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Thu, 28 May 2026 00:56:47 -0700 (PDT) Received: from localhost ([111.228.63.84]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-841d72f8c7esm4273633b3a.52.2026.05.28.00.56.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2026 00:56:46 -0700 (PDT) From: Zhang Cen To: Marcel Holtmann , Luiz Augusto von Dentz Cc: linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, zerocling0077@gmail.com, 2045gemini@gmail.com Subject: [PATCH v2] Bluetooth: RFCOMM: hold listener socket in rfcomm_connect_ind() Date: Thu, 28 May 2026 15:56:41 +0800 Message-Id: <20260528075641.3416308-1-rollkingzzc@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" rfcomm_get_sock_by_channel() scans rfcomm_sk_list under the list lock, but returns the selected listener after dropping that lock without taking a reference. rfcomm_connect_ind() then locks the listener, queues a child socket on it, and may notify it after unlocking it. The buggy scenario involves two paths, with each column showing the order within that path: rfcomm_connect_ind(): listener close: 1. Find parent in 1. close() enters rfcomm_get_sock_by_channel() rfcomm_sock_release(). 2. Drop rfcomm_sk_list.lock 2. rfcomm_sock_shutdown() without pinning parent. closes the listener. 3. Call lock_sock(parent) and 3. rfcomm_sock_kill() bt_accept_enqueue(parent, unlinks and puts parent. sk, true). 4. Read parent flags and may 4. parent can be freed. call sk_state_change(). If close wins the race, parent can be freed before rfcomm_connect_ind() reaches lock_sock(), bt_accept_enqueue(), or the deferred-setup callback. Take a reference on the listener before leaving rfcomm_sk_list.lock. After lock_sock() succeeds, recheck that it is still in BT_LISTEN before queueing a child, cache the deferred-setup bit while the parent is locked, and drop the reference after the last parent use. KASAN reported a slab-use-after-free in lock_sock_nested() from rfcomm_connect_ind(), with the freeing stack going through rfcomm_sock_kill() and rfcomm_sock_release(). Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Zhang Cen --- v2: - Wrap the interleaving description to satisfy GitLint. - Add a Fixes tag. net/bluetooth/rfcomm/sock.c | 26 ++++++++++++++++++++++---- 1 file changed, 22 insertions(+), 4 deletions(-) diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c index 38d2355114cff..ed31d5f4fc76f 100644 --- a/net/bluetooth/rfcomm/sock.c +++ b/net/bluetooth/rfcomm/sock.c @@ -123,7 +123,7 @@ static struct sock *__rfcomm_get_listen_sock_by_addr(u8= channel, bdaddr_t *src) } =20 /* Find socket with channel and source bdaddr. - * Returns closest match. + * Returns closest match with an extra reference held. */ static struct sock *rfcomm_get_sock_by_channel(int state, u8 channel, bdad= dr_t *src) { @@ -137,15 +137,25 @@ static struct sock *rfcomm_get_sock_by_channel(int st= ate, u8 channel, bdaddr_t * =20 if (rfcomm_pi(sk)->channel =3D=3D channel) { /* Exact match. */ - if (!bacmp(&rfcomm_pi(sk)->src, src)) + if (!bacmp(&rfcomm_pi(sk)->src, src)) { + sock_hold(sk); break; + } =20 /* Closest match */ - if (!bacmp(&rfcomm_pi(sk)->src, BDADDR_ANY)) + if (!bacmp(&rfcomm_pi(sk)->src, BDADDR_ANY)) { + if (sk1) + sock_put(sk1); + sk1 =3D sk; + sock_hold(sk1); + } } } =20 + if (sk && sk1) + sock_put(sk1); + read_unlock(&rfcomm_sk_list.lock); =20 return sk ? sk : sk1; @@ -945,6 +955,7 @@ int rfcomm_connect_ind(struct rfcomm_session *s, u8 cha= nnel, struct rfcomm_dlc * { struct sock *sk, *parent; bdaddr_t src, dst; + bool defer_setup =3D false; int result =3D 0; =20 BT_DBG("session %p channel %d", s, channel); @@ -958,6 +969,11 @@ int rfcomm_connect_ind(struct rfcomm_session *s, u8 ch= annel, struct rfcomm_dlc * =20 lock_sock(parent); =20 + if (parent->sk_state !=3D BT_LISTEN) + goto done; + + defer_setup =3D test_bit(BT_SK_DEFER_SETUP, &bt_sk(parent)->flags); + /* Check for backlog size */ if (sk_acceptq_is_full(parent)) { BT_DBG("backlog full %d", parent->sk_ack_backlog); @@ -985,9 +1001,11 @@ int rfcomm_connect_ind(struct rfcomm_session *s, u8 c= hannel, struct rfcomm_dlc * done: release_sock(parent); =20 - if (test_bit(BT_SK_DEFER_SETUP, &bt_sk(parent)->flags)) + if (defer_setup) parent->sk_state_change(parent); =20 + sock_put(parent); + return result; } =20 --=20 2.43.0