[moderation] [lvs?] KCSAN: data-race in ip_vs_add_service / ip_vs_out_hook

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cd2e103d57e5 Merge tag 'hardening-v6.16-rc1-fix1-take2' of..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=118bb970580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a8f90f190239c35c
dashboard link: https://syzkaller.appspot.com/bug?extid=1651b5234028c294c339
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [core...@netfilter.org da...@davemloft.net edum...@google.com ho...@verge.net.au j...@ssi.bg kad...@netfilter.org ku...@kernel.org linux-...@vger.kernel.org lvs-...@vger.kernel.org net...@vger.kernel.org netfilt...@vger.kernel.org pab...@redhat.com pa...@netfilter.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2dea1049fe27/disk-cd2e103d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9bbcc26e5a40/vmlinux-cd2e103d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fa17e0b8c8c0/bzImage-cd2e103d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1651b5...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in ip_vs_add_service / ip_vs_out_hook

write to 0xffff888117423804 of 4 bytes by task 13695 on cpu 1:
ip_vs_add_service+0xa18/0xa70 net/netfilter/ipvs/ip_vs_ctl.c:1487
do_ip_vs_set_ctl+0x6ec/0x8c0 net/netfilter/ipvs/ip_vs_ctl.c:2807
nf_setsockopt+0x199/0x1b0 net/netfilter/nf_sockopt.c:101
ip_setsockopt+0x102/0x110 net/ipv4/ip_sockglue.c:1424
udp_setsockopt+0x99/0xb0 net/ipv4/udp.c:3084
sock_common_setsockopt+0x69/0x80 net/core/sock.c:3944
do_sock_setsockopt net/socket.c:2296 [inline]
__sys_setsockopt+0x181/0x200 net/socket.c:2321
__do_sys_setsockopt net/socket.c:2327 [inline]
__se_sys_setsockopt net/socket.c:2324 [inline]
__x64_sys_setsockopt+0x64/0x80 net/socket.c:2324
x64_sys_call+0x2bd5/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:55
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888117423804 of 4 bytes by task 13687 on cpu 0:
ip_vs_out_hook+0x1c1/0x920 net/netfilter/ipvs/ip_vs_core.c:1356
nf_hook_entry_hookfn include/linux/netfilter.h:157 [inline]
nf_hook_slow+0x75/0x180 net/netfilter/core.c:623
nf_hook include/linux/netfilter.h:272 [inline]
__ip_local_out+0x2cb/0x2f0 net/ipv4/ip_output.c:118
ip_local_out net/ipv4/ip_output.c:127 [inline]
ip_send_skb+0x32/0x140 net/ipv4/ip_output.c:1502
udp_send_skb+0x6e3/0xa40 net/ipv4/udp.c:1197
udp_sendmsg+0x1050/0x13b0 net/ipv4/udp.c:1485
inet_sendmsg+0xac/0xd0 net/ipv4/af_inet.c:851
sock_sendmsg_nosec net/socket.c:712 [inline]
__sock_sendmsg+0x102/0x180 net/socket.c:727
____sys_sendmsg+0x345/0x4e0 net/socket.c:2566
___sys_sendmsg+0x17b/0x1d0 net/socket.c:2620
__sys_sendmmsg+0x178/0x300 net/socket.c:2709
__do_sys_sendmmsg net/socket.c:2736 [inline]
__se_sys_sendmmsg net/socket.c:2733 [inline]
__x64_sys_sendmmsg+0x57/0x70 net/socket.c:2733
x64_sys_call+0x2f2f/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:308
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 13687 Comm: syz.9.22917 Not tainted 6.15.0-syzkaller-10820-gcd2e103d57e5 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================
IPVS: dh: UDP 224.0.0.2:0 - no destination available


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