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Date:   Thu, 21 Jul 2022 12:16:05 +0200
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To:     Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Marcel Holtmann <marcel@holtmann.org>
Cc:     linux-bluetooth@vger.kernel.org
From:   =?UTF-8?Q?S=c3=b6nke_Huster?= <soenke.huster@eknoes.de>
Subject: [BUG] Null pointer deref in aosp_do_open/msft_do_open
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Precedence: bulk

Hi,

My fuzzer found two null pointer exceptions in aosp_do_open and msft_do_open, both triggered by the
same frame sequence on the current bluetooth-next master.

      BUG: kernel NULL pointer dereference, address: 0000000000000070
      #PF: supervisor read access in kernel mode
      #PF: error_code(0x0000) - not-present page
      PGD 0 P4D 0 
      Oops: 0000 [#1] PREEMPT SMP NOPTI
      CPU: 0 PID: 41 Comm: kworker/u3:0 Not tainted 5.18.0-rc7-00850-g33b44d809538 #1
      Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
      Workqueue: hci0 hci_power_on
      RIP: 0010:aosp_do_open+0x7e/0x230
      Call Trace:
       <TASK>
       hci_dev_open_sync+0x98b/0x1060
       hci_power_on+0x84/0x350
       process_one_work+0x2a6/0x5d0
       worker_thread+0x4a/0x3d0
       ? process_one_work+0x5d0/0x5d0
       kthread+0xed/0x120
       ? kthread_complete_and_exit+0x20/0x20
       ret_from_fork+0x22/0x30
       </TASK>

The null pointer deref occurs in the skb length check (net/bluetooth/aosp.c:64), the skb returned
previously by __hci_cmd_sync is null: 

	/* LE Get Vendor Capabilities Command */
	skb = __hci_cmd_sync(hdev, hci_opcode_pack(0x3f, 0x153), 0, NULL,
			     HCI_CMD_TIMEOUT);
	if (IS_ERR(skb)) {
		bt_dev_err(hdev, "AOSP get vendor capabilities (%ld)",
			   PTR_ERR(skb));
		return;
	}

	/* A basic length check */
	if (skb->len < VENDOR_CAPA_BASE_SIZE)
	
Bisected to: [d0b137062b2de75b264b84143d21c98abc5f5ad2] Bluetooth: hci_sync: Rework init stages

It occurs when an AOSP resp. MSFT capable controller sends the following two different
Command Status (0x0f) for Reset (0x0c03) on initialization:

Status Octet: Unknown HCI Command (0x01)
0000   04 0f 04 01 02 03 0c

Status Octet: Pending (0x00)
0000   04 0f 04 00 02 03 0c

The problem seems to be that __hci_cmd_sync returns null, and not an PTR_ERR. The affected code
for msft_do_open is similar (msft.c:128ff):

	skb = __hci_cmd_sync(hdev, hdev->msft_opcode, sizeof(cp), &cp,
			     HCI_CMD_TIMEOUT);
	if (IS_ERR(skb)) {
		bt_dev_err(hdev, "Failed to read MSFT supported features (%ld)",
			   PTR_ERR(skb));
		return false;
	}

	if (skb->len < sizeof(*rp)) {

Which one is triggered depends on the device reporting itself as either AOSP or MSFT capable.
If it indicates both, it depends on timing.

I think that can only be triggered by a malicious or broken Bluetooth controller, but there
might be an underlying issue with __hci_cmd_sync returning null instead of an ERR_PTR.

Best
Sönke