ib_srpt: Fix a use-after-free in __srpt_close_all_ch()

BUG: KASAN: use-after-free in srpt_set_enabled+0x1a9/0x1e0 [ib_srpt]
Read of size 4 at addr ffff8801269d23f8 by task check/29726

CPU: 4 PID: 29726 Comm: check Not tainted 4.18.0-rc2-dbg+ #4
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
Call Trace:
 dump_stack+0xa4/0xf5
 print_address_description+0x6f/0x270
 kasan_report+0x241/0x360
 __asan_load4+0x78/0x80
 srpt_set_enabled+0x1a9/0x1e0 [ib_srpt]
 srpt_tpg_enable_store+0xb8/0x120 [ib_srpt]
 configfs_write_file+0x14e/0x1d0 [configfs]
 __vfs_write+0xd2/0x3b0
 vfs_write+0x101/0x270
 ksys_write+0xab/0x120
 __x64_sys_write+0x43/0x50
 do_syscall_64+0x77/0x230
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f235cfe6154

Fixes: aaf45bd83eba ("IB/srpt: Detect session shutdown reliably")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/ulp/srpt/ib_srpt.c

@@ -1940,8 +1940,8 @@ static void __srpt_close_all_ch(struct srpt_port *sport)
 	list_for_each_entry(nexus, &sport->nexus_list, entry) {
 		list_for_each_entry(ch, &nexus->ch_list, list) {
 			if (srpt_disconnect_ch(ch) >= 0)
-				pr_info("Closing channel %s-%d because target %s_%d has been disabled\n",
-					ch->sess_name, ch->qp->qp_num,
+				pr_info("Closing channel %s because target %s_%d has been disabled\n",
+					ch->sess_name,
 					sport->sdev->device->name, sport->port);
 			srpt_close_ch(ch);
 		}