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BUG: KFENCE: use-after-free read in xfrm_alloc_spi+0x3b9/0xf30

Use-after-free read at 0xffff8881365ae0c4 (in kfence-#214):
 xfrm_alloc_spi+0x3b9/0xf30
 xfrm_alloc_userspi+0x70b/0xc90
 xfrm_user_rcv_msg+0x7a3/0xab0
 netlink_rcv_skb+0x208/0x470
 xfrm_netlink_rcv+0x79/0x90
 netlink_unicast+0x82f/0x9e0
 netlink_sendmsg+0x805/0xb30
 __sock_sendmsg+0x21c/0x270
 ____sys_sendmsg+0x505/0x830
 ___sys_sendmsg+0x21f/0x2a0
 __x64_sys_sendmsg+0x19b/0x260
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

kfence-#214: 0xffff8881365ae000-0xffff8881365ae0ff, size=256, cache=vm_area_struct

allocated by task 15728 on cpu 0 at 246.284928s (3.179705s ago):
 vm_area_alloc+0x24/0x140
 mmap_region+0xdc7/0x20c0
 do_mmap+0xc45/0x10d0
 vm_mmap_pgoff+0x2a6/0x4d0
 ksys_mmap_pgoff+0x51f/0x760
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

freed by task 15728 on cpu 0 at 246.309400s (3.171495s ago):
 exit_mmap+0x53f/0xb50
 __mmput+0x118/0x430
 exit_mm+0x1da/0x2c0
 do_exit+0x648/0x2300
 do_group_exit+0x21c/0x2d0
 __x64_sys_exit_group+0x3f/0x40
 x64_sys_call+0x21f7/0x2200
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 0 UID: 0 PID: 15968 Comm: syz.1.4178 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:xfrm_alloc_spi+0x3b9/0xf30
Code: c1 08 c1 74 0a e8 87 79 9d f7 e9 14 02 00 00 49 8d 9d c4 00 00 00 48 89 d8 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 9f 01 00 00 <8b> 1b 89 df 44 89 f6 e8 1b 7b 9d f7 44 39 f3 0f 85 df 00 00 00 49
RSP: 0018:ffffc9000378f0e0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8881365ae0c4 RCX: 0000000000080000
RDX: ffffc9000937a000 RSI: 000000000000026d RDI: 000000000000026e
RBP: ffffc9000378f230 R08: 0000000000000000 R09: ffffffff8a224480
R10: dffffc0000000000 R11: fffff520006f1e0c R12: dffffc0000000000
R13: ffff8881365ae000 R14: 0000000000000000 R15: ffffc9000378f6a0
FS:  00007fb309a866c0(0000) GS:ffff8880b8615000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff8881365ae0c4 CR3: 000000012effe000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 xfrm_alloc_userspi+0x70b/0xc90
 xfrm_user_rcv_msg+0x7a3/0xab0
 netlink_rcv_skb+0x208/0x470
 xfrm_netlink_rcv+0x79/0x90
 netlink_unicast+0x82f/0x9e0
 netlink_sendmsg+0x805/0xb30
 __sock_sendmsg+0x21c/0x270
 ____sys_sendmsg+0x505/0x830
 ___sys_sendmsg+0x21f/0x2a0
 __x64_sys_sendmsg+0x19b/0x260
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb308b8eba9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb309a86038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fb308dd5fa0 RCX: 00007fb308b8eba9
RDX: 0000000000000000 RSI: 0000200000000540 RDI: 0000000000000003
RBP: 00007fb308c11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb308dd6038 R14: 00007fb308dd5fa0 R15: 00007ffee191c988
 </TASK>
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