linux-kernel - [syzbot] [net?] general protection fault in llc_mac_hdr

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Message-ID: <689b9748.050a0220.51d73.00b6.GAE@google.com>
Date: Tue, 12 Aug 2025 12:34:32 -0700
From: syzbot <syzbot+5da6dcdc18849d9fa01e@...kaller.appspotmail.com>
To: davem@...emloft.net, edumazet@...gle.com, horms@...nel.org, 
	kuba@...nel.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	pabeni@...hat.com, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [net?] general protection fault in llc_mac_hdr_init

Hello,

syzbot found the following issue on:

HEAD commit:    37816488247d Merge tag 'net-6.17-rc1' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14cd61a2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=658effe8a2c01c74
dashboard link: https://syzkaller.appspot.com/bug?extid=5da6dcdc18849d9fa01e
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8430292542cd/disk-37816488.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/69cd308fcca9/vmlinux-37816488.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a39d85d0b6c2/bzImage-37816488.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5da6dcdc18849d9fa01e@...kaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc000ad6eb84: 0000 [#1] SMP KASAN NOPTI
KASAN: probably user-memory-access in range [0x0000000056b75c20-0x0000000056b75c27]
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.16.0-syzkaller-12063-g37816488247d #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:llc_mac_hdr_init+0x2f/0x1a0 net/llc/llc_output.c:30
Code: 56 49 89 f6 41 55 49 89 d5 41 54 55 53 48 89 fb e8 16 2d 30 f8 48 8d 7b 10 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 3b 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b
RSP: 0018:ffffc90000a08c28 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000056b75c10 RCX: ffffffff81a7e2de
RDX: 000000000ad6eb84 RSI: ffffffff898b660a RDI: 0000000056b75c20
RBP: ffff888056b75c10 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 1ffff9200014118f
R13: ffff88801e2ea440 R14: ffffffff81a7df41 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8881247c4000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b3200fff8 CR3: 0000000027c8f000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 llc_conn_ac_send_i_rsp_f_set_ackpf net/llc/llc_c_ac.c:920 [inline]
 llc_conn_ac_send_i_as_ack+0x31c/0x900 net/llc/llc_c_ac.c:945
 </IRQ>
 <TASK>
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:llc_mac_hdr_init+0x2f/0x1a0 net/llc/llc_output.c:30
Code: 56 49 89 f6 41 55 49 89 d5 41 54 55 53 48 89 fb e8 16 2d 30 f8 48 8d 7b 10 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 3b 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b
RSP: 0018:ffffc90000a08c28 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000056b75c10 RCX: ffffffff81a7e2de
RDX: 000000000ad6eb84 RSI: ffffffff898b660a RDI: 0000000056b75c20
RBP: ffff888056b75c10 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 1ffff9200014118f
R13: ffff88801e2ea440 R14: ffffffff81a7df41 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8881247c4000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b3200fff8 CR3: 0000000027c8f000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	56                   	push   %rsi
   1:	49 89 f6             	mov    %rsi,%r14
   4:	41 55                	push   %r13
   6:	49 89 d5             	mov    %rdx,%r13
   9:	41 54                	push   %r12
   b:	55                   	push   %rbp
   c:	53                   	push   %rbx
   d:	48 89 fb             	mov    %rdi,%rbx
  10:	e8 16 2d 30 f8       	call   0xf8302d2b
  15:	48 8d 7b 10          	lea    0x10(%rbx),%rdi
  19:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  20:	fc ff df
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2e:	0f 85 3b 01 00 00    	jne    0x16f
  34:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  3b:	fc ff df
  3e:	48                   	rex.W
  3f:	8b                   	.byte 0x8b


---
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