tipc: Fix use-after-free in tipc_conn_close().

In the Linux kernel, the following vulnerability has been resolved:

tipc: Fix use-after-free in tipc_conn_close().

syzbot reported a null-ptr-deref in tipc_conn_close() during netns

dismantle. [0]

tipc_topsrv_stop() iterates tipc_net(net)->topsrv->conn_idr and calls

tipc_conn_close() for each tipc_conn.

The problem is that tipc_conn_close() is called after releasing the

IDR lock.

At the same time, there might be tipc_conn_recv_work() running and it

could call tipc_conn_close() for the same tipc_conn and release its

last ->kref.

Once we release the IDR lock in tipc_topsrv_stop(), there is no

guarantee that the tipc_conn is alive.

Let's hold the ref before releasing the lock and put the ref after

tipc_conn_close() in tipc_topsrv_stop().

[0]:

BUG: KASAN: use-after-free in tipc_conn_close+0x122/0x140 net/tipc/topsrv.c:165

Read of size 8 at addr ffff888099305a08 by task kworker/u4:3/435

CPU: 0 PID: 435 Comm: kworker/u4:3 Not tainted 4.19.204-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Workqueue: netns cleanup_net

Call Trace:

__dump_stack lib/dump_stack.c:77 [inline]

dump_stack+0x1fc/0x2ef lib/dump_stack.c:118

print_address_description.cold+0x54/0x219 mm/kasan/report.c:256

kasan_report_error.cold+0x8a/0x1b9 mm/kasan/report.c:354

kasan_report mm/kasan/report.c:412 [inline]

__asan_report_load8_noabort+0x88/0x90 mm/kasan/report.c:433

tipc_conn_close+0x122/0x140 net/tipc/topsrv.c:165

tipc_topsrv_stop net/tipc/topsrv.c:701 [inline]

tipc_topsrv_exit_net+0x27b/0x5c0 net/tipc/topsrv.c:722

ops_exit_list+0xa5/0x150 net/core/net_namespace.c:153

cleanup_net+0x3b4/0x8b0 net/core/net_namespace.c:553

process_one_work+0x864/0x1570 kernel/workqueue.c:2153

worker_thread+0x64c/0x1130 kernel/workqueue.c:2296

kthread+0x33f/0x460 kernel/kthread.c:259

ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Allocated by task 23:

kmem_cache_alloc_trace+0x12f/0x380 mm/slab.c:3625

kmalloc include/linux/slab.h:515 [inline]

kzalloc include/linux/slab.h:709 [inline]

tipc_conn_alloc+0x43/0x4f0 net/tipc/topsrv.c:192

tipc_topsrv_accept+0x1b5/0x280 net/tipc/topsrv.c:470

process_one_work+0x864/0x1570 kernel/workqueue.c:2153

worker_thread+0x64c/0x1130 kernel/workqueue.c:2296

kthread+0x33f/0x460 kernel/kthread.c:259

ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Freed by task 23:

__cache_free mm/slab.c:3503 [inline]

kfree+0xcc/0x210 mm/slab.c:3822

tipc_conn_kref_release net/tipc/topsrv.c:150 [inline]

kref_put include/linux/kref.h:70 [inline]

conn_put+0x2cd/0x3a0 net/tipc/topsrv.c:155

process_one_work+0x864/0x1570 kernel/workqueue.c:2153

worker_thread+0x64c/0x1130 kernel/workqueue.c:2296

kthread+0x33f/0x460 kernel/kthread.c:259

ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

The buggy address belongs to the object at ffff888099305a00

which belongs to the cache kmalloc-512 of size 512

The buggy address is located 8 bytes inside of

512-byte region [ffff888099305a00, ffff888099305c00)

The buggy address belongs to the page:

page:ffffea000264c140 count:1 mapcount:0 mapping:ffff88813bff0940 index:0x0

flags: 0xfff00000000100(slab)

raw: 00fff00000000100 ffffea00028b6b88 ffffea0002cd2b08 ffff88813bff0940

raw: 0000000000000000 ffff888099305000 0000000100000006 0000000000000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff888099305900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

ffff888099305980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

>ffff888099305a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

^

ffff888099305a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

ffff888099305b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb