net: nfc: Fix use-after-free in local_cleanup()

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

net: nfc: Fix use-after-free in local_cleanup()

Fix a use-after-free that occurs in kfree_skb() called from
local_cleanup(). This could happen when killing nfc daemon (e.g. neard)
after detaching an nfc device.
When detaching an nfc device, local_cleanup() called from
nfc_llcp_unregister_device() frees local->rx_pending and decreases
local->ref by kref_put() in nfc_llcp_local_put().
In the terminating process, nfc daemon releases all sockets and it leads
to decreasing local->ref. After the last release of local->ref,
local_cleanup() called from local_release() frees local->rx_pending
again, which leads to the bug.

Setting local->rx_pending to NULL in local_cleanup() could prevent
use-after-free when local_cleanup() is called twice.

Found by a modified version of syzkaller.

BUG: KASAN: use-after-free in kfree_skb()

Call Trace:
dump_stack_lvl (lib/dump_stack.c:106)
print_address_description.constprop.0.cold (mm/kasan/report.c:306)
kasan_check_range (mm/kasan/generic.c:189)
kfree_skb (net/core/skbuff.c:955)
local_cleanup (net/nfc/llcp_core.c:159)
nfc_llcp_local_put.part.0 (net/nfc/llcp_core.c:172)
nfc_llcp_local_put (net/nfc/llcp_core.c:181)
llcp_sock_destruct (net/nfc/llcp_sock.c:959)
__sk_destruct (net/core/sock.c:2133)
sk_destruct (net/core/sock.c:2181)
__sk_free (net/core/sock.c:2192)
sk_free (net/core/sock.c:2203)
llcp_sock_release (net/nfc/llcp_sock.c:646)
__sock_release (net/socket.c:650)
sock_close (net/socket.c:1365)
__fput (fs/file_table.c:306)
task_work_run (kernel/task_work.c:179)
ptrace_notify (kernel/signal.c:2354)
syscall_exit_to_user_mode_prepare (kernel/entry/common.c:278)
syscall_exit_to_user_mode (kernel/entry/common.c:296)
do_syscall_64 (arch/x86/entry/common.c:86)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:106)

Allocated by task 4719:
kasan_save_stack (mm/kasan/common.c:45)
__kasan_slab_alloc (mm/kasan/common.c:325)
slab_post_alloc_hook (mm/slab.h:766)
kmem_cache_alloc_node (mm/slub.c:3497)
__alloc_skb (net/core/skbuff.c:552)
pn533_recv_response (drivers/nfc/pn533/usb.c:65)
__usb_hcd_giveback_urb (drivers/usb/core/hcd.c:1671)
usb_giveback_urb_bh (drivers/usb/core/hcd.c:1704)
tasklet_action_common.isra.0 (kernel/softirq.c:797)
__do_softirq (kernel/softirq.c:571)

Freed by task 1901:
kasan_save_stack (mm/kasan/common.c:45)
kasan_set_track (mm/kasan/common.c:52)
kasan_save_free_info (mm/kasan/genericdd.c:518)
__kasan_slab_free (mm/kasan/common.c:236)
kmem_cache_free (mm/slub.c:3809)
kfree_skbmem (net/core/skbuff.c:874)
kfree_skb (net/core/skbuff.c:931)
local_cleanup (net/nfc/llcp_core.c:159)
nfc_llcp_unregister_device (net/nfc/llcp_core.c:1617)
nfc_unregister_device (net/nfc/core.c:1179)
pn53x_unregister_nfc (drivers/nfc/pn533/pn533.c:2846)
pn533_usb_disconnect (drivers/nfc/pn533/usb.c:579)
usb_unbind_interface (drivers/usb/core/driver.c:458)
device_release_driver_internal (drivers/base/dd.c:1279)
bus_remove_device (drivers/base/bus.c:529)
device_del (drivers/base/core.c:3665)
usb_disable_device (drivers/usb/core/message.c:1420)
usb_disconnect (drivers/usb/core.c:2261)
hub_event (drivers/usb/core/hub.c:5833)
process_one_work (arch/x86/include/asm/jump_label.h:27 include/linux/jump_label.h:212 include/trace/events/workqueue.h:108 kernel/workqueue.c:2281)
worker_thread (include/linux/list.h:282 kernel/workqueue.c:2423)
kthread (kernel/kthread.c:319)
ret_from_fork (arch/x86/entry/entry_64.S:301)