[syzbot] [net?] general protection fault in rtnl_create_link

[syzbot <syzbot+de1c7d68a10e3f123bdd@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    eaa517b77e63 ethtool: cmis_cdb: Fix incorrect read / write..
git tree:       net
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1541f23f980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f2054704dd53fb80
dashboard link: https://syzkaller.appspot.com/bug?extid=de1c7d68a10e3f123bdd
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1429874c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1353f74c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8ff6a34dbd2f/disk-eaa517b7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/80dc0689a89b/vmlinux-eaa517b7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/093b749f228d/bzImage-eaa517b7.xz

The issue was bisected to:

commit 04efcee6ef8d0f01eef495db047e7216d6e6e38f
Author: Stanislav Fomichev <sdf@fomichev.me>
Date:   Fri Apr 4 16:11:22 2025 +0000

    net: hold instance lock during NETDEV_CHANGE

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=151db7e4580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=171db7e4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=131db7e4580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+de1c7d68a10e3f123bdd@syzkaller.appspotmail.com
Fixes: 04efcee6ef8d ("net: hold instance lock during NETDEV_CHANGE")

netlink: 4 bytes leftover after parsing attributes in process `syz-executor402'.
netlink: 'syz-executor402': attribute type 15 has an invalid length.
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000055: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000002a8-0x00000000000002af]
CPU: 0 UID: 0 PID: 5841 Comm: syz-executor402 Not tainted 6.14.0-syzkaller-13348-geaa517b77e63 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
RIP: 0010:netdev_need_ops_lock include/net/netdev_lock.h:33 [inline]
RIP: 0010:netdev_lock_ops include/net/netdev_lock.h:41 [inline]
RIP: 0010:rtnl_create_link+0x6af/0xea0 net/core/rtnetlink.c:3680
Code: 24 20 42 80 3c 28 00 74 08 48 89 df e8 4a 3a 3b f8 4c 89 64 24 28 bd a8 02 00 00 48 89 5c 24 08 48 03 2b 48 89 e8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 ef e8 22 3a 3b f8 45 31 e4 48 83 7d 00
RSP: 0018:ffffc900040b6e70 EFLAGS: 00010206
RAX: 0000000000000055 RBX: ffff888035860008 RCX: ffff888030a01e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00000000000002a8 R08: ffffffff89f245f9 R09: 1ffff92000816dfa
R10: dffffc0000000000 R11: fffff52000816dfb R12: ffff8880212e0080
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff888035860000
FS:  000055556170f380(0000) GS:ffff888124f96000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000045ad50 CR3: 000000007c1d2000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 rtnl_newlink_create+0x2f2/0xcb0 net/core/rtnetlink.c:3826
 __rtnl_newlink net/core/rtnetlink.c:3953 [inline]
 rtnl_newlink+0x18b0/0x1fe0 net/core/rtnetlink.c:4068
 rtnetlink_rcv_msg+0x80f/0xd70 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x208/0x480 net/netlink/af_netlink.c:2534
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x7f8/0x9a0 net/netlink/af_netlink.c:1339
 netlink_sendmsg+0x8c3/0xcd0 net/netlink/af_netlink.c:1883
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg+0x221/0x270 net/socket.c:727
 ____sys_sendmsg+0x523/0x860 net/socket.c:2566
 ___sys_sendmsg net/socket.c:2620 [inline]
 __sys_sendmsg+0x271/0x360 net/socket.c:2652
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff3d9feac39
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe861803d8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff3d9feac39
RDX: 0000000004000000 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000006 R09: 0000000000000006
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000200000000110 R14: 0000200000000088 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:netdev_need_ops_lock include/net/netdev_lock.h:33 [inline]
RIP: 0010:netdev_lock_ops include/net/netdev_lock.h:41 [inline]
RIP: 0010:rtnl_create_link+0x6af/0xea0 net/core/rtnetlink.c:3680
Code: 24 20 42 80 3c 28 00 74 08 48 89 df e8 4a 3a 3b f8 4c 89 64 24 28 bd a8 02 00 00 48 89 5c 24 08 48 03 2b 48 89 e8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 ef e8 22 3a 3b f8 45 31 e4 48 83 7d 00
RSP: 0018:ffffc900040b6e70 EFLAGS: 00010206
RAX: 0000000000000055 RBX: ffff888035860008 RCX: ffff888030a01e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00000000000002a8 R08: ffffffff89f245f9 R09: 1ffff92000816dfa
R10: dffffc0000000000 R11: fffff52000816dfb R12: ffff8880212e0080
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff888035860000
FS:  000055556170f380(0000) GS:ffff888125096000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000140 CR3: 000000007c1d2000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	24 20                	and    $0x20,%al
   2:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1)
   7:	74 08                	je     0x11
   9:	48 89 df             	mov    %rbx,%rdi
   c:	e8 4a 3a 3b f8       	call   0xf83b3a5b
  11:	4c 89 64 24 28       	mov    %r12,0x28(%rsp)
  16:	bd a8 02 00 00       	mov    $0x2a8,%ebp
  1b:	48 89 5c 24 08       	mov    %rbx,0x8(%rsp)
  20:	48 03 2b             	add    (%rbx),%rbp
  23:	48 89 e8             	mov    %rbp,%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 ef             	mov    %rbp,%rdi
  34:	e8 22 3a 3b f8       	call   0xf83b3a5b
  39:	45 31 e4             	xor    %r12d,%r12d
  3c:	48                   	rex.W
  3d:	83                   	.byte 0x83
  3e:	7d 00                	jge    0x40


---
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 syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

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