net/smc: fix general protection fault in __smc_diag_dump

Syzbot reported a general protection fault:

  CPU: 0 UID: 0 PID: 5830 Comm: syz-executor600 Not tainted 6.14.0-rc4-syzkaller-00090-gdd83757f6e68 #0
  RIP: 0010:smc_diag_msg_common_fill net/smc/smc_diag.c:44 [inline]
  RIP: 0010:__smc_diag_dump.constprop.0+0x3de/0x23d0 net/smc/smc_diag.c:89
  Call Trace:
   <TASK>
   smc_diag_dump_proto+0x26d/0x420 net/smc/smc_diag.c:217
   smc_diag_dump+0x84/0x90 net/smc/smc_diag.c:236
   netlink_dump+0x53c/0xd00 net/netlink/af_netlink.c:2318
   __netlink_dump_start+0x6ca/0x970 net/netlink/af_netlink.c:2433
   netlink_dump_start include/linux/netlink.h:340 [inline]
   smc_diag_handler_dump+0x1fb/0x240 net/smc/smc_diag.c:251
   __sock_diag_cmd net/core/sock_diag.c:249 [inline]
   sock_diag_rcv_msg+0x437/0x790 net/core/sock_diag.c:287
   netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2543
   netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]
   netlink_unicast+0x53c/0x7f0 net/netlink/af_netlink.c:1348
   netlink_sendmsg+0x8b8/0xd70 net/netlink/af_netlink.c:1892
   sock_sendmsg_nosec net/socket.c:718 [inline]
   __sock_sendmsg net/socket.c:733 [inline]
   ____sys_sendmsg+0xaaf/0xc90 net/socket.c:2573
   ___sys_sendmsg+0x135/0x1e0 net/socket.c:2627
   __sys_sendmsg+0x16e/0x220 net/socket.c:2659
   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
   do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>

When create smc socket, smc_inet_init_sock() first add sk to the smc_hash
by smc_hash_sk(), then create smc->clcsock. it is possible that, after
smc_diag_dump_proto() traverses the smc_hash, smc->clcsock is not created
when the function visit it.

The process like this:

  (CPU1)                         | (CPU2)
  inet6_create()                 |
    smc_inet_init_sock()         |
      smc_sk_init()              |
        smc_hash_sk()            |
          head = &smc_hash->ht;  |
          sk_add_node(sk, head); |
                                 | smc_diag_dump_proto
                                 |   head = &smc_hash->ht;
                                 |     sk_for_each(sk, head)
                                 |       __smc_diag_dump()
                                 |         visit smc->clcsock
      smc_create_clcsk()         |
          set smc->clcsock       |

Fix this by initialize smc->clcsock to NULL before add sk to smc_hash in
smc_sk_init().

Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=271fed3ed6f24600c364
Fixes: f16a7dd ("smc: netlink interface for SMC sockets")
Signed-off-by: Wang Liang <[email protected]>
Signed-off-by: NipaLocal <nipa@local>

Author: Wang Liang

net/smc/af_smc.c

@@ -371,6 +371,7 @@ void smc_sk_init(struct net *net, struct sock *sk, int protocol)
 	sk->sk_protocol = protocol;
 	WRITE_ONCE(sk->sk_sndbuf, 2 * READ_ONCE(net->smc.sysctl_wmem));
 	WRITE_ONCE(sk->sk_rcvbuf, 2 * READ_ONCE(net->smc.sysctl_rmem));
+	smc->clcsock = NULL;
 	INIT_WORK(&smc->tcp_listen_work, smc_tcp_listen_work);
 	INIT_WORK(&smc->connect_work, smc_connect_work);
 	INIT_DELAYED_WORK(&smc->conn.tx_work, smc_tx_work);