[PATCH v1 net] nfc: llcp: Fix memleak in nfc_llcp_send_ui_frame().

[PATCH v1 net] nfc: llcp: Fix memleak in nfc_llcp_send_ui_frame().

[Kuniyuki Iwashima]

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/skbuff.c:6671
    sock_alloc_send_pskb+0x379/0x3e0 net/core/sock.c:2965
    sock_alloc_send_skb include/net/sock.h:1859 [inline]
    nfc_alloc_send_skb+0x45/0x80 net/nfc/core.c:724
    nfc_llcp_send_ui_frame+0x162/0x360 net/nfc/llcp_commands.c:766
    llcp_sock_sendmsg+0x14c/0x1d0 net/nfc/llcp_sock.c:814
    sock_sendmsg_nosec net/socket.c:727 [inline]
    __sock_sendmsg net/socket.c:742 [inline]
    __sys_sendto+0x2d8/0x2f0 net/socket.c:2244
    __do_sys_sendto net/socket.c:2251 [inline]
    __se_sys_sendto net/socket.c:2247 [inline]
    __x64_sys_sendto+0x28/0x30 net/socket.c:2247
    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

Fixes: 94f418a20664 ("NFC: UI frame sending routine implementation")
Reported-by: syzbot+f2d245f1d76bbfa50e4c@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/697569c7.a00a0220.33ccc7.0014.GAE@google.com/T/#u
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/nfc/llcp_commands.c | 17 ++++++++++++++++-
 net/nfc/llcp_core.c     |  4 +++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/net/nfc/llcp_commands.c b/net/nfc/llcp_commands.c
index e2680a3bef79..b652323bc2c1 100644
--- a/net/nfc/llcp_commands.c
+++ b/net/nfc/llcp_commands.c
@@ -778,8 +778,23 @@ int nfc_llcp_send_ui_frame(struct nfc_llcp_sock *sock, u8 ssap, u8 dsap,
 		if (likely(frag_len > 0))
 			skb_put_data(pdu, msg_ptr, frag_len);
 
+		spin_lock(&local->tx_queue.lock);
+
+		if (list_empty(&local->list)) {
+			spin_unlock(&local->tx_queue.lock);
+
+			kfree_skb(pdu);
+
+			len -= remaining_len;
+			if (len == 0)
+				len = -ENXIO;
+			break;
+		}
+
 		/* No need to check for the peer RW for UI frames */
-		skb_queue_tail(&local->tx_queue, pdu);
+		__skb_queue_tail(&local->tx_queue, pdu);
+
+		spin_unlock(&local->tx_queue.lock);
 
 		remaining_len -= frag_len;
 		msg_ptr += frag_len;
diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c
index beeb3b4d28ca..444a3774c8e8 100644
--- a/net/nfc/llcp_core.c
+++ b/net/nfc/llcp_core.c
@@ -316,7 +316,9 @@ static struct nfc_llcp_local *nfc_llcp_remove_local(struct nfc_dev *dev)
 	spin_lock(&llcp_devices_lock);
 	list_for_each_entry_safe(local, tmp, &llcp_devices, list)
 		if (local->dev == dev) {
-			list_del(&local->list);
+			spin_lock(&local->tx_queue.lock);
+			list_del_init(&local->list);
+			spin_unlock(&local->tx_queue.lock);
 			spin_unlock(&llcp_devices_lock);
 			return local;
 		}
-- 
2.52.0.457.g6b5491de43-goog

Re: [PATCH v1 net] nfc: llcp: Fix memleak in nfc_llcp_send_ui_frame().

[Simon Horman]

On Sun, Jan 25, 2026 at 12:59:28AM +0000, Kuniyuki Iwashima wrote:
> 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().

...

> Fixes: 94f418a20664 ("NFC: UI frame sending routine implementation")
> Reported-by: syzbot+f2d245f1d76bbfa50e4c@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/697569c7.a00a0220.33ccc7.0014.GAE@google.com/T/#u
> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>

Reviewed-by: Simon Horman <horms@kernel.org>

Re: [PATCH v1 net] nfc: llcp: Fix memleak in nfc_llcp_send_ui_frame().

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Sun, 25 Jan 2026 00:59:28 +0000 you wrote:
> 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().
> 
> [...]

Here is the summary with links:
  - [v1,net] nfc: llcp: Fix memleak in nfc_llcp_send_ui_frame().
    https://git.kernel.org/netdev/net/c/165c34fb6068

You are awesome, thank you!
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