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SubjectRe: KASAN: use-after-free Write in __xfrm_policy_unlink
From
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@syzkaller.appspotmail.com

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
==================================================================

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