Hi Luiz, On 04.01.22 22:04, Luiz Augusto von Dentz wrote: > Hi Sönke, > > On Tue, Jan 4, 2022 at 11:31 AM Luiz Augusto von Dentz > <luiz.dentz@xxxxxxxxx> wrote: >> >> Hi Sönke, >> >> On Tue, Jan 4, 2022 at 3:50 AM Sönke Huster <soenke.huster@xxxxxxxxx> 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@xxxxxxxxx> 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. > > Ive just sent a patch trying to eliminate the use of the union since > that perhaps cause the compiler to use a different alignment, Im also The patch fixes it, I can't reproduce it anymore and the kernel log shows the expected "Bluetooth: hci0: Malformed HCI Event: 0x22". > thinking on introducing some mechanism to our emulator to generate > arbitrary events in a form a command that generates an event based on > its parameter. > > https://patchwork.kernel.org/project/bluetooth/patch/20220104210051.2982871-1-luiz.dentz@xxxxxxxxx/ >
