Re: [syzbot] [net?] general protection fault in ethnl_default_dumpit

[syzbot <syzbot+3da2442641f0c6a705a2@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    2525e16a2bae Merge git://git.kernel.org/pub/scm/linux/kern..
git tree:       net-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=17d9a4b7980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fbc61e4c6e816b7b
dashboard link: https://syzkaller.appspot.com/bug?extid=3da2442641f0c6a705a2
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=14b2aa54580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=178283a8580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bae047feb57e/disk-2525e16a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9f10529c6bdd/vmlinux-2525e16a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8dcb6d0a6029/bzImage-2525e16a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3da2442641f0c6a705a2@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000197: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000cb8-0x0000000000000cbf]
CPU: 1 UID: 0 PID: 5830 Comm: syz-executor357 Not tainted 6.14.0-rc5-syzkaller-01064-g2525e16a2bae #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
RIP: 0010:netdev_need_ops_lock include/linux/netdevice.h:2792 [inline]
RIP: 0010:netdev_lock_ops include/linux/netdevice.h:2803 [inline]
RIP: 0010:ethnl_default_dump_one net/ethtool/netlink.c:557 [inline]
RIP: 0010:ethnl_default_dumpit+0x447/0xd40 net/ethtool/netlink.c:593
Code: 49 8b 1f 48 89 d8 48 c1 e8 03 42 80 3c 30 00 74 08 48 89 df e8 ca e6 17 f8 4c 8b 3b 49 8d 9f bd 0c 00 00 48 89 d8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 0f 85 4b 07 00 00 0f b6 1b 31 ff 89 de e8 f0
RSP: 0018:ffffc9000400f0d8 EFLAGS: 00010203
RAX: 0000000000000197 RBX: 0000000000000cbd RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8c80fdc0 RDI: 0000000000000001
RBP: ffff888033e5ac00 R08: ffffffff903d0b77 R09: 1ffffffff207a16e
R10: dffffc0000000000 R11: fffffbfff207a16f R12: ffff888144ad0600
R13: ffff88802fd3e140 R14: dffffc0000000000 R15: 0000000000000000
FS:  0000555584194380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000400000000a40 CR3: 00000000352bc000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 genl_dumpit+0x10d/0x1b0 net/netlink/genetlink.c:1027
 netlink_dump+0x64d/0xe10 net/netlink/af_netlink.c:2309
 __netlink_dump_start+0x5a2/0x790 net/netlink/af_netlink.c:2424
 genl_family_rcv_msg_dumpit net/netlink/genetlink.c:1076 [inline]
 genl_family_rcv_msg net/netlink/genetlink.c:1192 [inline]
 genl_rcv_msg+0x894/0xec0 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x206/0x480 net/netlink/af_netlink.c:2534
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x7f6/0x990 net/netlink/af_netlink.c:1339
 netlink_sendmsg+0x8de/0xcb0 net/netlink/af_netlink.c:1883
 sock_sendmsg_nosec net/socket.c:709 [inline]
 __sock_sendmsg+0x221/0x270 net/socket.c:724
 ____sys_sendmsg+0x53a/0x860 net/socket.c:2564
 ___sys_sendmsg net/socket.c:2618 [inline]
 __sys_sendmsg+0x269/0x350 net/socket.c:2650
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdb90304329
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffa4264738 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fffa4264908 RCX: 00007fdb90304329
RDX: 0000000000000000 RSI: 0000400000000a40 RDI: 0000000000000003
RBP: 00007fdb90377610 R08: 0000000000000000 R09: 00007fffa4264908
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fffa42648f8 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:netdev_need_ops_lock include/linux/netdevice.h:2792 [inline]
RIP: 0010:netdev_lock_ops include/linux/netdevice.h:2803 [inline]
RIP: 0010:ethnl_default_dump_one net/ethtool/netlink.c:557 [inline]
RIP: 0010:ethnl_default_dumpit+0x447/0xd40 net/ethtool/netlink.c:593
Code: 49 8b 1f 48 89 d8 48 c1 e8 03 42 80 3c 30 00 74 08 48 89 df e8 ca e6 17 f8 4c 8b 3b 49 8d 9f bd 0c 00 00 48 89 d8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 0f 85 4b 07 00 00 0f b6 1b 31 ff 89 de e8 f0
RSP: 0018:ffffc9000400f0d8 EFLAGS: 00010203
RAX: 0000000000000197 RBX: 0000000000000cbd RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8c80fdc0 RDI: 0000000000000001
RBP: ffff888033e5ac00 R08: ffffffff903d0b77 R09: 1ffffffff207a16e
R10: dffffc0000000000 R11: fffffbfff207a16f R12: ffff888144ad0600
R13: ffff88802fd3e140 R14: dffffc0000000000 R15: 0000000000000000
FS:  0000555584194380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000045ad50 CR3: 00000000352bc000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	49 8b 1f             	mov    (%r15),%rbx
   3:	48 89 d8             	mov    %rbx,%rax
   6:	48 c1 e8 03          	shr    $0x3,%rax
   a:	42 80 3c 30 00       	cmpb   $0x0,(%rax,%r14,1)
   f:	74 08                	je     0x19
  11:	48 89 df             	mov    %rbx,%rdi
  14:	e8 ca e6 17 f8       	call   0xf817e6e3
  19:	4c 8b 3b             	mov    (%rbx),%r15
  1c:	49 8d 9f bd 0c 00 00 	lea    0xcbd(%r15),%rbx
  23:	48 89 d8             	mov    %rbx,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 0f b6 04 30       	movzbl (%rax,%r14,1),%eax <-- trapping instruction
  2f:	84 c0                	test   %al,%al
  31:	0f 85 4b 07 00 00    	jne    0x782
  37:	0f b6 1b             	movzbl (%rbx),%ebx
  3a:	31 ff                	xor    %edi,%edi
  3c:	89 de                	mov    %ebx,%esi
  3e:	e8                   	.byte 0xe8
  3f:	f0                   	lock


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