[moderation] [net?] KCSAN: data-race in __udp4_lib_mcast_deliver / udp_lib_unhash (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e1914add2799 Merge tag 'for-linus' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17c220ec580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2e40c0f41e01837e
dashboard link: https://syzkaller.appspot.com/bug?extid=2ef428d898f744a8416c
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [da...@davemloft.net edum...@google.com ho...@kernel.org ku...@kernel.org linux-...@vger.kernel.org net...@vger.kernel.org pab...@redhat.com willemdebr...@gmail.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/03233d3d6513/disk-e1914add.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e07e87ff26ae/vmlinux-e1914add.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b4aac9596709/bzImage-e1914add.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2ef428...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __udp4_lib_mcast_deliver / udp_lib_unhash

read-write to 0xffff8881018c5058 of 4 bytes by task 19156 on cpu 1:
udp_lib_unhash+0x1b1/0x3a0 net/ipv4/udp.c:2203
sk_common_release+0x7a/0x230 net/core/sock.c:4006
udp_lib_close+0x15/0x20 include/net/udp.h:322
inet_release+0xcd/0xf0 net/ipv4/af_inet.c:442
inet6_release+0x3e/0x60 net/ipv6/af_inet6.c:472
__sock_release net/socket.c:722 [inline]
sock_close+0x6b/0x150 net/socket.c:1514
__fput+0x29b/0x630 fs/file_table.c:510
____fput+0x1c/0x30 fs/file_table.c:538
task_work_run+0x130/0x1a0 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
exit_to_user_mode_loop+0x211/0x820 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
do_syscall_64+0x232/0x3b0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881018c5058 of 4 bytes by task 19147 on cpu 0:
__udp4_lib_mcast_deliver+0x12f/0x690 net/ipv4/udp.c:2474
udp_rcv+0x79b/0xe80 net/ipv4/udp.c:2639
ip_protocol_deliver_rcu+0x3f7/0x790 net/ipv4/ip_input.c:207
ip_local_deliver_finish+0x1fc/0x2f0 net/ipv4/ip_input.c:241
NF_HOOK include/linux/netfilter.h:318 [inline]
ip_local_deliver+0xe8/0x1e0 net/ipv4/ip_input.c:262
dst_input include/net/dst.h:480 [inline]
ip_sublist_rcv_finish net/ipv4/ip_input.c:623 [inline]
ip_list_rcv_finish net/ipv4/ip_input.c:667 [inline]
ip_sublist_rcv+0x415/0x6a0 net/ipv4/ip_input.c:683
ip_list_rcv+0x261/0x290 net/ipv4/ip_input.c:717
__netif_receive_skb_list_ptype net/core/dev.c:6245 [inline]
__netif_receive_skb_list_core+0x4dc/0x500 net/core/dev.c:6292
__netif_receive_skb_list net/core/dev.c:6344 [inline]
netif_receive_skb_list_internal+0x47d/0x5f0 net/core/dev.c:6435
netif_receive_skb_list+0x33/0x1c0 net/core/dev.c:6487
xdp_recv_frames net/bpf/test_run.c:269 [inline]
xdp_test_run_batch net/bpf/test_run.c:350 [inline]
bpf_test_run_xdp_live+0x104c/0x1360 net/bpf/test_run.c:379
bpf_prog_test_run_xdp+0x57b/0xa10 net/bpf/test_run.c:1430
bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4742
__sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6266
__do_sys_bpf kernel/bpf/syscall.c:6361 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6359 [inline]
__x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6359
x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000001 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 19147 Comm: syz.5.3498 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================


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