af_packet: Fix data-races of pkt_sk(sk)->num.

syzkaller found a data race of pkt_sk(sk)->num.

The value is changed under lock_sock() and po->bind_lock, so we
need READ_ONCE() to access pkt_sk(sk)->num without these locks in
packet_bind_spkt(), packet_bind(), and sk_diag_fill().

Note that WRITE_ONCE() is already added by commit c7d2ef5d
("net/packet: annotate accesses to po->bind").

BUG: KCSAN: data-race in packet_bind / packet_do_bind

write (marked) to 0xffff88802ffd1cee of 2 bytes by task 7322 on cpu 0:
 packet_do_bind+0x446/0x640 net/packet/af_packet.c:3236
 packet_bind+0x99/0xe0 net/packet/af_packet.c:3321
 __sys_bind+0x19b/0x1e0 net/socket.c:1803
 __do_sys_bind net/socket.c:1814 [inline]
 __se_sys_bind net/socket.c:1812 [inline]
 __x64_sys_bind+0x40/0x50 net/socket.c:1812
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3b/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x72/0xdc

read to 0xffff88802ffd1cee of 2 bytes by task 7318 on cpu 1:
 packet_bind+0xbf/0xe0 net/packet/af_packet.c:3322
 __sys_bind+0x19b/0x1e0 net/socket.c:1803
 __do_sys_bind net/socket.c:1814 [inline]
 __se_sys_bind net/socket.c:1812 [inline]
 __x64_sys_bind+0x40/0x50 net/socket.c:1812
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3b/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x72/0xdc

value changed: 0x0300 -> 0x0000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7318 Comm: syz-executor.4 Not tainted 6.3.0-13380-g7fddb5b5300c #4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014

Fixes: 96ec6327 ("packet: Diag core and basic socket info dumping")
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by: syzkaller <syzkaller@googlegroups.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20230524232934.50950-1-kuniyu@amazon.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/packet/af_packet.c

@@ -3299,7 +3299,7 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr,
 	memcpy(name, uaddr->sa_data, sizeof(uaddr->sa_data_min));
 	name[sizeof(uaddr->sa_data_min)] = 0;
 
-	return packet_do_bind(sk, name, 0, pkt_sk(sk)->num);
+	return packet_do_bind(sk, name, 0, READ_ONCE(pkt_sk(sk)->num));
 }
 
 static int packet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
@@ -3317,7 +3317,7 @@ static int packet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len
 		return -EINVAL;
 
 	return packet_do_bind(sk, NULL, sll->sll_ifindex,
-			      sll->sll_protocol ? : pkt_sk(sk)->num);
+			      sll->sll_protocol ? : READ_ONCE(pkt_sk(sk)->num));
 }
 
 static struct proto packet_proto = {

net/packet/diag.c

@@ -143,7 +143,7 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb,
 	rp = nlmsg_data(nlh);
 	rp->pdiag_family = AF_PACKET;
 	rp->pdiag_type = sk->sk_type;
-	rp->pdiag_num = ntohs(po->num);
+	rp->pdiag_num = ntohs(READ_ONCE(po->num));
 	rp->pdiag_ino = sk_ino;
 	sock_diag_save_cookie(sk, rp->pdiag_cookie);