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Date:   Sun, 09 Jul 2023 13:57:06 +0000
To:     "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>,
        Pauli Virtanen <pav@iki.fi>
From:   =?utf-8?Q?Barnab=C3=A1s_P=C5=91cze?= <pobrn@protonmail.com>
Subject: kernel NULL pointer dereference in hci_send_sco()
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Hi


while using a bluetooth headset with pipewire, I have run into the issue
in the subject multiple times already.

=09BUG: kernel NULL pointer dereference, address: 00000000000006a8
=09#PF: supervisor read access in kernel mode
=09#PF: error_code(0x0000) - not-present page
=09PGD 0 P4D 0=20
=09Oops: 0000 [#1] PREEMPT SMP PTI
=09CPU: 6 PID: 3472 Comm: pipewire-media- Tainted: P           OE      6.4.=
2-3-MANJARO #1 b8b1fec9d2ca7e610dcda537ef3912d54df433f4
=09Hardware name: SchenkerTechnologiesGmbH XMG FUSION 15 (XFU15L19)/LAPQC71=
A, BIOS QCCFL357.0120.2020.0813.1334 08/13/2020
=09RIP: 0010:hci_send_sco+0x17/0xb0 [bluetooth]
=09Code: f7 eb cf 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f =
00 0f 1f 44 00 00 41 56 49 89 fe 41 55 41 54 55 53 48 89 f3 <4c> 8b af a8 0=
6 00 00 66 90 48 89 df be 03 00 00 00 45 0f b7 66 32
=09RSP: 0018:ffffbdb60454fd38 EFLAGS: 00010216
=09RAX: 0000000000000001 RBX: ffff964f52e2f200 RCX: 0000000000000000
=09RDX: 0000000000000001 RSI: ffff964f52e2f200 RDI: 0000000000000000
=09RBP: ffff96538383f800 R08: ffffbdb60454fbd0 R09: 0000000000000000
=09R10: ffff9652bf1a8c80 R11: 0000000000000000 R12: ffff964f512a7680
=09R13: ffffbdb60454fdf8 R14: 0000000000000000 R15: ffffbdb60454fde8
=09FS:  00007f139fdff6c0(0000) GS:ffff965ebdb80000(0000) knlGS:000000000000=
0000
=09CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
=09CR2: 00000000000006a8 CR3: 0000000113a0e004 CR4: 00000000003706e0
=09Call Trace:
=09<TASK>
=09? __die+0x23/0x70
=09? page_fault_oops+0x171/0x4e0
=09? exc_page_fault+0x7f/0x180
=09? asm_exc_page_fault+0x26/0x30
=09? hci_send_sco+0x17/0xb0 [bluetooth 5eeccc5bad4c2f4e85d0f6a24ae9715b4720=
2498]
=09sco_sock_sendmsg+0x235/0x2e0 [bluetooth 5eeccc5bad4c2f4e85d0f6a24ae9715b=
47202498]
=09sock_sendmsg+0x93/0xa0
=09? sockfd_lookup_light+0x12/0x70
=09__sys_sendto+0x120/0x170
=09__x64_sys_sendto+0x24/0x30
=09do_syscall_64+0x5d/0x90
=09? exc_page_fault+0x7f/0x180
=09entry_SYSCALL_64_after_hwframe+0x72/0xdc
=09RIP: 0033:0x7f13a4b22dfc
=09Code: 89 4c 24 1c e8 f5 69 f7 ff 44 8b 54 24 1c 8b 3c 24 45 31 c9 89 c5 =
48 8b 54 24 10 48 8b 74 24 08 45 31 c0 b8 2c 00 00 00 0f 05 <48> 3d 00 f0 f=
f ff 77 34 89 ef 48 89 04 24 e8 41 6a f7 ff 48 8b 04
=09RSP: 002b:00007f139fdfd690 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
=09RAX: ffffffffffffffda RBX: 000000000000003c RCX: 00007f13a4b22dfc
=09RDX: 000000000000003c RSI: 000061500029bb00 RDI: 0000000000000041
=09RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
=09R10: 0000000000004040 R11: 0000000000000246 R12: 000061500029bb00
=09R13: 0000617000012d80 R14: 00000fe273d83b20 R15: 000000000000003c
=09</TASK>
=09Modules linked in: uinput nvidia_uvm(POE) rfcomm snd_seq_dummy snd_hrtim=
er snd_seq snd_seq_device nvidia_drm(POE) nvidia_modeset(POE) nvidia(POE) h=
id_ite8291r3(OE) qc71_laptop(OE) ccm cmac algif_hash algif_skcipher af_alg =
bnep snd_sof_pci_intel_cnl snd_sof_intel_hda_common soundwire_intel soundwi=
re_cadence snd_sof_intel_hda_mlink snd_sof_intel_hda snd_sof_pci snd_sof_xt=
ensa_dsp snd_sof snd_sof_utils snd_soc_hdac_hda snd_hda_ext_core snd_soc_ac=
pi_intel_match snd_soc_acpi soundwire_generic_allocation soundwire_bus ucsi=
_ccg snd_soc_core typec_ucsi snd_compress typec ac97_bus roles snd_pcm_dmae=
ngine btusb uvcvideo videobuf2_vmalloc btrtl uvc videobuf2_memops btbcm vid=
eobuf2_v4l2 btintel videodev btmtk videobuf2_common mc bluetooth ecdh_gener=
ic intel_rapl_msr intel_rapl_common intel_tcc_cooling x86_pkg_temp_thermal =
intel_powerclamp coretemp snd_hda_codec_hdmi kvm_intel iwlmvm snd_hda_codec=
_realtek kvm snd_hda_codec_generic irqbypass joydev mac80211 crct10dif_pclm=
ul vfat crc32_pclmul mousedev snd_hda_intel
=09polyval_clmulni fat polyval_generic libarc4 snd_intel_dspcfg gf128mul sn=
d_intel_sdw_acpi ghash_clmulni_intel sha512_ssse3 snd_hda_codec aesni_intel=
 iwlwifi crypto_simd snd_hda_core cryptd iTCO_wdt 8250_dw asus_wmi snd_hwde=
p hid_multitouch rapl ledtrig_audio intel_pmc_bxt mei_pxp mei_hdcp ee1004 i=
TCO_vendor_support intel_cstate snd_pcm spi_nor sparse_keymap cfg80211 inte=
l_uncore platform_profile snd_timer intel_wmi_thunderbolt wmi_bmof mei_me i=
ntel_lpss_pci r8168(OE) mtd pcspkr snd thunderbolt mei intel_lpss i2c_i801 =
i2c_hid_acpi rfkill i2c_nvidia_gpu intel_pch_thermal soundcore i2c_smbus id=
ma64 i2c_hid acpi_pad acpi_tad mac_hid dm_multipath vboxnetflt(OE) vboxneta=
dp(OE) vboxdrv(OE) crypto_user acpi_call(OE) fuse loop dm_mod bpf_preload i=
p_tables x_tables ext4 crc32c_generic crc16 mbcache jbd2 uas usbhid usb_sto=
rage i915 serio_raw atkbd i2c_algo_bit drm_buddy libps2 intel_gtt vivaldi_f=
map nvme drm_display_helper mxm_wmi nvme_core crc32c_intel spi_intel_pci ce=
c xhci_pci spi_intel nvme_common ttm
=09xhci_pci_renesas i8042 serio video wmi
=09CR2: 00000000000006a8
=09---[ end trace 0000000000000000 ]---
=09RIP: 0010:hci_send_sco+0x17/0xb0 [bluetooth]
=09Code: f7 eb cf 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f =
00 0f 1f 44 00 00 41 56 49 89 fe 41 55 41 54 55 53 48 89 f3 <4c> 8b af a8 0=
6 00 00 66 90 48 89 df be 03 00 00 00 45 0f b7 66 32
=09RSP: 0018:ffffbdb60454fd38 EFLAGS: 00010216
=09RAX: 0000000000000001 RBX: ffff964f52e2f200 RCX: 0000000000000000
=09RDX: 0000000000000001 RSI: ffff964f52e2f200 RDI: 0000000000000000
=09RBP: ffff96538383f800 R08: ffffbdb60454fbd0 R09: 0000000000000000
=09R10: ffff9652bf1a8c80 R11: 0000000000000000 R12: ffff964f512a7680
=09R13: ffffbdb60454fdf8 R14: 0000000000000000 R15: ffffbdb60454fde8
=09FS:  00007f139fdff6c0(0000) GS:ffff965ebdb80000(0000) knlGS:000000000000=
0000
=09CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
=09CR2: 00000000000006a8 CR3: 0000000113a0e004 CR4: 00000000003706e0
=09note: pipewire-media-[3472] exited with irqs disabled

Here is the disassembly:

=090000000000009fd0 <hci_send_sco>:
=099fd0:       f3 0f 1e fa             endbr64
=099fd4:       e8 00 00 00 00          call   9fd9 <hci_send_sco+0x9>
=09=09=09=099fd5: R_X86_64_PLT32    __fentry__-0x4
=099fd9:       41 56                   push   r14
=099fdb:       49 89 fe                mov    r14,rdi
=099fde:       41 55                   push   r13
=099fe0:       41 54                   push   r12
=099fe2:       55                      push   rbp
=099fe3:       53                      push   rbx
=099fe4:       48 89 f3                mov    rbx,rsi
=099fe7:       4c 8b af a8 06 00 00    mov    r13,QWORD PTR [rdi+0x6a8]
=099fee:       66 90                   xchg   ax,ax
=099ff0:       48 89 df                mov    rdi,rbx
=099ff3:       be 03 00 00 00          mov    esi,0x3
=099ff8:       45 0f b7 66 32          movzx  r12d,WORD PTR [r14+0x32]
=099ffd:       8b 6b 70                mov    ebp,DWORD PTR [rbx+0x70]
=09a000:       e8 00 00 00 00          call   a005 <hci_send_sco+0x35>
=09=09=09=09a001: R_X86_64_PLT32    skb_push-0x4

The offending instruction appears to be the mov at 0x9fe7. Based on the sou=
rce code:

=09void hci_send_sco(struct hci_conn *conn, struct sk_buff *skb)
=09{
=09=09struct hci_dev *hdev =3D conn->hdev;
=09=09struct hci_sco_hdr hdr;

=09=09BT_DBG("%s len %d", hdev->name, skb->len);

=09=09hdr.handle =3D cpu_to_le16(conn->handle);
=09=09hdr.dlen   =3D skb->len;

=09=09skb_push(skb, HCI_SCO_HDR_SIZE);

The offending part appears to be `conn->hdev`. It looks like `conn` is NULL=
.

I have spent some time looking at the code and it looks like `__sco_sock_cl=
ose()` is the only
place where `conn->hconn` is set to NULL, but that also sets `sk_state` to =
`BT_DISCONN`, so I
don't quite see how `sco_sock_sendmsg()` can then go ahead and call `sco_se=
nd_frame()` because
of the the following check:

=09if (sk->sk_state =3D=3D BT_CONNECTED)
=09=09err =3D sco_send_frame(sk, skb);
=09else
=09=09err =3D -ENOTCONN;

It is entirely possible that I am missing some part of the logic, so I may =
be completely wrong.
In any case, thank you for your help in advance.


Regards,
Barnab=C3=A1s P=C5=91cze