Hi Krzysztof,
Sorry about that — my previous response might not have made it to the list/thread. Replying here to address your concerns before sending v3.
1) DM_DISC reply after LLCP_CLOSED This is not a new behavior introduced by my change. In the old code, the LLCP_CLOSED branch did release_sock() and nfc_llcp_sock_put(), but it did not return/goto, so execution continued and still reached nfc_llcp_send_dm(..., LLCP_DM_DISC) afterwards. The disc patch only removes the redundant CLOSED-branch cleanup so release_sock()/nfc_llcp_sock_put() are performed exactly once via the common exit path, while keeping the existing DM_DISC reply behavior.
2) Initial refcount / double free concern nfc_llcp_recv_disc()/recv_hdlc() take an extra reference via nfc_llcp_sock_get() (sock_hold()). The issue is the mismatched put/unlock: the CLOSED branch drops the reference and releases the lock, and then the common exit path does the same again. This is a refcount/locking imbalance regardless of whether it immediately frees the object, and it may become a UAF depending on timing/refcounting.
Regarding your formatting notes: I will wrap commit messages per submitting-patches, use a 12-char sha in Fixes, and run scripts/checkpatch.pl (and --strict) and fix reported warnings before sending v3.
Best regards, Qianchang
On Wed, Dec 17, 2025 at 9:57 PM Krzysztof Kozlowski krzk@kernel.org wrote:
On 17/12/2025 13:46, Qianchang Zhao wrote:
nfc_llcp_sock_get() takes a reference on the LLCP socket via sock_hold().
In nfc_llcp_recv_disc(), when the socket is already in LLCP_CLOSED state, the code used to perform release_sock() and nfc_llcp_sock_put() in the CLOSED branch but then continued execution and later performed the same cleanup again on the common exit path. This results in refcount imbalance (double put) and unbalanced
Please wrap commit message according to Linux coding style / submission process (neither too early nor over the limit): https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/process/submi...
lock release.
Remove the redundant CLOSED-branch cleanup so that release_sock() and nfc_llcp_sock_put() are performed exactly once via the common exit path, while keeping the existing DM_DISC reply behavior.
Fixes: d646960f7986fefb460a2b062d5ccc8ccfeacc3a ("NFC: Initial LLCP support")
12 char sha.
Please run scripts/checkpatch.pl on the patches and fix reported warnings. After that, run also 'scripts/checkpatch.pl --strict' on the patches and (probably) fix more warnings. Some warnings can be ignored, especially from --strict run, but the code here looks like it needs a fix. Feel free to get in touch if the warning is not clear.
Cc: stable@vger.kernel.org Signed-off-by: Qianchang Zhao pioooooooooip@gmail.com
net/nfc/llcp_core.c | 5 ----- 1 file changed, 5 deletions(-)
diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c index beeb3b4d2..ed37604ed 100644 --- a/net/nfc/llcp_core.c +++ b/net/nfc/llcp_core.c @@ -1177,11 +1177,6 @@ static void nfc_llcp_recv_disc(struct nfc_llcp_local *local,
nfc_llcp_socket_purge(llcp_sock);
if (sk->sk_state == LLCP_CLOSED) {release_sock(sk);nfc_llcp_sock_put(llcp_sock);You did not answer my previous review. You also did not answer my concerns from earlier private report. Please respond before you send again v3.
}if (sk->sk_state == LLCP_CONNECTED) { nfc_put_device(local->dev); sk->sk_state = LLCP_CLOSED;Best regards, Krzysztof