[syzbot ci] Re: ipv6: route: fix adding routes via the loopback device

[syzbot ci <syzbot+cidbf3efe2a5ca243b@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v1] ipv6: route: fix adding routes via the loopback device
https://lore.kernel.org/all/20260930152229.1453929-1-hengyul@cs.unc.edu
* [PATCH net 1/2] ipv6: route: do not validate nexthop of routes promoted to reject routes
* [PATCH net 2/2] selftests: net: fib_tests: add tests for IPv6 routes via loopback device

and found the following issue:
WARNING in nsim_fib_event_nb

Full report is available here:
https://ci.syzbot.org/series/7c566bff-eca1-4b49-90ae-6537c6011730

***

WARNING in nsim_fib_event_nb

tree:      net
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net.git
base:      e23a64eb244356ee47c0620f0722d51bd88db522
arch:      amd64
compiler:  Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
config:    https://ci.syzbot.org/builds/ef50b46f-5dab-4a9c-943a-321047ec0627/config
syz repro: https://ci.syzbot.org/findings/96331068-e137-4de8-85a3-65ac3caafea0/syz_repro

------------[ cut here ]------------
i != fen6_info->nsiblings
WARNING: drivers/net/netdevsim/fib.c:831 at nsim_fib6_event_init drivers/net/netdevsim/fib.c:831 [inline], CPU#1: syz.2.19/5834
WARNING: drivers/net/netdevsim/fib.c:831 at nsim_fib6_prepare_event drivers/net/netdevsim/fib.c:947 [inline], CPU#1: syz.2.19/5834
WARNING: drivers/net/netdevsim/fib.c:831 at nsim_fib_event_schedule_work drivers/net/netdevsim/fib.c:1003 [inline], CPU#1: syz.2.19/5834
WARNING: drivers/net/netdevsim/fib.c:831 at nsim_fib_event_nb+0x1029/0x11d0 drivers/net/netdevsim/fib.c:1043, CPU#1: syz.2.19/5834
Modules linked in:
CPU: 1 UID: 0 PID: 5834 Comm: syz.2.19 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:nsim_fib6_event_init drivers/net/netdevsim/fib.c:831 [inline]
RIP: 0010:nsim_fib6_prepare_event drivers/net/netdevsim/fib.c:947 [inline]
RIP: 0010:nsim_fib_event_schedule_work drivers/net/netdevsim/fib.c:1003 [inline]
RIP: 0010:nsim_fib_event_nb+0x1029/0x11d0 drivers/net/netdevsim/fib.c:1043
Code: eb 0d 4d 89 fd e8 97 75 6e fa be 01 00 00 00 48 89 df e8 aa db 85 fd 4d 89 ef 4c 8b 6c 24 20 e9 4a f3 ff ff e8 78 75 6e fa 90 <0f> 0b 90 e9 db fa ff ff 89 e9 80 e1 07 80 c1 03 38 c1 0f 8c df f0
RSP: 0018:ffffc9000388f030 EFLAGS: 00010293
RAX: ffffffff87596688 RBX: 0000000000000001 RCX: ffff88816f738000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc9000388f1c0 R08: ffff88816ecf302f R09: 1ffff1102dd9e605
R10: dffffc0000000000 R11: ffffed102dd9e606 R12: dffffc0000000000
R13: 0000000000000001 R14: 0000000000000000 R15: ffff8881be596000
FS:  00007f94438b96c0(0000) GS:ffff8882a8cca000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f94429eb840 CR3: 000000016e632000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
 atomic_notifier_call_chain+0xda/0x180 kernel/notifier.c:223
 call_fib_notifiers+0x31/0x60 net/core/fib_notifier.c:36
 call_fib6_multipath_entry_notifiers+0xf5/0x160 net/ipv6/ip6_fib.c:428
 ip6_route_multipath_add net/ipv6/route.c:5591 [inline]
 inet6_rtm_newroute+0x14f5/0x1a30 net/ipv6/route.c:5713
 rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7137
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2575
 netlink_unicast_kernel net/netlink/af_netlink.c:1338 [inline]
 netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1364
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800
 __sock_sendmsg net/socket.c:815 [inline]
 ____sys_sendmsg+0x54e/0x850 net/socket.c:2713
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2767
 __sys_sendmsg net/socket.c:2799 [inline]
 __do_sys_sendmsg net/socket.c:2804 [inline]
 __se_sys_sendmsg net/socket.c:2802 [inline]
 __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2802
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f944299e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f94438b9028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f9442c25fa0 RCX: 00007f944299e159
RDX: 0000000004000040 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 00007f9442a3506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9442c26038 R14: 00007f9442c25fa0 R15: 00007ffdb2cbb968
 </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

---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.

To test a fix for this bug, please reply with `#syz test`
(on a separate line) and attach the patch to the email.

Notes:
- The patch will be applied on top of the tested series (as an
  incremental fix).
- To test a new version of the whole series, please send it directly
  to syzbot@lists.linux.dev.
- Arguments like custom git repos and branches are not supported.