[syzbot] [net?] general protection fault in add_grec (2)

[syzbot <syzbot+2d29aae505225ce697ee@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    64980441d269 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=169cf40c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=26abb92f9ef9d1d0
dashboard link: https://syzkaller.appspot.com/bug?extid=2d29aae505225ce697ee
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6f87fde80a0d/disk-64980441.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0f721fc8ffe8/vmlinux-64980441.xz
kernel image: https://storage.googleapis.com/syzbot-assets/50b2b318eca4/bzImage-64980441.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2d29aae505225ce697ee@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc001fffe000: 0000 [#1] SMP KASAN PTI
KASAN: probably user-memory-access in range [0x00000000ffff0000-0x00000000ffff0007]
CPU: 1 UID: 0 PID: 5815 Comm: kworker/1:3 Not tainted 6.15.0-syzkaller-12058-g64980441d269 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: mld mld_ifc_work
RIP: 0010:add_grec+0x764/0x1670 net/ipv6/mcast.c:1967
Code: 40 01 41 89 c7 31 ff 89 c6 e8 08 b3 a2 f7 45 85 ff 0f 84 b0 00 00 00 e8 ba ae a2 f7 eb 05 e8 b3 ae a2 f7 49 89 ee 49 c1 ee 03 <43> 80 3c 26 00 74 08 48 89 ef e8 9d f5 03 f8 48 8b 45 00 48 89 84
RSP: 0018:ffffc9000425f8f8 EFLAGS: 00010206
RAX: ffffffff8a1d9c16 RBX: 0000000000000000 RCX: ffff888027a33c00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 00000000ffff0000 R08: ffff888027a33c00 R09: 0000000000000002
R10: 0000000000000004 R11: 0000000000000000 R12: dffffc0000000000
R13: 0000000000000005 R14: 000000001fffe000 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888125d89000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f84328dc0d1 CR3: 000000006bf3c000 CR4: 00000000003526f0
DR0: 0000000000000007 DR1: 000000000000000b DR2: 0000000000000002
DR3: 0000000000000009 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 mld_send_cr net/ipv6/mcast.c:2155 [inline]
 mld_ifc_work+0x671/0xde0 net/ipv6/mcast.c:2702
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xade/0x17b0 kernel/workqueue.c:3321
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:add_grec+0x764/0x1670 net/ipv6/mcast.c:1967
Code: 40 01 41 89 c7 31 ff 89 c6 e8 08 b3 a2 f7 45 85 ff 0f 84 b0 00 00 00 e8 ba ae a2 f7 eb 05 e8 b3 ae a2 f7 49 89 ee 49 c1 ee 03 <43> 80 3c 26 00 74 08 48 89 ef e8 9d f5 03 f8 48 8b 45 00 48 89 84
RSP: 0018:ffffc9000425f8f8 EFLAGS: 00010206
RAX: ffffffff8a1d9c16 RBX: 0000000000000000 RCX: ffff888027a33c00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 00000000ffff0000 R08: ffff888027a33c00 R09: 0000000000000002
R10: 0000000000000004 R11: 0000000000000000 R12: dffffc0000000000
R13: 0000000000000005 R14: 000000001fffe000 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888125d89000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f84328dc0d1 CR3: 00000000736c2000 CR4: 00000000003526f0
DR0: 0000000000000007 DR1: 000000000000000b DR2: 0000000000000002
DR3: 0000000000000009 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	41 89 c7             	mov    %eax,%r15d
   3:	31 ff                	xor    %edi,%edi
   5:	89 c6                	mov    %eax,%esi
   7:	e8 08 b3 a2 f7       	call   0xf7a2b314
   c:	45 85 ff             	test   %r15d,%r15d
   f:	0f 84 b0 00 00 00    	je     0xc5
  15:	e8 ba ae a2 f7       	call   0xf7a2aed4
  1a:	eb 05                	jmp    0x21
  1c:	e8 b3 ae a2 f7       	call   0xf7a2aed4
  21:	49 89 ee             	mov    %rbp,%r14
  24:	49 c1 ee 03          	shr    $0x3,%r14
* 28:	43 80 3c 26 00       	cmpb   $0x0,(%r14,%r12,1) <-- trapping instruction
  2d:	74 08                	je     0x37
  2f:	48 89 ef             	mov    %rbp,%rdi
  32:	e8 9d f5 03 f8       	call   0xf803f5d4
  37:	48 8b 45 00          	mov    0x0(%rbp),%rax
  3b:	48                   	rex.W
  3c:	89                   	.byte 0x89
  3d:	84                   	.byte 0x84


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