Re: linux 5.14.3: free_user_ns causes NULL pointer dereference

[ebiederm@xmission.com (Eric W. Biederman)]

Jordan Glover <Golden_Miller83@protonmail.ch> writes:

> Hi, recently I hit system freeze after I was closing few containerized apps on my system. As for now it occurred only once on linux 5.14.3. I think it maybe be related to "Count rlimits in each user namespace" patchset merged during 5.14 window
>
> https://lore.kernel.org/all/257aa5fb1a7d81cf0f4c34f39ada2320c4284771.1619094428.git.legion@kernel.org/T/#u

So that warning comes from:

void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
{
	struct ucounts *iter;
	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
		long dec = atomic_long_dec_if_positive(&iter->ucount[type]);
		WARN_ON_ONCE(dec < 0);
	}
	put_ucounts(ucounts);
}

Which certainly looks like a reference count bug.  It could also be a
memory stomp somewhere close.

Do you have any idea what else was going on?  This location is the
symptom but not the actual cause.

Eric



>
> Logs below:
>
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 26546 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_magn_3d hid_sensor_rotation hid_sensor_accel_3d hid_sensor_gyro_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 nft_counter intel_ishtp_hid snd_hda_codec_hdmi intel_rapl_msr xt_mark ipt_REJECT nf_reject_ipv4 snd_ctl_led xt_LOG snd_hda_codec_conexant nf_log_syslog snd_hda_codec_generic xt_addrtype xt_tcpudp xt_conntrack nf_conntrack nf_defrag_ipv4 mei_hdcp snd_hda_intel nft_compat wmi_bmof nf_tables intel_rapl_common libcrc32c think_lmi intel_tcc_cooling snd_intel_dspcfg firmware_attributes_class nfnetlink iwlmvm
>  intel_wmi_thunderbolt mac80211 x86_pkg_temp_thermal snd_hda_codec intel_powerclamp coretemp libarc4 vfat fat kvm_intel rapl intel_cstate snd_hwdep intel_uncore iwlwifi snd_hda_core mousedev joydev snd_pcm psmouse cfg80211 snd_timer mei_me ucsi_acpi wacom intel_ish_ipc intel_xhci_usb_role_switch mei intel_pch_thermal typec_ucsi roles typec intel_ishtp wmi thinkpad_acpi ledtrig_audio platform_profile snd soundcore rfkill tpm_crb i2c_hid_acpi i2c_hid acpi_pad tpm_tis mac_hid tpm_tis_core 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 xhci_pci rtsx_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: 26546 Comm: kworker/1:1 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:ffffa82cc2bd7e60 EFLAGS: 00010297
> RAX: 0000000000000000 RBX: ffffa2f53298ee50 RCX: ffffa2f3c0061000
> RDX: ffffa2f3c0061020 RSI: ffffffffffffffff RDI: ffffa2f3c0061000
> RBP: ffffa2f53298ebe0 R08: 0000000000000020 R09: 0000000000000000
> R10: 0000000000000001 R11: 0000000000000000 R12: ffffa2f3c0061000
> R13: 00000000ffffffff R14: 0000000000000000 R15: 0000000000000001
> FS:  0000000000000000(0000) GS:ffffa2f599680000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000628f892be9f8 CR3: 000000002880e004 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 eb7a8d38b64b2d3a ]---
> 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: 26546 Comm: kworker/1:1 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:ffffa82cc2bd7e60 EFLAGS: 00010297
> RAX: 0000000000000000 RBX: ffffa2f53298ee50 RCX: ffffa2f3c0061000
> RDX: ffffa2f3c0061020 RSI: ffffffffffffffff RDI: ffffa2f3c0061000
> RBP: ffffa2f53298ebe0 R08: 0000000000000020 R09: 0000000000000000
> R10: 0000000000000001 R11: 0000000000000000 R12: ffffa2f3c0061000
> R13: 00000000ffffffff R14: 0000000000000000 R15: 0000000000000001
> FS:  0000000000000000(0000) GS:ffffa2f599680000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000000001e8 CR3: 000000002880e004 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