CVE-2026-23150: nfc: llcp: Fix memleak in nfc_llcp_send_ui_frame().
In the Linux kernel, the following vulnerability has been resolved:

nfc: llcp: Fix memleak in nfc_llcp_send_ui_frame().

syzbot reported various memory leaks related to NFC, struct
nfc_llcp_sock, sk_buff, nfc_dev, etc. [0]

The leading log hinted that nfc_llcp_send_ui_frame() failed
to allocate skb due to sock_error(sk) being -ENXIO.

ENXIO is set by nfc_llcp_socket_release() when struct
nfc_llcp_local is destroyed by local_cleanup().

The problem is that there is no synchronisation between
nfc_llcp_send_ui_frame() and local_cleanup(), and skb
could be put into local->tx_queue after it was purged in
local_cleanup():

  CPU1                          CPU2
  ----                          ----
  nfc_llcp_send_ui_frame()      local_cleanup()
  |- do {                       '
     |- pdu = nfc_alloc_send_skb(..., &err)
     |                          .
     |                          |- nfc_llcp_socket_release(local, false, ENXIO);
     |                          |- skb_queue_purge(&local->tx_queue);      |
     |                          '                                          |
     |- skb_queue_tail(&local->tx_queue, pdu);                             |
    ...                                                                    |
     |- pdu = nfc_alloc_send_skb(..., &err)                                |
                                       ^._________________________________.'

local_cleanup() is called for struct nfc_llcp_local only
after nfc_llcp_remove_local() unlinks it from llcp_devices.

If we hold local->tx_queue.lock then, we can synchronise
the thread and nfc_llcp_send_ui_frame().

Let's do that and check list_empty(&local->list) before
queuing skb to local->tx_queue in nfc_llcp_send_ui_frame().

[0]:
[   56.074943][ T6096] llcp: nfc_llcp_send_ui_frame: Could not allocate PDU (error=-6)
[   64.318868][ T5813] kmemleak: 6 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
BUG: memory leak
unreferenced object 0xffff8881272f6800 (size 1024):
  comm "syz.0.17", pid 6096, jiffies 4294942766
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    27 00 03 40 00 00 00 00 00 00 00 00 00 00 00 00  '..@............
  backtrace (crc da58d84d):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4979 [inline]
    slab_alloc_node mm/slub.c:5284 [inline]
    __do_kmalloc_node mm/slub.c:5645 [inline]
    __kmalloc_noprof+0x3e3/0x6b0 mm/slub.c:5658
    kmalloc_noprof include/linux/slab.h:961 [inline]
    sk_prot_alloc+0x11a/0x1b0 net/core/sock.c:2239
    sk_alloc+0x36/0x360 net/core/sock.c:2295
    nfc_llcp_sock_alloc+0x37/0x130 net/nfc/llcp_sock.c:979
    llcp_sock_create+0x71/0xd0 net/nfc/llcp_sock.c:1044
    nfc_sock_create+0xc9/0xf0 net/nfc/af_nfc.c:31
    __sock_create+0x1a9/0x340 net/socket.c:1605
    sock_create net/socket.c:1663 [inline]
    __sys_socket_create net/socket.c:1700 [inline]
    __sys_socket+0xb9/0x1a0 net/socket.c:1747
    __do_sys_socket net/socket.c:1761 [inline]
    __se_sys_socket net/socket.c:1759 [inline]
    __x64_sys_socket+0x1b/0x30 net/socket.c:1759
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xfa0 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff88810fbd9800 (size 240):
  comm "syz.0.17", pid 6096, jiffies 4294942850
  hex dump (first 32 bytes):
    68 f0 ff 08 81 88 ff ff 68 f0 ff 08 81 88 ff ff  h.......h.......
    00 00 00 00 00 00 00 00 00 68 2f 27 81 88 ff ff  .........h/'....
  backtrace (crc 6cc652b1):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4979 [inline]
    slab_alloc_node mm/slub.c:5284 [inline]
    kmem_cache_alloc_node_noprof+0x36f/0x5e0 mm/slub.c:5336
    __alloc_skb+0x203/0x240 net/core/skbuff.c:660
    alloc_skb include/linux/skbuff.h:1383 [inline]
    alloc_skb_with_frags+0x69/0x3f0 net/core/sk
---truncated---
CVSS v3.1: 5.5