Re: PROBLEM: kernel NULL pointer dereference when yanking ftdi usb-serial during BREAK

[Dongliang Mu]

On Thu, Jun 8, 2023 at 10:37 AM Nick Bowler <nbowler@xxxxxxxxxx> wrote:
>
> Hi,
>
> I just hit an oops when unplugging my usb serial adapter.  So naturally,
> I tried it again, and found if I use minicom to send BREAK and then
> quickly yank the cable, I can reliably cause this oops every single
> time.
>
> Originally I noticed the problem on 6.1.7, but tried again on 6.4-rc5
> and the exact same problem occurs.
>
> Let me know if you need any more info!
>
> Thanks,
>   Nick
>
> [   41.834144] ftdi_sio 1-1:1.0: FTDI USB Serial Device converter detected
> [   41.834178] usb 1-1: Detected FT232R
> [   41.834307] usb 1-1: FTDI USB Serial Device converter now attached to ttyUSB0
> [   49.238361] usb 1-1: USB disconnect, device number 6
> [   49.238592] ftdi_sio ttyUSB0: error from flowcontrol urb
> [   49.238734] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now
> disconnected from ttyUSB0
> [   49.238760] ftdi_sio 1-1:1.0: device disconnected

According to the log, if I understand correctly, this driver first
disconnects, and then ftdi_break_ctl (operations about sending BREAK)
executes.
Clearly, it could lead to an UAF since priv is freed in the ftdi_port_remove.

I am not sure why there is a NULL pointer dereference since I did not
observe any explicit usb_set_serial_port_data(port, NULL);

The root cause may be due to the race between ftdi_port_remove and
ftdi_break_ctl. The fix can be a flag indicating if the device is
still presented.

Please correct me if you find any problem.

Dongliang Mu

> [   49.274543] BUG: kernel NULL pointer dereference, address: 000000000000000c
> [   49.274550] #PF: supervisor read access in kernel mode
> [   49.274553] #PF: error_code(0x0000) - not-present page
> [   49.274555] PGD 0 P4D 0
> [   49.274560] Oops: 0000 [#1] PREEMPT SMP
> [   49.274564] CPU: 3 PID: 3247 Comm: minicom Not tainted 6.4.0-rc5 #20
> [   49.274568] Hardware name: LENOVO 20CMCTO1WW/20CMCTO1WW, BIOS
> N10ET42W (1.21 ) 02/26/2016
> [   49.274572] RIP: 0010:ftdi_break_ctl+0x14/0x7b [ftdi_sio]
> [   49.274584] Code: c0 e8 64 63 6a d3 ba 06 00 00 00 31 f6 48 89 df
> 5b e9 5c fd ff ff 55 85 f6 89 f5 53 48 8b 9f 58 02 00 00 48 8b 83 48
> 03 00 00 <44> 8b 40 0c 74 06 66 41 81 c8 00 40 48 8b 13 45 0f b7 c0 b9
> 40 00
> [   49.274588] RSP: 0018:ffffb016009b3e28 EFLAGS: 00010246
> [   49.274591] RAX: 0000000000000000 RBX: ffffa3f944575800 RCX: 0000000000000000
> [   49.274593] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffffa3f940d8c400
> [   49.274595] RBP: 0000000000000000 R08: ffffa3fa65d9b840 R09: 0000000000000001
> [   49.274597] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000000000fa
> [   49.274599] R13: ffffa3f940d8c400 R14: 0000000000000000 R15: 0000000000000000
> [   49.274602] FS:  00007f0ffcedc740(0000) GS:ffffa3fa65d80000(0000)
> knlGS:0000000000000000
> [   49.274605] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   49.274607] CR2: 000000000000000c CR3: 000000010c981004 CR4: 00000000003706e0
> [   49.274610] Call Trace:
> [   49.274613]  <TASK>
> [   49.274614]  ? __die_body+0x15/0x53
> [   49.274620]  ? page_fault_oops+0x2e8/0x31c
> [   49.274625]  ? psi_group_change+0x237/0x298
> [   49.274631]  ? get_sd_balance_interval+0xf/0x39
> [   49.274637]  ? newidle_balance+0x25f/0x2c6
> [   49.274641]  ? exc_page_fault+0x14b/0x4b8
> [   49.274647]  ? asm_exc_page_fault+0x22/0x30
> [   49.274653]  ? ftdi_break_ctl+0x14/0x7b [ftdi_sio]
> [   49.274661]  serial_break+0x1c/0x1f [usbserial]
> [   49.274672]  send_break+0x7f/0xa6
> [   49.274678]  tty_ioctl+0x46e/0x6b3
> [   49.274683]  ? vfs_write+0x15d/0x188
> [   49.274688]  vfs_ioctl+0x16/0x23
> [   49.274692]  __do_sys_ioctl+0x52/0x74
> [   49.274698]  do_syscall_64+0x7f/0x9f
> [   49.274702]  entry_SYSCALL_64_after_hwframe+0x46/0xb0
> [   49.274708] RIP: 0033:0x7f0ffcfdec7b
> [   49.274711] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24
> 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00
> 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28
> 00 00
> [   49.274713] RSP: 002b:00007ffc18ab3a00 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000010
> [   49.274717] RAX: ffffffffffffffda RBX: 00005562830d74bc RCX: 00007f0ffcfdec7b
> [   49.274719] RDX: 0000000000000000 RSI: 0000000000005409 RDI: 0000000000000003
> [   49.274721] RBP: 0000556284ef1d60 R08: 00007f0ffd076440 R09: 0000000000000064
> [   49.274723] R10: 00007f0ffcee7450 R11: 0000000000000246 R12: 00005562830e9130
> [   49.274726] R13: 00007ffc18ab3ad0 R14: 00005562830d6ee8 R15: 0000000000000004
> [   49.274728]  </TASK>
> [   49.274730] Modules linked in: ftdi_sio usbserial ccm nfs lockd
> grace bridge stp llc xt_state iptable_filter iptable_mangle
> xt_MASQUERADE xt_mark iptable_nat nf_nat nf_conntrack nf_defrag_ipv6
> nf_defrag_ipv4 ip_tables x_tables snd_hda_codec_hdmi squashfs loop
> nls_iso8859_1 nls_cp437 vfat fat ext4 crc16 mbcache jbd2 iwlmvm i915
> mac80211 snd_ctl_led libarc4 snd_hda_codec_realtek
> snd_hda_codec_generic i2c_algo_bit drm_buddy drm_display_helper
> uvcvideo iwlwifi drivetemp videobuf2_vmalloc drm_kms_helper
> snd_hda_intel coretemp videobuf2_memops uvc snd_intel_dspcfg
> videobuf2_v4l2 syscopyarea x86_pkg_temp_thermal sysfillrect
> snd_hda_codec thinkpad_acpi sysimgblt cec videodev nvram snd_hda_core
> cfg80211 kvm_intel ttm ledtrig_audio snd_pcm videobuf2_common
> platform_profile jc42 regmap_i2c kvm irqbypass mc rfkill hwmon thermal
> drm intel_gtt ac snd_timer agpgart battery snd video soundcore wmi
> evdev efivarfs rtsx_pci_sdmmc mmc_core sha512_ssse3 e1000e rtsx_pci
> ptp mfd_core pps_core ipv6 sunrpc
> [   49.274823] CR2: 000000000000000c
> [   49.274825] ---[ end trace 0000000000000000 ]---
> [   49.274827] RIP: 0010:ftdi_break_ctl+0x14/0x7b [ftdi_sio]
> [   49.274835] Code: c0 e8 64 63 6a d3 ba 06 00 00 00 31 f6 48 89 df
> 5b e9 5c fd ff ff 55 85 f6 89 f5 53 48 8b 9f 58 02 00 00 48 8b 83 48
> 03 00 00 <44> 8b 40 0c 74 06 66 41 81 c8 00 40 48 8b 13 45 0f b7 c0 b9
> 40 00
> [   49.274838] RSP: 0018:ffffb016009b3e28 EFLAGS: 00010246
> [   49.274841] RAX: 0000000000000000 RBX: ffffa3f944575800 RCX: 0000000000000000
> [   49.274843] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffffa3f940d8c400
> [   49.274845] RBP: 0000000000000000 R08: ffffa3fa65d9b840 R09: 0000000000000001
> [   49.274847] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000000000fa
> [   49.274849] R13: ffffa3f940d8c400 R14: 0000000000000000 R15: 0000000000000000
> [   49.274851] FS:  00007f0ffcedc740(0000) GS:ffffa3fa65d80000(0000)
> knlGS:0000000000000000
> [   49.274853] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   49.274855] CR2: 000000000000000c CR3: 000000010c981004 CR4: 00000000003706e0
> [   49.274858] note: minicom[3247] exited with irqs disabled