net: rds: force to destroy connection if t_sock is NULL in rds_tcp_kill_sock().

When it is to cleanup net namespace, rds_tcp_exit_net() will call
rds_tcp_kill_sock(), if t_sock is NULL, it will not call
rds_conn_destroy(), rds_conn_path_destroy() and rds_tcp_conn_free() to free
connection, and the worker cp_conn_w is not stopped, afterwards the net is freed in
net_drop_ns(); While cp_conn_w rds_connect_worker() will call rds_tcp_conn_path_connect()
and reference 'net' which has already been freed.

In rds_tcp_conn_path_connect(), rds_tcp_set_callbacks() will set t_sock = sock before
sock->ops->connect, but if connect() is failed, it will call
rds_tcp_restore_callbacks() and set t_sock = NULL, if connect is always
failed, rds_connect_worker() will try to reconnect all the time, so
rds_tcp_kill_sock() will never to cancel worker cp_conn_w and free the
connections.

Therefore, the condition !tc->t_sock is not needed if it is going to do
cleanup_net->rds_tcp_exit_net->rds_tcp_kill_sock, because tc->t_sock is always
NULL, and there is on other path to cancel cp_conn_w and free
connection. So this patch is to fix this.

rds_tcp_kill_sock():
...
if (net != c_net || !tc->t_sock)
...
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>

==================================================================
BUG: KASAN: use-after-free in inet_create+0xbcc/0xd28
net/ipv4/af_inet.c:340
Read of size 4 at addr ffff8003496a4684 by task kworker/u8:4/3721

CPU: 3 PID: 3721 Comm: kworker/u8:4 Not tainted 5.1.0 #11
Hardware name: linux,dummy-virt (DT)
Workqueue: krdsd rds_connect_worker
Call trace:
 dump_backtrace+0x0/0x3c0 arch/arm64/kernel/time.c:53
 show_stack+0x28/0x38 arch/arm64/kernel/traps.c:152
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x120/0x188 lib/dump_stack.c:113
 print_address_description+0x68/0x278 mm/kasan/report.c:253
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x21c/0x348 mm/kasan/report.c:409
 __asan_report_load4_noabort+0x30/0x40 mm/kasan/report.c:429
 inet_create+0xbcc/0xd28 net/ipv4/af_inet.c:340
 __sock_create+0x4f8/0x770 net/socket.c:1276
 sock_create_kern+0x50/0x68 net/socket.c:1322
 rds_tcp_conn_path_connect+0x2b4/0x690 net/rds/tcp_connect.c:114
 rds_connect_worker+0x108/0x1d0 net/rds/threads.c:175
 process_one_work+0x6e8/0x1700 kernel/workqueue.c:2153
 worker_thread+0x3b0/0xdd0 kernel/workqueue.c:2296
 kthread+0x2f0/0x378 kernel/kthread.c:255
 ret_from_fork+0x10/0x18 arch/arm64/kernel/entry.S:1117

Allocated by task 687:
 save_stack mm/kasan/kasan.c:448 [inline]
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc+0xd4/0x180 mm/kasan/kasan.c:553
 kasan_slab_alloc+0x14/0x20 mm/kasan/kasan.c:490
 slab_post_alloc_hook mm/slab.h:444 [inline]
 slab_alloc_node mm/slub.c:2705 [inline]
 slab_alloc mm/slub.c:2713 [inline]
 kmem_cache_alloc+0x14c/0x388 mm/slub.c:2718
 kmem_cache_zalloc include/linux/slab.h:697 [inline]
 net_alloc net/core/net_namespace.c:384 [inline]
 copy_net_ns+0xc4/0x2d0 net/core/net_namespace.c:424
 create_new_namespaces+0x300/0x658 kernel/nsproxy.c:107
 unshare_nsproxy_namespaces+0xa0/0x198 kernel/nsproxy.c:206
 ksys_unshare+0x340/0x628 kernel/fork.c:2577
 __do_sys_unshare kernel/fork.c:2645 [inline]
 __se_sys_unshare kernel/fork.c:2643 [inline]
 __arm64_sys_unshare+0x38/0x58 kernel/fork.c:2643
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:47 [inline]
 el0_svc_common+0x168/0x390 arch/arm64/kernel/syscall.c:83
 el0_svc_handler+0x60/0xd0 arch/arm64/kernel/syscall.c:129
 el0_svc+0x8/0xc arch/arm64/kernel/entry.S:960

Freed by task 264:
 save_stack mm/kasan/kasan.c:448 [inline]
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0x114/0x220 mm/kasan/kasan.c:521
 kasan_slab_free+0x10/0x18 mm/kasan/kasan.c:528
 slab_free_hook mm/slub.c:1370 [inline]
 slab_free_freelist_hook mm/slub.c:1397 [inline]
 slab_free mm/slub.c:2952 [inline]
 kmem_cache_free+0xb8/0x3a8 mm/slub.c:2968
 net_free net/core/net_namespace.c:400 [inline]
 net_drop_ns.part.6+0x78/0x90 net/core/net_namespace.c:407
 net_drop_ns net/core/net_namespace.c:406 [inline]
 cleanup_net+0x53c/0x6d8 net/core/net_namespace.c:569
 process_one_work+0x6e8/0x1700 kernel/workqueue.c:2153
 worker_thread+0x3b0/0xdd0 kernel/workqueue.c:2296
 kthread+0x2f0/0x378 kernel/kthread.c:255
 ret_from_fork+0x10/0x18 arch/arm64/kernel/entry.S:1117

The buggy address belongs to the object at ffff8003496a3f80
 which belongs to the cache net_namespace of size 7872
The buggy address is located 1796 bytes inside of
 7872-byte region [ffff8003496a3f80, ffff8003496a5e40)
The buggy address belongs to the page:
page:ffff7e000d25a800 count:1 mapcount:0 mapping:ffff80036ce4b000
index:0x0 compound_mapcount: 0
flags: 0xffffe0000008100(slab|head)
raw: 0ffffe0000008100 dead000000000100 dead000000000200 ffff80036ce4b000
raw: 0000000000000000 0000000080040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8003496a4580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8003496a4600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8003496a4680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8003496a4700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8003496a4780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Fixes: 467fa15356ac("RDS-TCP: Support multiple RDS-TCP listen endpoints, one per netns.")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Mao Wenan <maowenan@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
