scsi: iscsi: Don't send data to unbound connection

If a faulty initiator fails to bind the socket to the iSCSI connection
before emitting a command, for instance, a subsequent send_pdu, it will
crash the kernel due to a null pointer dereference in sock_sendmsg(), as
shown in the log below.  This patch makes sure the bind succeeded before
trying to use the socket.

BUG: kernel NULL pointer dereference, address: 0000000000000018
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] SMP PTI
CPU: 3 PID: 7 Comm: kworker/u8:0 Not tainted 5.4.0-rc2.iscsi+ #13
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
[   24.158246] Workqueue: iscsi_q_0 iscsi_xmitworker
[   24.158883] RIP: 0010:apparmor_socket_sendmsg+0x5/0x20
[...]
[   24.161739] RSP: 0018:ffffab6440043ca0 EFLAGS: 00010282
[   24.162400] RAX: ffffffff891c1c00 RBX: ffffffff89d53968 RCX: 0000000000000001
[   24.163253] RDX: 0000000000000030 RSI: ffffab6440043d00 RDI: 0000000000000000
[   24.164104] RBP: 0000000000000030 R08: 0000000000000030 R09: 0000000000000030
[   24.165166] R10: ffffffff893e66a0 R11: 0000000000000018 R12: ffffab6440043d00
[   24.166038] R13: 0000000000000000 R14: 0000000000000000 R15: ffff9d5575a62e90
[   24.166919] FS:  0000000000000000(0000) GS:ffff9d557db80000(0000) knlGS:0000000000000000
[   24.167890] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   24.168587] CR2: 0000000000000018 CR3: 000000007a838000 CR4: 00000000000006e0
[   24.169451] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   24.170320] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   24.171214] Call Trace:
[   24.171537]  security_socket_sendmsg+0x3a/0x50
[   24.172079]  sock_sendmsg+0x16/0x60
[   24.172506]  iscsi_sw_tcp_xmit_segment+0x77/0x120
[   24.173076]  iscsi_sw_tcp_pdu_xmit+0x58/0x170
[   24.173604]  ? iscsi_dbg_trace+0x63/0x80
[   24.174087]  iscsi_tcp_task_xmit+0x101/0x280
[   24.174666]  iscsi_xmit_task+0x83/0x110
[   24.175206]  iscsi_xmitworker+0x57/0x380
[   24.175757]  ? __schedule+0x2a2/0x700
[   24.176273]  process_one_work+0x1b5/0x360
[   24.176837]  worker_thread+0x50/0x3c0
[   24.177353]  kthread+0xf9/0x130
[   24.177799]  ? process_one_work+0x360/0x360
[   24.178401]  ? kthread_park+0x90/0x90
[   24.178915]  ret_from_fork+0x35/0x40
[   24.179421] Modules linked in:
[   24.179856] CR2: 0000000000000018
[   24.180327] ---[ end trace b4b7674b6df5f480 ]---

Signed-off-by: Anatol Pomazau <anatol@google.com>
Co-developed-by: Frank Mayhar <fmayhar@google.com>
Signed-off-by: Frank Mayhar <fmayhar@google.com>
Co-developed-by: Bharath Ravi <rbharath@google.com>
Signed-off-by: Bharath Ravi <rbharath@google.com>
Co-developed-by: Khazhimsel Kumykov <khazhy@google.com>
Signed-off-by: Khazhimsel Kumykov <khazhy@google.com>
Co-developed-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/iscsi_tcp.c

@@ -369,8 +369,16 @@ static int iscsi_sw_tcp_pdu_xmit(struct iscsi_task *task)
 {
 	struct iscsi_conn *conn = task->conn;
 	unsigned int noreclaim_flag;
+	struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
+	struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
 	int rc = 0;
 
+	if (!tcp_sw_conn->sock) {
+		iscsi_conn_printk(KERN_ERR, conn,
+				  "Transport not bound to socket!\n");
+		return -EINVAL;
+	}
+
 	noreclaim_flag = memalloc_noreclaim_save();
 
 	while (iscsi_sw_tcp_xmit_qlen(conn)) {