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

Paolo Abeni
2025-12-28T09:16:08Z

On 12/28/25 10:02 AM, Paolo Abeni wrote:
> 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);
> }

I'm sorry for the confusing feedback above.

I read the comments on patch 2/2 only after processing this one.

Indeed following the half-interrupted discussion on old revision, with
bad patch splitting is quite difficult.

@Qianchang Zhao: my _guess_ is that on LLCP_CLOSED the code has to
release the final sk reference... In any case discussion an a patch
series revision is not concluded until the reviewer agrees on that.

@Krzysztof: ... but still it looks like in the current code there is a
double release on the sk socket lock, which looks wrong, what am I
missing here?

/P