linux-kernel - Re: [PATCH] nfc: llcp: avoid double release/put on LLCP_CLOSED in nfc_llcp_recv

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Message-ID: <579e05b2-4124-4883-ac97-f7ad294ba635@kernel.org>
Date: Wed, 17 Dec 2025 08:34:14 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Qianchang Zhao <pioooooooooip@...il.com>, Paolo Abeni
 <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Simon Horman <horms@...nel.org>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org, Zhitong Liu <liuzhitong1993@...il.com>
Subject: Re: [PATCH] nfc: llcp: avoid double release/put on LLCP_CLOSED in
 nfc_llcp_recv_disc()

On 17/12/2025 02:40, 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.

You did not answer to my questions, so I repeat the same question I
already asked you. Don't ignore reviewer's feedback.

> 
> 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.
> 
> Reported-by: Qianchang Zhao <pioooooooooip@...il.com>
> Reported-by: Zhitong Liu <liuzhitong1993@...il.com>

Drop both. You are the author, there are no reported-by credits for authors.

Missing Fixes tag.

> Cc: stable@...r.kernel.org
> Signed-off-by: Qianchang Zhao <pioooooooooip@...il.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);

So why now sending to closed socket is right?

> -	}
> -
>  	if (sk->sk_state == LLCP_CONNECTED) {
>  		nfc_put_device(local->dev);
>  		sk->sk_state = LLCP_CLOSED;

Best regards,
Krzysztof