linux-kernel - Re: [PATCH v3 1/2] nfc: llcp: avoid double release/put on LLCP_CLOSED in nfc_llcp_recv

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Message-ID: <c7851c67-dd52-41d4-b191-807aa5e26d9d@redhat.com>
Date: Sun, 28 Dec 2025 10:02:06 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Qianchang Zhao <pioooooooooip@...il.com>, netdev@...r.kernel.org
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Simon Horman <horms@...nel.org>, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org, Zhitong Liu <liuzhitong1993@...il.com>
Subject: Re: [PATCH v3 1/2] nfc: llcp: avoid double release/put on LLCP_CLOSED
 in nfc_llcp_recv_disc()

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@...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);

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