Re: [PATCH v3 1/2] nfc: llcp: avoid double release/put on LLCP_CLOSED in nfc_llcp_recv_disc()

Paolo Abeni
2025-12-28T09:02:14Z

On 12/18/25 3:59 AM, 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 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: d646960f7986 ("NFC: Initial LLCP support")
> 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);

To rephrase Krzysztof concernt, this does not looks like the correct
fix: later on nfc_llcp_recv_disc() will try a send over a closed socket,
which looks wrong. Instead you could just return after
nfc_llcp_sock_put(), or do something alike:

if (sk->sk_state == LLCP_CLOSED)
goto cleanup;

// ...

cleanup:
release_sock(sk);
nfc_llcp_sock_put(llcp_sock);
}

/P