[PATCH v1 bpf/net 1/6] sockmap: Annotate sk->sk_data_ready() for UDP.

[Kuniyuki Iwashima <kuniyu@google.com>]

syzbot reported data race of sk->sk_data_ready(). [0]

UDP fast path does not hold bh_lock_sock(), instead
spin_lock_bh(&sk->sk_receive_queue.lock) is used.

Let's use WRITE_ONCE() and READ_ONCE() for sk->sk_data_ready().

Another option is to hold sk->sk_receive_queue.lock in
sock_map_sk_acquire() if sk_is_udp() is true, but this is
overkill and also does not work for sk->sk_write_space().

[0]:
BUG: KCSAN: data-race in __udp_enqueue_schedule_skb / sk_psock_drop

write to 0xffff88811d063048 of 8 bytes by task 23114 on cpu 0:
 sk_psock_stop_verdict net/core/skmsg.c:1287 [inline]
 sk_psock_drop+0x12f/0x270 net/core/skmsg.c:873
 sk_psock_put include/linux/skmsg.h:473 [inline]
 sock_map_unref+0x2a5/0x300 net/core/sock_map.c:185
 __sock_map_delete net/core/sock_map.c:426 [inline]
 sock_map_delete_from_link net/core/sock_map.c:439 [inline]
 sock_map_unlink net/core/sock_map.c:1608 [inline]
 sock_map_remove_links+0x228/0x340 net/core/sock_map.c:1623
 sock_map_close+0xa1/0x340 net/core/sock_map.c:1684
 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:468
 ____fput+0x1c/0x30 fs/file_table.c:496
 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:44 [inline]
 exit_to_user_mode_loop+0x1f7/0x6f0 kernel/entry/common.c:75
 __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_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x1d3/0x2a0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811d063048 of 8 bytes by task 23117 on cpu 1:
 __udp_enqueue_schedule_skb+0x6c1/0x840 net/ipv4/udp.c:1789
 __udp_queue_rcv_skb net/ipv4/udp.c:2346 [inline]
 udp_queue_rcv_one_skb+0x709/0xc20 net/ipv4/udp.c:2475
 udp_queue_rcv_skb+0x20e/0x2b0 net/ipv4/udp.c:2493
 __udp4_lib_mcast_deliver+0x6e8/0x790 net/ipv4/udp.c:2585
 __udp4_lib_rcv+0x96f/0x1260 net/ipv4/udp.c:2724
 udp_rcv+0x4f/0x60 net/ipv4/udp.c:2911
 ip_protocol_deliver_rcu+0x3f9/0x780 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:474 [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+0x42b/0x6d0 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:6195 [inline]
 __netif_receive_skb_list_core+0x4dc/0x500 net/core/dev.c:6242
 __netif_receive_skb_list net/core/dev.c:6294 [inline]
 netif_receive_skb_list_internal+0x47d/0x5f0 net/core/dev.c:6385
 netif_receive_skb_list+0x31/0x1f0 net/core/dev.c:6437
 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:1396
 bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4703
 __sys_bpf+0x4c0/0x7b0 kernel/bpf/syscall.c:6182
 __do_sys_bpf kernel/bpf/syscall.c:6274 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6272 [inline]
 __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6272
 x64_sys_call+0x28e1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:322
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffffffff847b24d0 -> 0xffffffff84673410

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 23117 Comm: syz.8.5085 Tainted: G        W           syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025

Fixes: 7b98cd42b049 ("bpf: sockmap: Add UDP support")
Reported-by: syzbot+113cea56c13a8a1e95ab@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/69922ac9.a70a0220.2c38d7.00e1.GAE@google.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/core/skmsg.c | 4 ++--
 net/ipv4/udp.c   | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index ddde93dd8bc6..75fa94217e1e 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -1296,7 +1296,7 @@ void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock)
 		return;
 
 	psock->saved_data_ready = sk->sk_data_ready;
-	sk->sk_data_ready = sk_psock_verdict_data_ready;
+	WRITE_ONCE(sk->sk_data_ready, sk_psock_verdict_data_ready);
 	sk->sk_write_space = sk_psock_write_space;
 }
 
@@ -1308,6 +1308,6 @@ void sk_psock_stop_verdict(struct sock *sk, struct sk_psock *psock)
 	if (!psock->saved_data_ready)
 		return;
 
-	sk->sk_data_ready = psock->saved_data_ready;
+	WRITE_ONCE(sk->sk_data_ready, psock->saved_data_ready);
 	psock->saved_data_ready = NULL;
 }
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index b96e47f1c8a2..422c96fea249 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1787,7 +1787,7 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
 		 * using prepare_to_wait_exclusive().
 		 */
 		while (nb) {
-			INDIRECT_CALL_1(sk->sk_data_ready,
+			INDIRECT_CALL_1(READ_ONCE(sk->sk_data_ready),
 					sock_def_readable, sk);
 			nb--;
 		}
-- 
2.53.0.310.g728cabbaf7-goog