Re: WARNING in xfrm_alloc_compat

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    4e78c578 Add linux-next specific files for 20201030
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13284492500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=83318758268dc331
dashboard link: https://syzkaller.appspot.com/bug?extid=a7e701c8385bd8543074
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10191ea2500000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1172adf4500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a7e701c8385bd8543074@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
unsupported nla_type 0
WARNING: CPU: 0 PID: 8479 at net/xfrm/xfrm_compat.c:279 xfrm_xlate64_attr net/xfrm/xfrm_compat.c:279 [inline]
WARNING: CPU: 0 PID: 8479 at net/xfrm/xfrm_compat.c:279 xfrm_xlate64 net/xfrm/xfrm_compat.c:300 [inline]
WARNING: CPU: 0 PID: 8479 at net/xfrm/xfrm_compat.c:279 xfrm_alloc_compat+0xf39/0x10d0 net/xfrm/xfrm_compat.c:327
Modules linked in:
CPU: 1 PID: 8479 Comm: syz-executor174 Not tainted 5.10.0-rc1-next-20201030-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:xfrm_xlate64_attr net/xfrm/xfrm_compat.c:279 [inline]
RIP: 0010:xfrm_xlate64 net/xfrm/xfrm_compat.c:300 [inline]
RIP: 0010:xfrm_alloc_compat+0xf39/0x10d0 net/xfrm/xfrm_compat.c:327
Code: de e8 3b 4a d2 f9 84 db 0f 85 b0 f8 ff ff e8 1e 52 d2 f9 8b 74 24 08 48 c7 c7 20 e5 51 8a c6 05 3b eb 3a 05 01 e8 e3 f2 0e 01 <0f> 0b e9 8d f8 ff ff e8 fb 51 d2 f9 8b 14 24 48 c7 c7 e0 e4 51 8a
RSP: 0018:ffffc900015cf378 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff888021221a80 RSI: ffffffff8158ed95 RDI: fffff520002b9e61
RBP: 000000000000000c R08: 0000000000000001 R09: ffff8880b9e2005b
R10: 0000000000000000 R11: 0000000000000000 R12: 00000000ffffffa1
R13: ffff888143d890f8 R14: ffff88801b8b4780 R15: ffff88802148c000
FS:  00000000017d3880(0000) GS:ffff8880b9f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd917a6b6c0 CR3: 000000001f6a2000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 xfrm_alloc_userspi+0x66a/0xa30 net/xfrm/xfrm_user.c:1388
 xfrm_user_rcv_msg+0x42f/0x8b0 net/xfrm/xfrm_user.c:2752
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
 xfrm_netlink_rcv+0x6b/0x90 net/xfrm/xfrm_user.c:2764
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:671
 ____sys_sendmsg+0x331/0x810 net/socket.c:2362
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2416
 __sys_sendmmsg+0x195/0x470 net/socket.c:2506
 __do_sys_sendmmsg net/socket.c:2535 [inline]
 __se_sys_sendmmsg net/socket.c:2532 [inline]
 __x64_sys_sendmmsg+0x99/0x100 net/socket.c:2532
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x440339
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 7b 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffcd04d1fc8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440339
RDX: 00000000000000f1 RSI: 0000000020000180 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401b40
R13: 0000000000401bd0 R14: 0000000000000000 R15: 0000000000000000