[syzbot ci] Re: rtnetlink: RTNL avoidance in rtnl_getlink() and rtnl_dump_ifinfo()

[syzbot ci <syzbot+cid69f1bad2452c7b2@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v4] rtnetlink: RTNL avoidance in rtnl_getlink() and rtnl_dump_ifinfo()
https://lore.kernel.org/all/20260522173002.2181677-1-edumazet@google.com
* [PATCH v4 net-next 1/5] rtnetlink: use nla_nest_end_safe() in rtnl_fill_prop_list()
* [PATCH v4 net-next 2/5] net: defer netdev_name_node_alt_flush() call to netdev_run_todo()
* [PATCH v4 net-next 3/5] rtnetlink: do not acquire RTNL in rtnl_getlink() with RTEXT_FILTER_NAME_ONLY
* [PATCH v4 net-next 4/5] rtnetlink: do not assume RTNL is held in link_master_filtered()
* [PATCH v4 net-next 5/5] rtnetlink: add RTEXT_FILTER_NAME_ONLY support to rtnl_dump_ifinfo()

and found the following issue:
WARNING in rtmsg_ifinfo_build_skb

Full report is available here:
https://ci.syzbot.org/series/583940d4-d5e9-48ca-a2e6-544edbb1d63c

***

WARNING in rtmsg_ifinfo_build_skb

tree:      net-next
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net-next.git
base:      1a1f055318d82e64485a6ff8420e5f70b4267998
arch:      amd64
compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config:    https://ci.syzbot.org/builds/513a249e-70b7-4622-8d72-6f62840955c7/config

pci 0000:00:01.0: BAR 2 [mem 0xfebf0000-0xfebf0fff]
pci 0000:00:01.0: ROM [mem 0xfebe0000-0xfebeffff pref]
pci 0000:00:01.0: Video device with shadowed ROM at [mem 0x000c0000-0x000dffff]
pci 0000:00:02.0: [1af4:1005] type 00 class 0x00ff00 conventional PCI endpoint
pci 0000:00:02.0: BAR 0 [io  0xc080-0xc09f]
pci 0000:00:02.0: BAR 1 [mem 0xfebf1000-0xfebf1fff]
pci 0000:00:02.0: BAR 4 [mem 0xfe000000-0xfe003fff 64bit pref]
pci 0000:00:03.0: [8086:100e] type 00 class 0x020000 conventional PCI endpoint
pci 0000:00:03.0: BAR 0 [mem 0xfebc0000-0xfebdffff]
pci 0000:00:03.0: BAR 1 [io  0xc000-0xc03f]
pci 0000:00:03.0: ROM [mem 0xfeb80000-0xfebbffff pref]
pci 0000:00:1f.0: [8086:2918] type 00 class 0x060100 conventional PCI endpoint
pci 0000:00:1f.0: quirk: [io  0x0600-0x067f] claimed by ICH6 ACPI/GPIO/TCO
pci 0000:00:1f.2: [8086:2922] type 00 class 0x010601 conventional PCI endpoint
pci 0000:00:1f.2: BAR 4 [io  0xc0a0-0xc0bf]
pci 0000:00:1f.2: BAR 5 [mem 0xfebf2000-0xfebf2fff]
pci 0000:00:1f.3: [8086:2930] type 00 class 0x0c0500 conventional PCI endpoint
pci 0000:00:1f.3: BAR 4 [io  0x0700-0x073f]
ACPI: PCI: Interrupt link LNKA configured for IRQ 10
ACPI: PCI: Interrupt link LNKB configured for IRQ 10
ACPI: PCI: Interrupt link LNKC configured for IRQ 11
ACPI: PCI: Interrupt link LNKD configured for IRQ 11
ACPI: PCI: Interrupt link LNKE configured for IRQ 10
ACPI: PCI: Interrupt link LNKF configured for IRQ 10
ACPI: PCI: Interrupt link LNKG configured for IRQ 11
ACPI: PCI: Interrupt link LNKH configured for IRQ 11
ACPI: PCI: Interrupt link GSIA configured for IRQ 16
ACPI: PCI: Interrupt link GSIB configured for IRQ 17
ACPI: PCI: Interrupt link GSIC configured for IRQ 18
ACPI: PCI: Interrupt link GSID configured for IRQ 19
ACPI: PCI: Interrupt link GSIE configured for IRQ 20
ACPI: PCI: Interrupt link GSIF configured for IRQ 21
ACPI: PCI: Interrupt link GSIG configured for IRQ 22
ACPI: PCI: Interrupt link GSIH configured for IRQ 23
iommu: Default domain type: Translated
iommu: DMA domain TLB invalidation policy: lazy mode
SCSI subsystem initialized
ACPI: bus type USB registered
usbcore: registered new interface driver usbfs
usbcore: registered new interface driver hub
usbcore: registered new device driver usb
mc: Linux media interface: v0.10
videodev: Linux video capture interface: v2.00
pps_core: LinuxPPS API ver. 1 registered
pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it>
PTP clock support registered
EDAC MC: Ver: 3.0.0
Advanced Linux Sound Architecture Driver Initialized.
------------[ cut here ]------------
err == -EMSGSIZE
WARNING: net/core/rtnetlink.c:4524 at rtmsg_ifinfo_build_skb+0x218/0x260, CPU#0: swapper/0/1
Modules linked in:
CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:rtmsg_ifinfo_build_skb+0x218/0x260
Code: f6 ba 01 00 00 00 89 e9 e8 45 ac 3a 00 4c 89 f0 48 83 c4 30 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc e8 39 dc 40 f8 90 <0f> 0b 90 eb 90 89 d9 80 e1 07 fe c1 38 c1 0f 8c 95 fe ff ff 48 89
RSP: 0000:ffffc90000067438 EFLAGS: 00010293
RAX: ffffffff8984e887 RBX: 0000000000000000 RCX: ffff8881026f5880
RDX: 0000000000000000 RSI: 00000000ffffffa6 RDI: 00000000ffffffa6
RBP: 00000000ffffffa6 R08: ffffffff8984f746 R09: 0000000000000000
R10: fffff5200000ce30 R11: ffffed1020c50405 R12: 1ffff11020c51c21
R13: 0000000000000000 R14: ffff888103a82480 R15: ffff88810628e000
FS:  0000000000000000(0000) GS:ffff88818dc76000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88823ffff000 CR3: 000000000e74a000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 rtmsg_ifinfo+0x8c/0x1a0
 register_netdevice+0x1aca/0x1ec0
 register_netdev+0x40/0x60
 loopback_net_init+0x75/0x150
 ops_init+0x35c/0x5c0
 register_pernet_operations+0x343/0x830
 register_pernet_device+0x2a/0x80
 net_dev_init+0x973/0xa90
 do_one_initcall+0x250/0x870
 do_initcall_level+0x104/0x190
 do_initcalls+0x59/0xa0
 kernel_init_freeable+0x2a6/0x3e0
 kernel_init+0x1d/0x1d0
 ret_from_fork+0x514/0xb70
 ret_from_fork_asm+0x1a/0x30
 </TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

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