This series fixes a refcount/locking imbalance in NFC LLCP receive handlers when the socket is already in LLCP_CLOSED.
nfc_llcp_recv_disc() used to perform release_sock()/nfc_llcp_sock_put() in the CLOSED branch but did not exit, and then performed the same cleanup again on the common exit path. Drop the redundant CLOSED-branch cleanup so the common exit path runs it exactly once, while keeping the existing DM_DISC reply behavior.
nfc_llcp_recv_hdlc() performed the CLOSED cleanup but then continued processing and later cleaned up again on the common exit path. Return immediately after the CLOSED cleanup.
Changes in v2: - Drop Reported-by tags - Add missing Fixes tags
Build-tested with: make M=net/nfc (no NFC HW available for runtime testing).
Qianchang Zhao (2): nfc: llcp: avoid double release/put on LLCP_CLOSED in nfc_llcp_recv_disc() nfc: llcp: stop processing on LLCP_CLOSED in nfc_llcp_recv_hdlc()
net/nfc/llcp_core.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-)
On 17/12/2025 14:05, くさあさ wrote:
Hi Krzysztof,
Sorry about that — my previous response might not have made it to the list/thread. Replying here to address your concerns before sending v3.
- DM_DISC reply after LLCP_CLOSED
This is not a new behavior introduced by my change. In the old code, the LLCP_CLOSED branch did release_sock() and nfc_llcp_sock_put(), but it did not return/goto, so execution continued and still reached nfc_llcp_send_dm(..., LLCP_DM_DISC) afterwards. The disc patch only removes the redundant CLOSED-branch cleanup so release_sock()/nfc_llcp_sock_put() are performed exactly once via the common exit path, while keeping the existing DM_DISC reply behavior.
I understand that you did not change the flow. I did not claim you did. I ask why do you think your code is correct.
Do not top post and do not send new versions while the discussion is still going.
- Initial refcount / double free concern
nfc_llcp_recv_disc()/recv_hdlc() take an extra reference via nfc_llcp_sock_get() (sock_hold()). The issue is the mismatched put/unlock: the CLOSED branch drops the reference and releases the lock, and then the common exit path does the same again. This is a refcount/locking imbalance regardless of whether it immediately frees the object, and it may become a UAF depending on timing/refcounting.
You did not really address the problem. The refcnt has imbalance only if you assume initial refcnt was 0.
Best regards, Krzysztof
I ask why do you think your code is correct.
Because the current code can execute release_sock()/nfc_llcp_sock_put() twice for the single ref acquired by nfc_llcp_sock_get(), and it can keep operating on llcp_sock/sk after the first put/unlock. The fix ensures exactly one cleanup (recv_disc) or exits immediately after the CLOSED cleanup (recv_hdlc), while keeping the existing DM_DISC send behavior.
The refcnt has imbalance only if you assume initial refcnt was 0.
No. Let baseline refcnt be N before nfc_llcp_sock_get(); sock_hold() makes N+1. CLOSED path put -> N, common exit put -> N-1. So it drops one extra ref regardless of N (whether it immediately frees depends on N). git blame shows both cleanup sites trace back to d646960f7986.
I will not send a new revision until this discussion is resolved.
Best regards, Qianchang
On Thu, Dec 18, 2025 at 7:22 PM Krzysztof Kozlowski krzk@kernel.org wrote:
On 17/12/2025 14:05, くさあさ wrote:
Hi Krzysztof,
Sorry about that — my previous response might not have made it to the list/thread. Replying here to address your concerns before sending v3.
- DM_DISC reply after LLCP_CLOSED
This is not a new behavior introduced by my change. In the old code, the LLCP_CLOSED branch did release_sock() and nfc_llcp_sock_put(), but it did not return/goto, so execution continued and still reached nfc_llcp_send_dm(..., LLCP_DM_DISC) afterwards. The disc patch only removes the redundant CLOSED-branch cleanup so release_sock()/nfc_llcp_sock_put() are performed exactly once via the common exit path, while keeping the existing DM_DISC reply behavior.
I understand that you did not change the flow. I did not claim you did. I ask why do you think your code is correct.
Do not top post and do not send new versions while the discussion is still going.
- Initial refcount / double free concern
nfc_llcp_recv_disc()/recv_hdlc() take an extra reference via nfc_llcp_sock_get() (sock_hold()). The issue is the mismatched put/unlock: the CLOSED branch drops the reference and releases the lock, and then the common exit path does the same again. This is a refcount/locking imbalance regardless of whether it immediately frees the object, and it may become a UAF depending on timing/refcounting.
You did not really address the problem. The refcnt has imbalance only if you assume initial refcnt was 0.
Best regards, Krzysztof
nfc_llcp_sock_get() takes a reference on the LLCP socket via sock_hold().
In nfc_llcp_recv_hdlc(), the LLCP_CLOSED branch releases the socket lock and drops the reference, but the function continues to operate on llcp_sock/sk and later runs release_sock() and nfc_llcp_sock_put() again on the common exit path.
Return immediately after the CLOSED cleanup to avoid refcount/lock imbalance and to avoid using the socket after dropping the reference.
Fixes: d646960f7986fefb460a2b062d5ccc8ccfeacc3a ("NFC: Initial LLCP support") Cc: stable@vger.kernel.org Signed-off-by: Qianchang Zhao pioooooooooip@gmail.com --- net/nfc/llcp_core.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c index ed37604ed..f6c1d79f9 100644 --- a/net/nfc/llcp_core.c +++ b/net/nfc/llcp_core.c @@ -1089,6 +1089,7 @@ static void nfc_llcp_recv_hdlc(struct nfc_llcp_local *local, if (sk->sk_state == LLCP_CLOSED) { release_sock(sk); nfc_llcp_sock_put(llcp_sock); + return; }
/* Pass the payload upstream */
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: d646960f7986fefb460a2b062d5ccc8ccfeacc3a ("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); - } - if (sk->sk_state == LLCP_CONNECTED) { nfc_put_device(local->dev); sk->sk_state = LLCP_CLOSED;
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/submi...
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@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);
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
Hi Krzysztof,
Sorry about that — my previous response might not have made it to the list/thread. Replying here to address your concerns before sending v3.
1) DM_DISC reply after LLCP_CLOSED This is not a new behavior introduced by my change. In the old code, the LLCP_CLOSED branch did release_sock() and nfc_llcp_sock_put(), but it did not return/goto, so execution continued and still reached nfc_llcp_send_dm(..., LLCP_DM_DISC) afterwards. The disc patch only removes the redundant CLOSED-branch cleanup so release_sock()/nfc_llcp_sock_put() are performed exactly once via the common exit path, while keeping the existing DM_DISC reply behavior.
2) Initial refcount / double free concern nfc_llcp_recv_disc()/recv_hdlc() take an extra reference via nfc_llcp_sock_get() (sock_hold()). The issue is the mismatched put/unlock: the CLOSED branch drops the reference and releases the lock, and then the common exit path does the same again. This is a refcount/locking imbalance regardless of whether it immediately frees the object, and it may become a UAF depending on timing/refcounting.
Regarding your formatting notes: I will wrap commit messages per submitting-patches, use a 12-char sha in Fixes, and run scripts/checkpatch.pl (and --strict) and fix reported warnings before sending v3.
Best regards, Qianchang
On Wed, Dec 17, 2025 at 9:57 PM Krzysztof Kozlowski krzk@kernel.org wrote:
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/submi...
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@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);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
linux-stable-mirror@lists.linaro.org
-
Krzysztof Kozlowski -
Qianchang Zhao -
くさあさ