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From: Kuniyuki Iwashima To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Willem de Bruijn Cc: Simon Horman , David Held , Kuniyuki Iwashima , Kuniyuki Iwashima , netdev@vger.kernel.org, syzbot+04905b8b3523856476c0@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" __udp4_lib_mcast_demux_lookup() and __udp4_lib_mcast_deliver() reads the number of sockets in the 1-tuple hash table chain locklessly. [0] Let's use READ_ONCE() and WRITE_ONCE() for hslot->count. [0]: BUG: KCSAN: data-race in __udp4_lib_mcast_deliver / udp_lib_unhash read-write to 0xffff88810194a9c8 of 4 bytes by task 15107 on cpu 0: udp_lib_unhash+0x1f4/0x3e0 net/ipv4/udp.c:2261 sk_common_release+0x7a/0x230 net/core/sock.c:3990 udp_lib_close+0x15/0x20 include/net/udp.h:324 inet_release+0xcd/0xf0 net/ipv4/af_inet.c:437 __sock_release net/socket.c:662 [inline] sock_close+0x6b/0x150 net/socket.c:1455 __fput+0x29b/0x650 fs/file_table.c:469 ____fput+0x1c/0x30 fs/file_table.c:497 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+0x1f4/0x6f0 kernel/entry/common.c:98 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline] do_syscall_64+0x249/0x370 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f read to 0xffff88810194a9c8 of 4 bytes by task 15111 on cpu 1: __udp4_lib_mcast_deliver+0x9a/0x790 net/ipv4/udp.c:2564 __udp4_lib_rcv+0x972/0x1250 net/ipv4/udp.c:2749 udp_rcv+0x4f/0x60 net/ipv4/udp.c:2936 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:584 [inline] ip_list_rcv_finish net/ipv4/ip_input.c:628 [inline] ip_sublist_rcv+0x415/0x6a0 net/ipv4/ip_input.c:644 ip_list_rcv+0x261/0x290 net/ipv4/ip_input.c:678 __netif_receive_skb_list_ptype net/core/dev.c:6207 [inline] __netif_receive_skb_list_core+0x4dc/0x500 net/core/dev.c:6254 __netif_receive_skb_list net/core/dev.c:6306 [inline] netif_receive_skb_list_internal+0x47d/0x5f0 net/core/dev.c:6397 netif_receive_skb_list+0x35/0x220 net/core/dev.c:6449 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:1397 bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4722 __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6246 __do_sys_bpf kernel/bpf/syscall.c:6341 [inline] __se_sys_bpf kernel/bpf/syscall.c:6339 [inline] __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6339 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/0x370 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: 1 UID: 0 PID: 15111 Comm: syz.6.4060 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026 Fixes: 2dc41cff7545 ("udp: Use hash2 for long hash1 chains in __udp*_lib_mcast_deliver.") Fixes: 63c6f81cdde5 ("udp: ipv4: do not waste time in __udp4_lib_mcast_demux_lookup") Reported-by: syzbot+04905b8b3523856476c0@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/69e97093.050a0220.24bfd3.0048.GAE@google.com/ Signed-off-by: Kuniyuki Iwashima --- net/ipv4/udp.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 0ac2bf4f8759..f7e6045f5985 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -323,7 +323,7 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum, sock_set_flag(sk, SOCK_RCU_FREE); sk_add_node_rcu(sk, &hslot->head); - hslot->count++; + WRITE_ONCE(hslot->count, hslot->count + 1); sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1); hslot2 = udp_hashslot2(udptable, udp_sk(sk)->udp_portaddr_hash); @@ -2200,7 +2200,7 @@ void udp_lib_unhash(struct sock *sk) if (rcu_access_pointer(sk->sk_reuseport_cb)) reuseport_detach_sock(sk); if (sk_del_node_init_rcu(sk)) { - hslot->count--; + WRITE_ONCE(hslot->count, hslot->count - 1); inet_sk(sk)->inet_num = 0; sock_prot_inuse_add(net, sk->sk_prot, -1); @@ -2471,7 +2471,7 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb, hash2_any = 0; hash2 = 0; hslot = udp_hashslot(udptable, net, hnum); - use_hash2 = hslot->count > 10; + use_hash2 = READ_ONCE(hslot->count) > 10; offset = offsetof(typeof(*sk), sk_node); if (use_hash2) { @@ -2703,7 +2703,7 @@ static struct sock *__udp4_lib_mcast_demux_lookup(struct net *net, hslot = &udptable->hash[slot]; /* Do not bother scanning a too big list */ - if (hslot->count > 10) + if (READ_ONCE(hslot->count) > 10) return NULL; result = NULL; -- 2.54.0.rc2.533.g4f5dca5207-goog