net: fix crash in tcp_nuke_addr()

When iterating through sockets we need to skip sockets in TIME_WAIT
state as they use lightweight structure inet_timewait_sock that does not
have sk_lock member, and if we try to lock them we'll crash thusly:

[   89.376383] BUG: spinlock lockup suspected on CPU#0, netd/431
[   89.382139]  lock: 0xffffffc039d05070, .magic: 66d30606, .owner: /-1682098992, .owner_cpu: 0
[   89.390598] CPU: 0 PID: 431 Comm: netd Tainted: G     U  W 3.18.0 #5
[   89.397389] Hardware name: Google Tegra210 Smaug Rev 1+ (DT)
[   89.403049] Call trace:
[   89.405501] [<ffffffc0002072b4>] dump_backtrace+0x0/0x10c
[   89.410918] [<ffffffc0002073d0>] show_stack+0x10/0x1c
[   89.415971] [<ffffffc000a88608>] dump_stack+0x74/0x94
[   89.421018] [<ffffffc000257e8c>] spin_dump+0x78/0x88
[   89.425984] [<ffffffc0002580d8>] do_raw_spin_lock+0xfc/0x158
[   89.431666] [<ffffffc000a90090>] _raw_spin_lock+0x34/0x44
[   89.437059] [<ffffffc0009509a8>] tcp_nuke_addr+0x1fc/0x29c
[   89.442548] [<ffffffc0009735f4>] devinet_ioctl+0x288/0x680
[   89.448053] [<ffffffc000975004>] inet_ioctl+0xc4/0xf4
[   89.453103] [<ffffffc0008baedc>] sock_do_ioctl+0x2c/0x5c
[   89.458408] [<ffffffc0008bbb54>] sock_ioctl+0x210/0x230
[   89.463633] [<ffffffc000317088>] do_vfs_ioctl+0x4ac/0x590
[   89.469049] [<ffffffc0003171c8>] SyS_ioctl+0x5c/0x88

(or with NULL pointer dereference if lockdep is still working).

Change-Id: I07c70d9a60b125b1070ff05c4eec27daee1a3e90
Signed-off-by: Dmitry Torokhov <dtor@google.com>

net/ipv4/tcp.c

@@ -3191,8 +3191,19 @@ int tcp_nuke_addr(struct net *net, struct sockaddr *addr)
 		sk_nulls_for_each(sk, node, &tcp_hashinfo.ehash[bucket].chain) {
 			struct inet_sock *inet = inet_sk(sk);
 
+			if (sk->sk_state == TCP_TIME_WAIT) {
+				/*
+				 * Sockets that are in TIME_WAIT state are
+				 * instances of lightweight inet_timewait_sock,
+				 * we should simply skip them (or we'll try to
+				 * access non-existing fields and crash).
+				 */
+				continue;
+			}
+
 			if (sysctl_ip_dynaddr && sk->sk_state == TCP_SYN_SENT)
 				continue;
+
 			if (sock_flag(sk, SOCK_DEAD))
 				continue;