Re: linux 5.14.3: free_user_ns causes NULL pointer dereference

[Alexey Gladkov]

On Thu, Sep 16, 2021 at 12:30:44PM -0500, Eric W. Biederman wrote:
> Jordan Glover <Golden_Miller83@xxxxxxxxxxxxx> writes:
> 
> > On Wednesday, September 15th, 2021 at 10:42 PM, Jordan Glover <Golden_Miller83@xxxxxxxxxxxxx> wrote:
> >>
> >> I had about 2 containerized (flatpak/bubblewrap) apps (browser + music player) running . I quickly closed them with intent to shutdown the system but instead get the freeze and had to use magic sysrq to reboot. System logs end with what I posted and before there is nothing suspicious.
> >>
> >> Maybe it's some random fluke. I'll reply if I hit it again.
> >
> > Heh, it jut happened again. This time closing firefox alone had such
> > effect:
> 
> Ok. It looks like he have a couple of folks seeing issues here.
> 
> I thought we had all of the issues sorted out for the release of v5.14,
> but it looks like there is still some little bug left.
> 
> If Alex doesn't beat me to it I will see if I can come up with a
> debugging patch to make it easy to help track down where the reference
> count is going wrong.   It will be a little bit as my brain is mush at
> the moment.

I'm poking it right now, but so far without much success.

The dec_ucount() happened free_user_ns(). There we only decrease the
UCOUNT_USER_NAMESPACES in the user_ns tree. Perhaps somewhere someone
forgot to do create_user_ns() ?

> Eric
> 
> > ------------[ cut here ]------------
> > WARNING: CPU: 1 PID: 351 at kernel/ucount.c:253 dec_ucount+0x43/0x50
> > Modules linked in: nft_ct nft_fib_ipv4 nft_fib wireguard curve25519_x86_64 libcurve25519_generic libchacha20poly1305 chacha_x86_64 poly1305_x86_64 udp_tunnel libblake2s blake2s_x86_64 libblake2s_generic libchacha ccm algif_aead des_generic libdes ecb algif_skcipher cmac md4 algif_hash af_alg hid_sensor_custom_intel_hinge hid_sensor_als hid_sensor_gyro_3d hid_sensor_accel_3d hid_sensor_rotation hid_sensor_magn_3d hid_sensor_trigger industrialio_triggered_buffer hid_sensor_iio_common kfifo_buf industrialio hid_sensor_custom hid_sensor_hub cros_ec_ishtp cros_ec intel_ishtp_loader intel_ishtp_hid intel_rapl_msr nft_counter xt_mark ipt_REJECT nf_reject_ipv4 mei_hdcp intel_rapl_common xt_LOG nf_log_syslog intel_tcc_cooling x86_pkg_temp_thermal think_lmi wmi_bmof xt_addrtype firmware_attributes_class xt_tcpudp intel_powerclamp xt_conntrack nf_conntrack nf_defrag_ipv4 snd_hda_codec_hdmi nft_compat intel_wmi_thunderbolt nf_tables libcrc32c coretemp iwlmvm snd_ctl_led nfnetlink
> >  snd_hda_codec_conexant mac80211 snd_hda_codec_generic libarc4 vfat snd_hda_intel kvm_intel fat iwlwifi snd_intel_dspcfg rapl intel_cstate joydev snd_hda_codec mousedev intel_uncore snd_hwdep snd_hda_core psmouse snd_pcm snd_timer cfg80211 mei_me wacom ucsi_acpi typec_ucsi mei intel_pch_thermal intel_xhci_usb_role_switch intel_ish_ipc roles intel_ishtp typec wmi thinkpad_acpi ledtrig_audio platform_profile snd soundcore tpm_crb rfkill i2c_hid_acpi tpm_tis tpm_tis_core i2c_hid mac_hid acpi_pad pkcs8_key_parser fuse zram ip_tables x_tables ext4 crc32c_generic crc16 mbcache jbd2 usbhid dm_crypt cbc encrypted_keys trusted asn1_encoder tee tpm rng_core dm_mod rtsx_pci_sdmmc mmc_core serio_raw atkbd libps2 crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel crypto_simd cryptd rtsx_pci xhci_pci xhci_pci_renesas i8042 serio kvmgt mdev vfio_iommu_type1 vfio i915 i2c_algo_bit intel_gtt ttm agpgart video drm_kms_helper syscopyarea sysfillrect sysimgblt
> >  fb_sys_fops cec drm kvm irqbypass
> > CPU: 1 PID: 351 Comm: kworker/1:3 Not tainted 5.14.3 #1 c719caf0c6c208968387ed83e3061ac05d0faf2f
> > Workqueue: events free_user_ns
> > RIP: 0010:dec_ucount+0x43/0x50
> > Code: 14 01 48 8b 02 48 89 c6 48 83 ee 01 78 1c f0 48 0f b1 32 75 f0 48 8b 41 10 48 8b 88 e8 01 00 00 48 85 c9 75 d9 e9 0d fd ff ff <0f> 0b eb e7 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 f8 48
> > RSP: 0018:ffffaa06c08bbe60 EFLAGS: 00010297
> > RAX: 0000000000000000 RBX: ffff894ecb0c35a0 RCX: ffff894e25cdfcc0
> > RDX: ffff894e25cdfce0 RSI: ffffffffffffffff RDI: ffff894e25cdfcc0
> > RBP: ffff894ee393d380 R08: 0000000000000020 R09: ffff894ee393d5f0
> > R10: ffff894f617fd000 R11: 0000000000031678 R12: ffff894e25cdfcc0
> > R13: 00000000ffffffff R14: 0000000000000000 R15: 0000000000000001
> > FS:  0000000000000000(0000) GS:ffff894f59680000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 000056ffceff6b10 CR3: 0000000147a0e005 CR4: 00000000003706e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  free_user_ns+0x73/0x110
> >  process_one_work+0x1e1/0x380
> >  worker_thread+0x50/0x3a0
> >  ? rescuer_thread+0x360/0x360
> >  kthread+0x127/0x150
> >  ? set_kthread_struct+0x40/0x40
> >  ret_from_fork+0x22/0x30
> > ---[ end trace ff45ac39689f43c1 ]---
> > BUG: kernel NULL pointer dereference, address: 00000000000001e8
> > #PF: supervisor read access in kernel mode
> > #PF: error_code(0x0000) - not-present page
> > Oops: 0000 [#1] SMP PTI
> > CPU: 1 PID: 351 Comm: kworker/1:3 Tainted: G        W         5.14.3 #1 c719caf0c6c208968387ed83e3061ac05d0faf2f
> > Workqueue: events free_user_ns
> > RIP: 0010:dec_ucount+0x32/0x50
> > Code: 74 34 89 f6 48 89 f9 4c 8d 04 f5 20 00 00 00 4a 8d 14 01 48 8b 02 48 89 c6 48 83 ee 01 78 1c f0 48 0f b1 32 75 f0 48 8b 41 10 <48> 8b 88 e8 01 00 00 48 85 c9 75 d9 e9 0d fd ff ff 0f 0b eb e7 66
> > RSP: 0018:ffffaa06c08bbe60 EFLAGS: 00010297
> > RAX: 0000000000000000 RBX: ffff894ecb0c35a0 RCX: ffff894e25cdfcc0
> > RDX: ffff894e25cdfce0 RSI: ffffffffffffffff RDI: ffff894e25cdfcc0
> > RBP: ffff894ee393d380 R08: 0000000000000020 R09: ffff894ee393d5f0
> > R10: ffff894f617fd000 R11: 0000000000031678 R12: ffff894e25cdfcc0
> > R13: 00000000ffffffff R14: 0000000000000000 R15: 0000000000000001
> > FS:  0000000000000000(0000) GS:ffff894f59680000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00000000000001e8 CR3: 0000000147a0e005 CR4: 00000000003706e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  free_user_ns+0x73/0x110
> >  process_one_work+0x1e1/0x380
> >  worker_thread+0x50/0x3a0
> >  ? rescuer_thread+0x360/0x360
> >  kthread+0x127/0x150
> >  ? set_kthread_struct+0x40/0x40
> >  ret_from_fork+0x22/0x30
> > Modules linked in: nft_ct nft_fib_ipv4 nft_fib wireguard curve25519_x86_64 libcurve25519_generic libchacha20poly1305 chacha_x86_64 poly1305_x86_64 udp_tunnel libblake2s blake2s_x86_64 libblake2s_generic libchacha ccm algif_aead des_generic libdes ecb algif_skcipher cmac md4 algif_hash af_alg hid_sensor_custom_intel_hinge hid_sensor_als hid_sensor_gyro_3d hid_sensor_accel_3d hid_sensor_rotation hid_sensor_magn_3d hid_sensor_trigger industrialio_triggered_buffer hid_sensor_iio_common kfifo_buf industrialio hid_sensor_custom hid_sensor_hub cros_ec_ishtp cros_ec intel_ishtp_loader intel_ishtp_hid intel_rapl_msr nft_counter xt_mark ipt_REJECT nf_reject_ipv4 mei_hdcp intel_rapl_common xt_LOG nf_log_syslog intel_tcc_cooling x86_pkg_temp_thermal think_lmi wmi_bmof xt_addrtype firmware_attributes_class xt_tcpudp intel_powerclamp xt_conntrack nf_conntrack nf_defrag_ipv4 snd_hda_codec_hdmi nft_compat intel_wmi_thunderbolt nf_tables libcrc32c coretemp iwlmvm snd_ctl_led nfnetlink
> >  snd_hda_codec_conexant mac80211 snd_hda_codec_generic libarc4 vfat snd_hda_intel kvm_intel fat iwlwifi snd_intel_dspcfg rapl intel_cstate joydev snd_hda_codec mousedev intel_uncore snd_hwdep snd_hda_core psmouse snd_pcm snd_timer cfg80211 mei_me wacom ucsi_acpi typec_ucsi mei intel_pch_thermal intel_xhci_usb_role_switch intel_ish_ipc roles intel_ishtp typec wmi thinkpad_acpi ledtrig_audio platform_profile snd soundcore tpm_crb rfkill i2c_hid_acpi tpm_tis tpm_tis_core i2c_hid mac_hid acpi_pad pkcs8_key_parser fuse zram ip_tables x_tables ext4 crc32c_generic crc16 mbcache jbd2 usbhid dm_crypt cbc encrypted_keys trusted asn1_encoder tee tpm rng_core dm_mod rtsx_pci_sdmmc mmc_core serio_raw atkbd libps2 crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel crypto_simd cryptd rtsx_pci xhci_pci xhci_pci_renesas i8042 serio kvmgt mdev vfio_iommu_type1 vfio i915 i2c_algo_bit intel_gtt ttm agpgart video drm_kms_helper syscopyarea sysfillrect sysimgblt
> >  fb_sys_fops cec drm kvm irqbypass
> > CR2: 00000000000001e8
> > ---[ end trace ff45ac39689f43c2 ]---
> > RIP: 0010:dec_ucount+0x32/0x50
> > Code: 74 34 89 f6 48 89 f9 4c 8d 04 f5 20 00 00 00 4a 8d 14 01 48 8b 02 48 89 c6 48 83 ee 01 78 1c f0 48 0f b1 32 75 f0 48 8b 41 10 <48> 8b 88 e8 01 00 00 48 85 c9 75 d9 e9 0d fd ff ff 0f 0b eb e7 66
> > RSP: 0018:ffffaa06c08bbe60 EFLAGS: 00010297
> > RAX: 0000000000000000 RBX: ffff894ecb0c35a0 RCX: ffff894e25cdfcc0
> > RDX: ffff894e25cdfce0 RSI: ffffffffffffffff RDI: ffff894e25cdfcc0
> > RBP: ffff894ee393d380 R08: 0000000000000020 R09: ffff894ee393d5f0
> > R10: ffff894f617fd000 R11: 0000000000031678 R12: ffff894e25cdfcc0
> > R13: 00000000ffffffff R14: 0000000000000000 R15: 0000000000000001
> > FS:  0000000000000000(0000) GS:ffff894f59680000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00000000000001e8 CR3: 0000000147a0e005 CR4: 00000000003706e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 

-- 
Rgrds, legion