_sendmsg+0x5df/0xfb0 net/key/af_key.c:3683
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:631
 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2116
 __sys_sendmsg+0x11d/0x280 net/socket.c:2154
 __do_sys_sendmsg net/socket.c:2163 [inline]
 __se_sys_sendmsg net/socket.c:2161 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 7753:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
 __cache_free mm/slab.c:3498 [inline]
 kfree+0xcf/0x230 mm/slab.c:3817
 xfrm_policy_destroy_rcu+0x4a/0x60 net/xfrm/xfrm_policy.c:407
 __rcu_reclaim kernel/rcu/rcu.h:240 [inline]
 rcu_do_batch kernel/rcu/tree.c:2437 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2716 [inline]
 rcu_process_callbacks+0x100a/0x1ac0 kernel/rcu/tree.c:2697
 __do_softirq+0x308/0xb7e kernel/softirq.c:292

The buggy address belongs to the object at ffff8881b7071b40
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 16 bytes inside of
 1024-byte region [ffff8881b7071b40, ffff8881b7071f40)
The buggy address belongs to the page:
page:ffffea0006dc1c00 count:1 mapcount:0 mapping:ffff8881da800ac0 index:0x0  
compound_mapcount: 0
flags: 0x2fffc0000010200(slab|head)
raw: 02fffc0000010200 ffffea0006da2088 ffffea0007624d08 ffff8881da800ac0
raw: 0000000000000000 ffff8881b7070040 0000000100000007 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881b7071a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881b7071a80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff8881b7071b00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                 ^
 ffff8881b7071b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881b7071c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================