linux-kernel - Re: [PATCH v2 1/2] nfc: llcp: avoid double release/put on LLCP_CLOSED in nfc_llcp_recv

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Message-ID: <ebb7cb16-781b-4f33-b7c0-3c5dd383913c@kernel.org>
Date: Wed, 17 Dec 2025 13:57:27 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Qianchang Zhao <pioooooooooip@...il.com>, linux-nfc@...ts.01.org
Cc: Paolo Abeni <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>,
 "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
Subject: Re: [PATCH v2 1/2] nfc: llcp: avoid double release/put on LLCP_CLOSED
 in nfc_llcp_recv_disc()

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/submitting-patches.rst#L597

> 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@...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);

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