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Tue, 06 Oct 2026 07:39:28 -0700 (PDT) From: Cen Zhang To: marcel@holtmann.org, luiz.dentz@gmail.com Cc: linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, jjzuming@gmail.com, zzzccc427@gmail.com Subject: [PATCH] Bluetooth: hci_sync: Serialize devcoredump reset during device open Date: Tue, 6 Oct 2026 22:39:21 +0800 Message-Id: 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-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit An ACTIVE devcoredump's buffer cursors must remain valid from the packet handler's state check through its copy. hci_devcd_rx() holds hdev->lock across that interval, and hci_devcd_reset() requires the same lock. However, hci_dev_open_sync() invokes reset without taking it. A registered VHCI controller can collect a dump through its debugfs interface while the controller is down. If a successful open overlaps with handling a nonempty dump packet, reset can run after the receiver's ACTIVE check and before its copy: hci_devcd_rx() hci_dev_open_sync() dequeue nonempty skb hci_dev_lock(hdev) handler observes ACTIVE hdev->open(hdev) succeeds hci_devcd_reset(hdev) dump.tail = NULL dump.state = IDLE hci_devcd_copy() compare against old dump.end memcpy(NULL, ..., skb->len) hci_dev_unlock(hdev) Reset leaves dump.end pointing at the old buffer and purges only queued packets, so it cannot discard the skb already dequeued by the receiver. The bounds check can pass with a NULL tail, leading to a nonempty copy to address zero. KASAN reported a 24-byte NULL write in hci_devcd_rx(). Take hdev->lock around the open-time reset. The receiver then finishes its state check and copy using valid cursors before reset, or observes IDLE after reset and skips the copy. KASAN report as below: BUG: KASAN: null-ptr-deref in hci_devcd_rx+0x5d5/0x1a80 Write of size 24 at addr 0000000000000000 by task kworker/u17:0/496 CPU: 0 UID: 0 PID: 496 Comm: kworker/u17:0 Not tainted 7.2.0-rc6-pmb-bt-functional-v1+ #1 PREEMPT(lazy) Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: hci0 hci_devcd_rx Call Trace: dump_stack_lvl+0x93/0xd0 kasan_report+0xe0/0x110 ? hci_devcd_rx+0x5d5/0x1a80 kasan_check_range+0x105/0x1b0 __asan_memcpy+0x3c/0x60 hci_devcd_rx+0x5d5/0x1a80 ? srso_alias_return_thunk+0x5/0xfbef5 ? __pfx_hci_devcd_rx+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? lock_release+0xc8/0x280 ? srso_alias_return_thunk+0x5/0xfbef5 process_one_work+0x908/0x19c0 ? __pfx_process_one_work+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? lock_is_held_type+0x8f/0x100 ? srso_alias_return_thunk+0x5/0xfbef5 worker_thread+0x65c/0xe40 ? __pfx_worker_thread+0x10/0x10 kthread+0x34f/0x460 ? srso_alias_return_thunk+0x5/0xfbef5 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x659/0x940 ? __pfx_ret_from_fork+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? __switch_to+0x74f/0xf80 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 ================================================================== Disabling lock debugging due to kernel taint Fixes: 9695ef876fd1 ("Bluetooth: Add support for hci devcoredump") Assisted-by: LLM Signed-off-by: Cen Zhang --- diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c index 1fe11d3ef1aaa8118811fb778b591e0413b4b3f0..8e4fc26b3c42d72a33393bd0b381414c4c0f927e 100644 --- a/net/bluetooth/hci_sync.c +++ b/net/bluetooth/hci_sync.c @@ -5454,7 +5454,9 @@ int hci_dev_open_sync(struct hci_dev *hdev) goto done; } + hci_dev_lock(hdev); hci_devcd_reset(hdev); + hci_dev_unlock(hdev); set_bit(HCI_RUNNING, &hdev->flags); hci_sock_dev_event(hdev, HCI_DEV_OPEN);