udp: annotate data races around unix_sk(sk)->gso_size

Accesses to unix_sk(sk)->gso_size are lockless.
Add READ_ONCE()/WRITE_ONCE() around them.

BUG: KCSAN: data-race in udp_lib_setsockopt / udpv6_sendmsg

write to 0xffff88812d78f47c of 2 bytes by task 10849 on cpu 1:
 udp_lib_setsockopt+0x3b3/0x710 net/ipv4/udp.c:2696
 udpv6_setsockopt+0x63/0x90 net/ipv6/udp.c:1630
 sock_common_setsockopt+0x5d/0x70 net/core/sock.c:3265
 __sys_setsockopt+0x18f/0x200 net/socket.c:2104
 __do_sys_setsockopt net/socket.c:2115 [inline]
 __se_sys_setsockopt net/socket.c:2112 [inline]
 __x64_sys_setsockopt+0x62/0x70 net/socket.c:2112
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88812d78f47c of 2 bytes by task 10852 on cpu 0:
 udpv6_sendmsg+0x161/0x16b0 net/ipv6/udp.c:1299
 inet6_sendmsg+0x5f/0x80 net/ipv6/af_inet6.c:642
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg net/socket.c:674 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2337
 ___sys_sendmsg net/socket.c:2391 [inline]
 __sys_sendmmsg+0x315/0x4b0 net/socket.c:2477
 __do_sys_sendmmsg net/socket.c:2506 [inline]
 __se_sys_sendmmsg net/socket.c:2503 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2503
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000 -> 0x0005

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10852 Comm: syz-executor.0 Not tainted 5.13.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Fixes: bec1f6f ("udp: generate gso with UDP_SEGMENT")
Signed-off-by: Eric Dumazet <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Reported-by: syzbot <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: edumazet

net/ipv4/udp.c

@@ -1102,7 +1102,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	}
 
 	ipcm_init_sk(&ipc, inet);
-	ipc.gso_size = up->gso_size;
+	ipc.gso_size = READ_ONCE(up->gso_size);
 
 	if (msg->msg_controllen) {
 		err = udp_cmsg_send(sk, msg, &ipc.gso_size);
@@ -2695,7 +2695,7 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
 	case UDP_SEGMENT:
 		if (val < 0 || val > USHRT_MAX)
 			return -EINVAL;
-		up->gso_size = val;
+		WRITE_ONCE(up->gso_size, val);
 		break;
 
 	case UDP_GRO:
@@ -2790,7 +2790,7 @@ int udp_lib_getsockopt(struct sock *sk, int level, int optname,
 		break;
 
 	case UDP_SEGMENT:
-		val = up->gso_size;
+		val = READ_ONCE(up->gso_size);
 		break;
 
 	case UDP_GRO:

net/ipv6/udp.c

@@ -1296,7 +1296,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);
 
 	ipcm6_init(&ipc6);
-	ipc6.gso_size = up->gso_size;
+	ipc6.gso_size = READ_ONCE(up->gso_size);
 	ipc6.sockc.tsflags = sk->sk_tsflags;
 	ipc6.sockc.mark = sk->sk_mark;