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

[syzbot <syzbot+89affbc8a292a442d4cb@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    feacb1774bd5 Merge tag 'sched_ext-for-6.16' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16ace6d4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d4c7a3e8691d5cf
dashboard link: https://syzkaller.appspot.com/bug?extid=89affbc8a292a442d4cb
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/73deb6840db8/disk-feacb177.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5908317c8cf4/vmlinux-feacb177.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4ab4d0c65d47/bzImage-feacb177.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+89affbc8a292a442d4cb@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000021: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f]
CPU: 1 UID: 0 PID: 5482 Comm: dhcpcd Not tainted 6.15.0-syzkaller-03589-gfeacb1774bd5 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:read_pnet include/net/net_namespace.h:409 [inline]
RIP: 0010:dev_net include/linux/netdevice.h:2708 [inline]
RIP: 0010:ip_mc_reset net/ipv4/igmp.c:1846 [inline]
RIP: 0010:ip_mc_up+0x76/0x300 net/ipv4/igmp.c:1879
Code: 89 d8 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 3f a7 3e f8 41 be 08 01 00 00 4c 03 33 e8 b1 1e 75 01 4c 89 f0 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 f7 e8 1b a7 3e f8 4d 8b 36 48 8d bb 98
RSP: 0018:ffffc90003bcf6d0 EFLAGS: 00010206
RAX: 0000000000000021 RBX: ffff8880330a5800 RCX: ffff88802eae5a00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 0000000000000001 R08: ffffffff8f2f36a7 R09: 1ffffffff1e5e6d4
R10: dffffc0000000000 R11: fffffbfff1e5e6d5 R12: dffffc0000000000
R13: dffffc0000000000 R14: 0000000000000108 R15: 0000000000000001
FS:  00007f84ecda4740(0000) GS:ffff8881261c0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9187e00000 CR3: 00000000217ac000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 inetdev_event+0xfb3/0x15b0 net/ipv4/devinet.c:1631
 notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2214 [inline]
 call_netdevice_notifiers net/core/dev.c:2228 [inline]
 __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
 netif_change_flags+0xe8/0x1a0 net/core/dev.c:9422
 dev_change_flags+0x130/0x260 net/core/dev_api.c:68
 devinet_ioctl+0xbb4/0x1b50 net/ipv4/devinet.c:1200
 inet_ioctl+0x3c0/0x4c0 net/ipv4/af_inet.c:1001
 sock_do_ioctl+0xd9/0x300 net/socket.c:1190
 sock_ioctl+0x576/0x790 net/socket.c:1311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f84ecea4378
Code: 00 00 48 8d 44 24 08 48 89 54 24 e0 48 89 44 24 c0 48 8d 44 24 d0 48 89 44 24 c8 b8 10 00 00 00 c7 44 24 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 07 89 d0 c3 0f 1f 40 00 48 8b 15 49 3a 0d
RSP: 002b:00007ffd5c4009c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000000001a RCX: 00007f84ecea4378
RDX: 00007ffd5c410bc0 RSI: 0000000000008914 RDI: 000000000000001a
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd5c420d60
R13: 00007f84ecda46c8 R14: 0000000000000028 R15: 0000000000008914
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:read_pnet include/net/net_namespace.h:409 [inline]
RIP: 0010:dev_net include/linux/netdevice.h:2708 [inline]
RIP: 0010:ip_mc_reset net/ipv4/igmp.c:1846 [inline]
RIP: 0010:ip_mc_up+0x76/0x300 net/ipv4/igmp.c:1879
Code: 89 d8 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 3f a7 3e f8 41 be 08 01 00 00 4c 03 33 e8 b1 1e 75 01 4c 89 f0 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 f7 e8 1b a7 3e f8 4d 8b 36 48 8d bb 98
RSP: 0018:ffffc90003bcf6d0 EFLAGS: 00010206
RAX: 0000000000000021 RBX: ffff8880330a5800 RCX: ffff88802eae5a00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 0000000000000001 R08: ffffffff8f2f36a7 R09: 1ffffffff1e5e6d4
R10: dffffc0000000000 R11: fffffbfff1e5e6d5 R12: dffffc0000000000
R13: dffffc0000000000 R14: 0000000000000108 R15: 0000000000000001
FS:  00007f84ecda4740(0000) GS:ffff8881261c0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31206ff8 CR3: 00000000217ac000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	89 d8                	mov    %ebx,%eax
   2:	48 c1 e8 03          	shr    $0x3,%rax
   6:	42 80 3c 20 00       	cmpb   $0x0,(%rax,%r12,1)
   b:	74 08                	je     0x15
   d:	48 89 df             	mov    %rbx,%rdi
  10:	e8 3f a7 3e f8       	call   0xf83ea754
  15:	41 be 08 01 00 00    	mov    $0x108,%r14d
  1b:	4c 03 33             	add    (%rbx),%r14
  1e:	e8 b1 1e 75 01       	call   0x1751ed4
  23:	4c 89 f0             	mov    %r14,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 20 00       	cmpb   $0x0,(%rax,%r12,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	4c 89 f7             	mov    %r14,%rdi
  34:	e8 1b a7 3e f8       	call   0xf83ea754
  39:	4d 8b 36             	mov    (%r14),%r14
  3c:	48                   	rex.W
  3d:	8d                   	.byte 0x8d
  3e:	bb                   	.byte 0xbb
  3f:	98                   	cwtl


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