Hi Sönke,
On Thu, Jul 21, 2022 at 3:16 AM Sönke Huster <soenke.huster@xxxxxxxxx> wrote:
>
> 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.
Yep that is most likely a Command Status being returned which isn't
expected for the commands above:
/* If command return a status event skb will be set to NULL as there are
* no parameters, in case of failure IS_ERR(skb) would have be set to
* the actual error would be found with PTR_ERR(skb).
*/
if (!skb)
return 0;
So perhaps we should convert these checks to IS_ERR_OR_NULL.
> Best
> Sönke
--
Luiz Augusto von Dentz
