From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 221C62F7F02; Mon, 17 Aug 2026 14:41:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786977700; cv=none; b=fdO16IKNB5FkdGa9T37kDDofZw8zZqj5UabvgxpMLwl0x4tA9Z7ulcS+zx8j5VqZNxbtPq3EWTb8r7iXB/73+6hYJxq4iCS+5Fvz71HjBULeJi0DKH8k6mJj8FIDzr+eHzFv/r0ttJ1pXUqB2kMFh95W8p3+SVZ1XqDeODEEcjQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786977700; c=relaxed/simple; bh=kE4GpBymgBDQSLO5huYZQ8V+TfhGybyAb5n3/qJ8A+A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SLQi5dI0bmqsBxVsZkxNUK2KiKTpMUWI77eR5LYOk+aMZ+Jczas+NN4cSYnI45IABpZlWyrzi3xlYLl6p1KThNPb2bslNl44JMoWc7Y1wFPJa+/L7r4mVg0rEB34Pc8SrGQWm/B9t2COqqoSSxZoid4+i9h/jXBzebMvcdenyRQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=He2OAeSb; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="He2OAeSb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6E6A31F000E9; Mon, 17 Aug 2026 14:41:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786977699; bh=PGCzDT1Y+y961Al63zT6fPKX6U0vLW6KKtdTQaJVibo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=He2OAeSbbQCqzk1PMIlPAD7L4gWrBhzV9pdpdvz39xMnIbDQ0piTGxlblZfJEZkIb bZ8iv4B0qSR91JRp73qBHo0MEfGj9Ds2v7QlIzge/rlcRkoQ6Qhp4zRGtgooIaWW+x HTeLamz9JravpbA86KZnGyqXr8yqxbH8pu/p6joQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Siwei Zhang , Luiz Augusto von Dentz , Marco Elver , Sasha Levin , Todd Kjos Subject: [PATCH 5.15 419/456] Bluetooth: L2CAP: Fix UAF in channel timeout by holding conn ref Date: Mon, 17 Aug 2026 15:33:29 +0200 Message-ID: <20260817132555.597851940@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260817132539.792407575@linuxfoundation.org> References: <20260817132539.792407575@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Marco Elver [ Upstream commit b66774b48dd98f07254951f74ea6f513efe7ff8b ] l2cap_chan_timeout() runs asynchronously and accesses chan->conn. If the connection is torn down while the timer is running or pending, chan->conn can be freed, leading to a use-after-free when the timer worker attempts to lock conn->lock: | BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline] | BUG: KASAN: slab-use-after-free in atomic_long_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:4456 [inline] | BUG: KASAN: slab-use-after-free in __mutex_trylock_fast kernel/locking/mutex.c:161 [inline] | BUG: KASAN: slab-use-after-free in mutex_lock+0x4f/0xa0 kernel/locking/mutex.c:318 | Write of size 8 at addr ffff8881298d9550 by task kworker/2:1/83 | | CPU: 2 UID: 0 PID: 83 Comm: kworker/2:1 Not tainted 7.1.0-rc6-next-20260601-dirty #6 PREEMPT(full) | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014 | Workqueue: events l2cap_chan_timeout | Call Trace: | | instrument_atomic_read_write include/linux/instrumented.h:112 [inline] | atomic_long_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:4456 [inline] | __mutex_trylock_fast kernel/locking/mutex.c:161 [inline] | mutex_lock+0x4f/0xa0 kernel/locking/mutex.c:318 | l2cap_chan_timeout+0x5d/0x1b0 net/bluetooth/l2cap_core.c:422 | process_one_work kernel/workqueue.c:3326 [inline] | process_scheduled_works+0x7c8/0xfb0 kernel/workqueue.c:3409 | worker_thread+0x8a9/0xcf0 kernel/workqueue.c:3490 | kthread+0x346/0x430 kernel/kthread.c:436 | ret_from_fork+0x1a3/0x470 arch/x86/kernel/process.c:158 | ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 | | | Allocated by task 320: | l2cap_conn_add+0xa7/0x820 net/bluetooth/l2cap_core.c:7075 | l2cap_connect_cfm+0xdb/0xd70 net/bluetooth/l2cap_core.c:7452 | hci_connect_cfm include/net/bluetooth/hci_core.h:2139 [inline] | hci_remote_features_evt+0x52f/0x9f0 net/bluetooth/hci_event.c:3760 | hci_event_func net/bluetooth/hci_event.c:7796 [inline] | hci_event_packet+0x561/0xa70 net/bluetooth/hci_event.c:7847 | hci_rx_work+0x370/0x890 net/bluetooth/hci_core.c:4040 | process_one_work kernel/workqueue.c:3326 [inline] | process_scheduled_works+0x7c8/0xfb0 kernel/workqueue.c:3409 | worker_thread+0x8a9/0xcf0 kernel/workqueue.c:3490 | kthread+0x346/0x430 kernel/kthread.c:436 | ret_from_fork+0x1a3/0x470 arch/x86/kernel/process.c:158 | ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 | | Freed by task 322: | hci_disconn_cfm include/net/bluetooth/hci_core.h:2154 [inline] | hci_conn_hash_flush+0x101/0x1f0 net/bluetooth/hci_conn.c:2736 | hci_dev_close_sync+0x889/0xde0 net/bluetooth/hci_sync.c:5405 | hci_dev_do_close net/bluetooth/hci_core.c:502 [inline] | hci_unregister_dev+0x1f7/0x370 net/bluetooth/hci_core.c:2679 | vhci_release+0x12a/0x180 drivers/bluetooth/hci_vhci.c:690 | __fput+0x369/0x890 fs/file_table.c:510 | task_work_run+0x160/0x1d0 kernel/task_work.c:233 | get_signal+0xf5b/0x1120 kernel/signal.c:2810 | arch_do_signal_or_restart+0x4d/0x600 arch/x86/kernel/signal.c:337 | __exit_to_user_mode_loop kernel/entry/common.c:64 [inline] | exit_to_user_mode_loop+0x85/0x510 kernel/entry/common.c:98 | do_syscall_64+0x263/0x3d0 arch/x86/entry/syscall_64.c:100 | entry_SYSCALL_64_after_hwframe+0x77/0x7f | | The buggy address belongs to the object at ffff8881298d9400 | which belongs to the cache kmalloc-512 of size 512 | The buggy address is located 336 bytes inside of | freed 512-byte region [ffff8881298d9400, ffff8881298d9600) Fix it by having chan->conn hold a reference to l2cap_conn (via l2cap_conn_get) when the channel is added to the connection, and releasing it in the channel destructor. This ensures the l2cap_conn remains alive as long as the channel exists. A new FLAG_DEL channel flag is introduced to indicate that the channel has been deleted from its connection. l2cap_chan_del() atomically sets this flag using test_and_set_bit() instead of setting chan->conn to NULL. All asynchronous workers (l2cap_chan_timeout, l2cap_ack_timeout, l2cap_monitor_timeout, l2cap_retrans_timeout) and l2cap_chan_send() check FLAG_DEL to determine whether the channel has been torn down, rather than testing chan->conn for NULL. Fixes: 8c8e620467a7 ("Bluetooth: L2CAP: use chan timer to close channels in cleanup_listen()") Cc: Cc: Siwei Zhang Cc: Luiz Augusto von Dentz Assisted-by: Gemini:gemini-3.1-pro-preview Reported-by: https://sashiko.dev/#/patchset/20260521021249.3258069-1-oss%40fourdim.xyz Change-Id: Ie9862976d25c3e6d386689cd198ebe5ab4cc5509 Signed-off-by: Marco Elver Signed-off-by: Luiz Augusto von Dentz Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman Signed-off-by: Todd Kjos --- include/net/bluetooth/l2cap.h | 1 + net/bluetooth/l2cap_core.c | 36 +++++++++++++++++++++-------------- 2 files changed, 23 insertions(+), 14 deletions(-) diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h index beb690a162ff2..57315b9dc059e 100644 --- a/include/net/bluetooth/l2cap.h +++ b/include/net/bluetooth/l2cap.h @@ -776,6 +776,7 @@ enum { FLAG_ECRED_CONN_REQ_SENT, FLAG_PENDING_SECURITY, FLAG_HOLD_HCI_CONN, + FLAG_DEL, }; /* Lock nesting levels for L2CAP channels. We need these because lockdep diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 913c0d04a481a..bf031426c912e 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -435,7 +435,7 @@ static void l2cap_chan_timeout(struct work_struct *work) BT_DBG("chan %p state %s", chan, state_to_string(chan->state)); - if (!conn) { + if (!conn || test_bit(FLAG_DEL, &chan->flags)) { l2cap_chan_put(chan); return; } @@ -446,6 +446,9 @@ static void l2cap_chan_timeout(struct work_struct *work) */ l2cap_chan_lock(chan); + if (test_bit(FLAG_DEL, &chan->flags)) + goto unlock; + if (chan->state == BT_CONNECTED || chan->state == BT_CONFIG) reason = ECONNREFUSED; else if (chan->state == BT_CONNECT && @@ -458,10 +461,11 @@ static void l2cap_chan_timeout(struct work_struct *work) chan->ops->close(chan); +unlock: l2cap_chan_unlock(chan); - l2cap_chan_put(chan); mutex_unlock(&conn->chan_lock); + l2cap_chan_put(chan); } struct l2cap_chan *l2cap_chan_create(void) @@ -511,6 +515,9 @@ static void l2cap_chan_destroy(struct kref *kref) list_del(&chan->global_l); write_unlock(&chan_list_lock); + if (chan->conn) + l2cap_conn_put(chan->conn); + kfree(chan); } @@ -593,7 +600,7 @@ void __l2cap_chan_add(struct l2cap_conn *conn, struct l2cap_chan *chan) conn->disc_reason = HCI_ERROR_REMOTE_USER_TERM; - chan->conn = conn; + chan->conn = l2cap_conn_get(conn); switch (chan->chan_type) { case L2CAP_CHAN_CONN_ORIENTED: @@ -648,31 +655,28 @@ void l2cap_chan_add(struct l2cap_conn *conn, struct l2cap_chan *chan) void l2cap_chan_del(struct l2cap_chan *chan, int err) { - struct l2cap_conn *conn = chan->conn; - __clear_chan_timer(chan); - BT_DBG("chan %p, conn %p, err %d, state %s", chan, conn, err, + BT_DBG("chan %p, err %d, state %s", chan, err, state_to_string(chan->state)); chan->ops->teardown(chan, err); - if (conn) { - struct amp_mgr *mgr = conn->hcon->amp_mgr; + if (chan->conn && !test_and_set_bit(FLAG_DEL, &chan->flags)) { + struct amp_mgr *mgr = chan->conn->hcon->amp_mgr; + /* Delete from channel list */ list_del(&chan->list); l2cap_chan_put(chan); - chan->conn = NULL; - /* Reference was only held for non-fixed channels or * fixed channels that explicitly requested it using the * FLAG_HOLD_HCI_CONN flag. */ if (chan->chan_type != L2CAP_CHAN_FIXED || test_bit(FLAG_HOLD_HCI_CONN, &chan->flags)) - hci_conn_drop(conn->hcon); + hci_conn_drop(chan->conn->hcon); if (mgr && mgr->bredr_chan == chan) mgr->bredr_chan = NULL; @@ -2044,7 +2048,7 @@ static void l2cap_monitor_timeout(struct work_struct *work) l2cap_chan_lock(chan); - if (!chan->conn) { + if (!chan->conn || test_bit(FLAG_DEL, &chan->flags)) { l2cap_chan_unlock(chan); l2cap_chan_put(chan); return; @@ -2065,7 +2069,7 @@ static void l2cap_retrans_timeout(struct work_struct *work) l2cap_chan_lock(chan); - if (!chan->conn) { + if (!chan->conn || test_bit(FLAG_DEL, &chan->flags)) { l2cap_chan_unlock(chan); l2cap_chan_put(chan); return; @@ -2690,7 +2694,7 @@ int l2cap_chan_send(struct l2cap_chan *chan, struct msghdr *msg, size_t len) int err; struct sk_buff_head seg_queue; - if (!chan->conn) + if (!chan->conn || test_bit(FLAG_DEL, &chan->flags)) return -ENOTCONN; /* Connectionless channel */ @@ -3291,12 +3295,16 @@ static void l2cap_ack_timeout(struct work_struct *work) l2cap_chan_lock(chan); + if (test_bit(FLAG_DEL, &chan->flags)) + goto unlock; + frames_to_ack = __seq_offset(chan, chan->buffer_seq, chan->last_acked_seq); if (frames_to_ack) l2cap_send_rr_or_rnr(chan, 0); +unlock: l2cap_chan_unlock(chan); l2cap_chan_put(chan); } -- 2.53.0