Re: [BUG] Page Fault in hci_inquiry_result_with_rssi_evt

[Luiz Augusto von Dentz <luiz.dentz@gmail.com>]

Hi Sönke,

On Tue, Jan 4, 2022 at 3:50 AM Sönke Huster <soenke.huster@eknoes.de> wrote:
>
> Hi Luiz,
>
> On 04.01.22 01:38, Luiz Augusto von Dentz wrote:
> > Hi Sönke,
> >
> > On Mon, Jan 3, 2022 at 3:41 PM Sönke Huster <soenke.huster@eknoes.de> wrote:
> >>
> >> Hello,
> >>
> >> While fuzzing bluetooth-next I found the following bug:
> >>
> >> [   27.333034] BUG: unable to handle page fault for address: fffff61a1a1a1a1a
> >> [   27.333241] #PF: supervisor read access in kernel mode
> >> [   27.333241] #PF: error_code(0x0000) - not-present page
> >> [   27.333241] PGD 6dfd2067 P4D 6dfd2067 PUD 0
> >> [   27.333241] Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
> >> [   27.333241] CPU: 0 PID: 45 Comm: kworker/u3:2 Not tainted 5.16.0-rc1+ #81
> >> [   27.333241] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> >> [   27.333241] Workqueue: hci0 hci_rx_work
> >> [   27.333241] RIP: 0010:hci_inquiry_result_with_rssi_evt+0xbc/0x950
> >> [   27.333241] Code: 8b 04 24 48 c1 e8 03 42 80 3c 28 00 0f 85 20 07 00 00 48 8b 04 24 4c 8b 28 48 b8 00 00 00 00 00 fc ff df 4c 89 0
> >> [   27.333241] RSP: 0018:ffffc900004ff9c8 EFLAGS: 00010212
> >> [   27.333241] RAX: dffffc0000000000 RBX: 0000000000000022 RCX: ffffffff834663d1
> >> [   27.333241] RDX: 1ffffa1a1a1a1a1a RSI: 0000000000000012 RDI: ffff88800affb074
> >> [   27.333241] RBP: ffff88800aae0000 R08: ffffffff844ef360 R09: ffffffff83487b35
> >> [   27.333241] R10: 000000000000002c R11: 0000000000000022 R12: ffff88800affb000
> >> [   27.333241] R13: ffffd0d0d0d0d0d0 R14: 0000000000000000 R15: ffff88800aae0000
> >> [   27.333241] FS:  0000000000000000(0000) GS:ffff88806ce00000(0000) knlGS:0000000000000000
> >> [   27.333241] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> [   27.333241] CR2: fffff61a1a1a1a1a CR3: 0000000004a26000 CR4: 00000000000006f0
> >> [   27.333241] Call Trace:
> >> [   27.333241]  <TASK>
> >> [   27.333241]  ? wait_for_completion_io+0x270/0x270
> >> [   27.333241]  ? hci_inquiry_result_evt+0x4b0/0x4b0
> >> [   27.333241]  hci_event_packet+0x3b11/0x7b10
> >> [   27.333241]  ? lock_chain_count+0x20/0x20
> >> [   27.333241]  ? hci_cmd_status_evt.constprop.0+0x4ea0/0x4ea0
> >> [   27.333241]  ? sysvec_reboot+0x50/0xc0
> >> [   27.333241]  ? find_held_lock+0x2c/0x110
> >> [   27.333241]  ? lock_release+0x3b2/0x6f0
> >> [   27.333241]  ? skb_dequeue+0x110/0x1a0
> >> [   27.333241]  ? mark_held_locks+0x9e/0xe0
> >> [   27.333241]  ? lockdep_hardirqs_on_prepare+0x17b/0x400
> >> [   27.333241]  hci_rx_work+0x4d3/0xb90
> >> [   27.333241]  process_one_work+0x904/0x1590
> >> [   27.333241]  ? lock_release+0x6f0/0x6f0
> >> [   27.333241]  ? pwq_dec_nr_in_flight+0x230/0x230
> >> [   27.333241]  ? rwlock_bug.part.0+0x90/0x90
> >> [   27.333241]  ? _raw_spin_lock_irq+0x41/0x50
> >> [   27.333241]  worker_thread+0x578/0x1310
> >> [   27.333241]  ? process_one_work+0x1590/0x1590
> >> [   27.333241]  kthread+0x3b2/0x490
> >> [   27.333241]  ? _raw_spin_unlock_irq+0x1f/0x40
> >> [   27.333241]  ? set_kthread_struct+0x100/0x100
> >> [   27.333241]  ret_from_fork+0x22/0x30
> >> [   27.333241]  </TASK>
> >> [   27.333241] Modules linked in:
> >> [   27.333241] CR2: fffff61a1a1a1a1a
> >> [   27.333241] ---[ end trace 6a6825484c8fefa6 ]---
> >> [   27.333241] RIP: 0010:hci_inquiry_result_with_rssi_evt+0xbc/0x950
> >> [   27.333241] Code: 8b 04 24 48 c1 e8 03 42 80 3c 28 00 0f 85 20 07 00 00 48 8b 04 24 4c 8b 28 48 b8 00 00 00 00 00 fc ff df 4c 89 0
> >> [   27.333241] RSP: 0018:ffffc900004ff9c8 EFLAGS: 00010212
> >> [   27.333241] RAX: dffffc0000000000 RBX: 0000000000000022 RCX: ffffffff834663d1
> >> [   27.333241] RDX: 1ffffa1a1a1a1a1a RSI: 0000000000000012 RDI: ffff88800affb074
> >> [   27.333241] RBP: ffff88800aae0000 R08: ffffffff844ef360 R09: ffffffff83487b35
> >> [   27.333241] R10: 000000000000002c R11: 0000000000000022 R12: ffff88800affb000
> >> [   27.333241] R13: ffffd0d0d0d0d0d0 R14: 0000000000000000 R15: ffff88800aae0000
> >> [   27.333241] FS:  0000000000000000(0000) GS:ffff88806ce00000(0000) knlGS:0000000000000000
> >> [   27.333241] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> [   27.333241] CR2: fffff61a1a1a1a1a CR3: 0000000004a26000 CR4: 00000000000006f0
> >> [   27.379996] kworker/u3:2 (45) used greatest stack depth: 27736 bytes left
> >>
> >> It occurs when sending the following frame to the kernel:
> >>
> >> $ xxd crashes/hci_inquiry_result_with_rssi_evt
> >> 00000000: 0422 24d0 d0d0 d0d0 d0ff ff              ."$........
> >>
> >> The bug was introduced with the commit "Bluetooth: HCI: Use skb_pull_data to parse Inquiry Result with RSSI event" (https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git/commit/?id=8d08d324fdcb7).
> >
> > That is pretty weird, the data seems to be the following:
> >
> > 04 -> HCI_EVENT_PKT
> > 22 -> HCI_EV_INQUIRY_RESULT_WITH_RSSI
> > 24 -> hci_ev_inquiry_result_rssi.num
> > d0 d0d0 d0d0 d0ff ff
> >
> > But this should never evaluate to true for:
> >
> > if (skb->len == flex_array_size(ev, res2->info, ev->res2->num)) {
> > ...
> > } else if (skb->len == flex_array_size(ev, res1->info, ev->res1->num)) {
> >
>
> I'm sorry, I forgot to mention the affected source code, the check seems to be too late. GDB says it is already happening in net/bluetooth/hci_event.c:4519:
>
> (gdb) list *hci_inquiry_result_with_rssi_evt+0x9b
> 0xffffffff83470d8b is in hci_inquiry_result_with_rssi_evt (net/bluetooth/hci_event.c:4519).
> 4514            struct inquiry_data data;
> 4515            int i;
> 4516
> 4517            bt_dev_dbg(hdev, "num_rsp %d", ev->res1->num);
> 4518
> 4519            if (!ev->res1->num) # <- page fault here
> 4520                    return;
>
> I just reproduced it on the HEAD of bluetooth-next (for-net-next-2021-12-29).

That would mean there is less data than the hci_ev.min_len, but that
is checked in hci_event_func prior to calling the hci_ev.func:

if (skb->len < ev->min_len) {
bt_dev_err(hdev, "unexpected event 0x%2.2x length: %u < %u",
   event, skb->len, ev->min_len);
return;
}

>
> > These requires the data to be multiple of sizeof(struct
> > inquiry_info_rssi_pscan) = 15 bytes or sizeof(struct
> > inquiry_info_rssi) = 14 bytes respectively where the data left is just
> > 8 bytes long, besides with the number of entries being 0x24 this shall
> > be well beyond skb->len which shall have cause the else clause:
> >
> >   } else {
> >       bt_dev_err(hdev, "Malformed HCI Event: 0x%2.2x",
> >                          HCI_EV_INQUIRY_RESULT_WITH_RSSI);
> >   }
> >
>
> I think prior to the commit that introduced that, the check was made before casting it to the struct, so from the "raw" skb->data:
>
> -       int num_rsp = *((__u8 *) skb->data);
> -       if ((skb->len - 1) / num_rsp != sizeof(struct inquiry_info_with_rssi)) {

That is still being checked, anyway that would cause a page fault when
accessing num_rsp so I don't understand why it would cause a page
fault now when previously it didn't even check if there were any bytes
to be read, perhaps there is some memory alignment at play.

> > Anyway the bluetooth-next has been updated since last week so I first
> > attempt to reproduce with a fresh clone of it since we did some fixups
> > since then.
> >
>
> Btw, what is the best way to provide an easily reproducible bug report here, I did not figure that out yet.
>
> Also, when searching for bugs (to ideally provide patches), I am currently searching on the HEAD of bluetooth-next. As far as I understood it, the tags "for-net-..." should be more or less stable, as they are merged to net-next which makes its way to mainline, right?

Yep, those are the tags we sent to net-next but in general
bluetooth-next shall also be stable since we run CI on every patch
nowadays.

-- 
Luiz Augusto von Dentz