[syzbot] [tls?] general protection fault in handshake_complete

Hello,

syzbot found the following issue on:

HEAD commit:    92fd6e84175b Add linux-next specific files for 20251125
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1416c57c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c8705ffbbff9235f
dashboard link: https://syzkaller.appspot.com/bug?extid=dfffb6c26ee592ff9e83
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17df4f42580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1418a612580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/504ec57bbfb4/disk-92fd6e84.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/90731c1057eb/vmlinux-92fd6e84.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7066fa5b18b8/bzImage-92fd6e84.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
CPU: 1 UID: 0 PID: 6046 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:handshake_complete+0x36/0x350 net/handshake/request.c:288
Code: 54 53 48 83 ec 10 48 89 54 24 08 89 f5 49 89 ff 49 bd 00 00 00 00 00 fc ff df e8 05 5b 6e f6 49 8d 5f 28 48 89 d8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 df e8 ab ab d4 f6 48 8b 1b 4c 8d 63 30
RSP: 0018:ffffc90003447300 EFLAGS: 00010206
RAX: 0000000000000005 RBX: 0000000000000028 RCX: ffff888025ee9e80
RDX: 0000000000000000 RSI: 00000000fffffffb RDI: 0000000000000000
RBP: 00000000fffffffb R08: ffff888027a57103 R09: 1ffff11004f4ae20
R10: dffffc0000000000 R11: ffffed1004f4ae21 R12: ffff88807867a150
R13: dffffc0000000000 R14: dffffc0000000000 R15: 0000000000000000
FS:  0000555565002500(0000) GS:ffff888125b41000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 0000000075f40000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 handshake_nl_accept_doit+0x3c9/0x7f0 net/handshake/netlink.c:128
 genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
 genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec+0x18f/0x1d0 net/socket.c:728
 __sock_sendmsg net/socket.c:743 [inline]
 ____sys_sendmsg+0x577/0x880 net/socket.c:2626
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2680
 __sys_sendmsg net/socket.c:2712 [inline]
 __do_sys_sendmsg net/socket.c:2717 [inline]
 __se_sys_sendmsg net/socket.c:2715 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2715
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdd1638f749
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:00007ffcd38a9ef8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fdd165e5fa0 RCX: 00007fdd1638f749
RDX: 0000000000000000 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 00007fdd16413f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdd165e5fa0 R14: 00007fdd165e5fa0 R15: 0000000000000003
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:handshake_complete+0x36/0x350 net/handshake/request.c:288
Code: 54 53 48 83 ec 10 48 89 54 24 08 89 f5 49 89 ff 49 bd 00 00 00 00 00 fc ff df e8 05 5b 6e f6 49 8d 5f 28 48 89 d8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 df e8 ab ab d4 f6 48 8b 1b 4c 8d 63 30
RSP: 0018:ffffc90003447300 EFLAGS: 00010206
RAX: 0000000000000005 RBX: 0000000000000028 RCX: ffff888025ee9e80
RDX: 0000000000000000 RSI: 00000000fffffffb RDI: 0000000000000000
RBP: 00000000fffffffb R08: ffff888027a57103 R09: 1ffff11004f4ae20
R10: dffffc0000000000 R11: ffffed1004f4ae21 R12: ffff88807867a150
R13: dffffc0000000000 R14: dffffc0000000000 R15: 0000000000000000
FS:  0000555565002500(0000) GS:ffff888125b41000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f52cc6e8286 CR3: 0000000075f40000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	54                   	push   %rsp
   1:	53                   	push   %rbx
   2:	48 83 ec 10          	sub    $0x10,%rsp
   6:	48 89 54 24 08       	mov    %rdx,0x8(%rsp)
   b:	89 f5                	mov    %esi,%ebp
   d:	49 89 ff             	mov    %rdi,%r15
  10:	49 bd 00 00 00 00 00 	movabs $0xdffffc0000000000,%r13
  17:	fc ff df
  1a:	e8 05 5b 6e f6       	call   0xf66e5b24
  1f:	49 8d 5f 28          	lea    0x28(%r15),%rbx
  23:	48 89 d8             	mov    %rbx,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	48 89 df             	mov    %rbx,%rdi
  34:	e8 ab ab d4 f6       	call   0xf6d4abe4
  39:	48 8b 1b             	mov    (%rbx),%rbx
  3c:	4c 8d 63 30          	lea    0x30(%rbx),%r12


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at [email protected].

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup