This commit fixes several use-after-free that caused by function
nfc_llcp_find_local(). For example, one UAF can happen when below buggy
time window occurs.

// nfc_genl_llc_get_params   | // nfc_unregister_device
                             |
dev = nfc_get_device(idx);   | device_lock(...)
if (!dev)                    | dev->shutting_down = true;
    return -ENODEV;          | device_unlock(...);
                             |
device_lock(...);            |   // nfc_llcp_unregister_device
                             |   nfc_llcp_find_local()
nfc_llcp_find_local(...);    |
                             |   local_cleanup()
if (!local) {                |
    rc = -ENODEV;            |     // nfc_llcp_local_put
    goto exit;               |     kref_put(.., local_release)
}                            |
                             |       // local_release
                             |       list_del(&local->list)
  // nfc_genl_send_params    |       kfree()
  local->dev->idx !!!UAF!!!  |
                             |

and the crash trace for the one of the discussed UAF like:

BUG: KASAN: slab-use-after-free in nfc_genl_llc_get_params+0x72f/0x780  net/nfc/netlink.c:1045
Read of size 8 at addr ffff888105b0e410 by task 20114

Call Trace:
 <TASK>
 __dump_stack  lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x72/0xa0  lib/dump_stack.c:106
 print_address_description  mm/kasan/report.c:319 [inline]
 print_report+0xcc/0x620  mm/kasan/report.c:430
 kasan_report+0xb2/0xe0  mm/kasan/report.c:536
 nfc_genl_send_params  net/nfc/netlink.c:999 [inline]
 nfc_genl_llc_get_params+0x72f/0x780  net/nfc/netlink.c:1045
 genl_family_rcv_msg_doit.isra.0+0x1ee/0x2e0  net/netlink/genetlink.c:968
 genl_family_rcv_msg  net/netlink/genetlink.c:1048 [inline]
 genl_rcv_msg+0x503/0x7d0  net/netlink/genetlink.c:1065
 netlink_rcv_skb+0x161/0x430  net/netlink/af_netlink.c:2548
 genl_rcv+0x28/0x40  net/netlink/genetlink.c:1076
 netlink_unicast_kernel  net/netlink/af_netlink.c:1339 [inline]
 netlink_unicast+0x644/0x900  net/netlink/af_netlink.c:1365
 netlink_sendmsg+0x934/0xe70  net/netlink/af_netlink.c:1913
 sock_sendmsg_nosec  net/socket.c:724 [inline]
 sock_sendmsg+0x1b6/0x200  net/socket.c:747
 ____sys_sendmsg+0x6e9/0x890  net/socket.c:2501
 ___sys_sendmsg+0x110/0x1b0  net/socket.c:2555
 __sys_sendmsg+0xf7/0x1d0  net/socket.c:2584
 do_syscall_x64  arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3f/0x90  arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x72/0xdc
RIP: 0033:0x7f34640a2389
RSP: 002b:00007f3463415168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f34641c1f80 RCX: 00007f34640a2389
RDX: 0000000000000000 RSI: 0000000020000240 RDI: 0000000000000006
RBP: 00007f34640ed493 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffe38449ecf R14: 00007f3463415300 R15: 0000000000022000
 </TASK>

Allocated by task 20116:
 kasan_save_stack+0x22/0x50  mm/kasan/common.c:45
 kasan_set_track+0x25/0x30  mm/kasan/common.c:52
 ____kasan_kmalloc  mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x7f/0x90  mm/kasan/common.c:383
 kmalloc  include/linux/slab.h:580 [inline]
 kzalloc  include/linux/slab.h:720 [inline]
 nfc_llcp_register_device+0x49/0xa40  net/nfc/llcp_core.c:1567
 nfc_register_device+0x61/0x260  net/nfc/core.c:1124
 nci_register_device+0x776/0xb20  net/nfc/nci/core.c:1257
 virtual_ncidev_open+0x147/0x230  drivers/nfc/virtual_ncidev.c:148
 misc_open+0x379/0x4a0  drivers/char/misc.c:165
 chrdev_open+0x26c/0x780  fs/char_dev.c:414
 do_dentry_open+0x6c4/0x12a0  fs/open.c:920
 do_open  fs/namei.c:3560 [inline]
 path_openat+0x24fe/0x37e0  fs/namei.c:3715
 do_filp_open+0x1ba/0x410  fs/namei.c:3742
 do_sys_openat2+0x171/0x4c0  fs/open.c:1356
 do_sys_open  fs/open.c:1372 [inline]
 __do_sys_openat  fs/open.c:1388 [inline]
 __se_sys_openat  fs/open.c:1383 [inline]
 __x64_sys_openat+0x143/0x200  fs/open.c:1383
 do_syscall_x64  arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3f/0x90  arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x72/0xdc

Freed by task 20115:
 kasan_save_stack+0x22/0x50  mm/kasan/common.c:45
 kasan_set_track+0x25/0x30  mm/kasan/common.c:52
 kasan_save_free_info+0x2e/0x50  mm/kasan/generic.c:521
 ____kasan_slab_free  mm/kasan/common.c:236 [inline]
 ____kasan_slab_free  mm/kasan/common.c:200 [inline]
 __kasan_slab_free+0x10a/0x190  mm/kasan/common.c:244
 kasan_slab_free  include/linux/kasan.h:162 [inline]
 slab_free_hook  mm/slub.c:1781 [inline]
 slab_free_freelist_hook  mm/slub.c:1807 [inline]
 slab_free  mm/slub.c:3787 [inline]
 __kmem_cache_free+0x7a/0x190  mm/slub.c:3800
 local_release  net/nfc/llcp_core.c:174 [inline]
 kref_put  include/linux/kref.h:65 [inline]
 nfc_llcp_local_put  net/nfc/llcp_core.c:182 [inline]
 nfc_llcp_local_put  net/nfc/llcp_core.c:177 [inline]
 nfc_llcp_unregister_device+0x206/0x290  net/nfc/llcp_core.c:1620
 nfc_unregister_device+0x160/0x1d0  net/nfc/core.c:1179
 virtual_ncidev_close+0x52/0xa0  drivers/nfc/virtual_ncidev.c:163
 __fput+0x252/0xa20  fs/file_table.c:321
 task_work_run+0x174/0x270  kernel/task_work.c:179
 resume_user_mode_work  include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop  kernel/entry/common.c:171 [inline]
 exit_to_user_mode_prepare+0x108/0x110  kernel/entry/common.c:204
 __syscall_exit_to_user_mode_work  kernel/entry/common.c:286 [inline]
 syscall_exit_to_user_mode+0x21/0x50  kernel/entry/common.c:297
 do_syscall_64+0x4c/0x90  arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x72/0xdc

Last potentially related work creation:
 kasan_save_stack+0x22/0x50  mm/kasan/common.c:45
 __kasan_record_aux_stack+0x95/0xb0  mm/kasan/generic.c:491
 kvfree_call_rcu+0x29/0xa80  kernel/rcu/tree.c:3328
 drop_sysctl_table+0x3be/0x4e0  fs/proc/proc_sysctl.c:1735
 unregister_sysctl_table.part.0+0x9c/0x190  fs/proc/proc_sysctl.c:1773
 unregister_sysctl_table+0x24/0x30  fs/proc/proc_sysctl.c:1753
 neigh_sysctl_unregister+0x5f/0x80  net/core/neighbour.c:3895
 addrconf_notify+0x140/0x17b0  net/ipv6/addrconf.c:3684
 notifier_call_chain+0xbe/0x210  kernel/notifier.c:87
 call_netdevice_notifiers_info+0xb5/0x150  net/core/dev.c:1937
 call_netdevice_notifiers_extack  net/core/dev.c:1975 [inline]
 call_netdevice_notifiers  net/core/dev.c:1989 [inline]
 dev_change_name+0x3c3/0x870  net/core/dev.c:1211
 dev_ifsioc+0x800/0xf70  net/core/dev_ioctl.c:376
 dev_ioctl+0x3d9/0xf80  net/core/dev_ioctl.c:542
 sock_do_ioctl+0x160/0x260  net/socket.c:1213
 sock_ioctl+0x3f9/0x670  net/socket.c:1316
 vfs_ioctl  fs/ioctl.c:51 [inline]
 __do_sys_ioctl  fs/ioctl.c:870 [inline]
 __se_sys_ioctl  fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x19e/0x210  fs/ioctl.c:856
 do_syscall_x64  arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3f/0x90  arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x72/0xdc

The buggy address belongs to the object at ffff888105b0e400
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 16 bytes inside of
 freed 1024-byte region [ffff888105b0e400, ffff888105b0e800)

The buggy address belongs to the physical page:
head:ffffea000416c200 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x200000000010200(slab|head|node=0|zone=2)
raw: 0200000000010200 ffff8881000430c0 ffffea00044c7010 ffffea0004510e10
raw: 0000000000000000 00000000000a000a 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888105b0e300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888105b0e380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888105b0e400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff888105b0e480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888105b0e500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

In summary, this patch solves those use-after-free by

1. Re-implement the nfc_llcp_find_local(). The current version does not
grab the reference when getting the local from the linked list.  For
example, the llcp_sock_bind() gets the reference like below:

// llcp_sock_bind()

    local = nfc_llcp_find_local(dev); // A
    ..... \
           | raceable
    ..... /
    llcp_sock->local = nfc_llcp_local_get(local); // B

There is an apparent race window that one can  drop the reference
and free the local object fetched in (A) before (B) gets the reference.

2. Some callers of the nfc_llcp_find_local() do not grab the reference
at all. For example, the nfc_genl_llc_{{get/set}_params/sdreq} functions.
We add the nfc_llcp_local_put() for them. Moreover, we add the necessary
error handling function to put the reference.

3. Add the nfc_llcp_remove_local() helper. The local object is removed
from the linked list in local_release() when all reference is gone. This
patch removes it when nfc_llcp_unregister_device() is called.

Therefore, every caller of nfc_llcp_find_local() will get a reference
even when the nfc_llcp_unregister_device() is called. This promises no
use-after-free for the local object is ever possible.

Fixes: 52feb444 ("NFC: Extend netlink interface for LTO, RW, and MIUX parameters support")
Fixes: c7aa1225 ("NFC: Take a reference on the LLCP local pointer when creating a socket")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>