Re: [BUG][5.20] refcount_t: underflow; use-after-free

[Melissa Wen]

On 08/17, Mikhail Gavrilov wrote:
> On Mon, Aug 15, 2022 at 3:37 PM Mikhail Gavrilov
> <mikhail.v.gavrilov@xxxxxxxxx> wrote:
> >
> > Thanks, I tested this patch.
> > But with this patch use-after-free problem happening in another place:
> 
> Does anyone have an idea why the second use-after-free happened?
> From the trace I don't understand which code is related.
> I don't quite understand what the "Workqueue" entry in the trace means.

Hi Mikhail,

IIUC, you got this second user-after-free by applying the first version
of Maíra's patch, right? So, that version was adding another unbalanced
unlock to the cs ioctl flow, but it was solved in the latest version,
that you can find here: https://patchwork.freedesktop.org/patch/497680/
If this is the situation, can you check this last version?

Thanks,

Melissa

> 
> [ 408.358737] ------------[ cut here ]------------
> [ 408.358743] refcount_t: underflow; use-after-free.
> [ 408.358760] WARNING: CPU: 9 PID: 62 at lib/refcount.c:28
> refcount_warn_saturate+0xba/0x110
> [ 408.358769] Modules linked in: uinput snd_seq_dummy rfcomm
> snd_hrtimer nft_objref nf_conntrack_netbios_ns nf_conntrack_broadcast
> nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet
> nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat
> nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nf_tables nfnetlink
> qrtr bnep sunrpc binfmt_misc snd_seq_midi snd_seq_midi_event mt76x2u
> mt76x2_common snd_hda_codec_realtek mt76x02_usb snd_hda_codec_generic
> iwlmvm snd_hda_codec_hdmi mt76_usb intel_rapl_msr snd_hda_intel
> mt76x02_lib intel_rapl_common snd_intel_dspcfg snd_intel_sdw_acpi mt76
> snd_hda_codec vfat fat snd_usb_audio snd_hda_core edac_mce_amd
> mac80211 snd_usbmidi_lib snd_hwdep snd_rawmidi mc snd_seq btusb
> kvm_amd iwlwifi snd_seq_device btrtl btbcm libarc4 btintel eeepc_wmi
> snd_pcm iwlmei kvm btmtk asus_wmi ledtrig_audio irqbypass joydev
> snd_timer sparse_keymap bluetooth platform_profile rapl cfg80211 snd
> video wmi_bmof soundcore i2c_piix4 k10temp rfkill mei
> [ 408.358853] asus_ec_sensors acpi_cpufreq zram hid_logitech_hidpp
> amdgpu igb dca drm_ttm_helper ttm iommu_v2 crct10dif_pclmul gpu_sched
> crc32_pclmul ucsi_ccg crc32c_intel drm_buddy nvme typec_ucsi
> drm_display_helper ghash_clmulni_intel ccp typec nvme_core sp5100_tco
> cec wmi ip6_tables ip_tables fuse
> [ 408.358880] Unloaded tainted modules: amd64_edac():1 amd64_edac():1
> amd64_edac():1 amd64_edac():1 amd64_edac():1 amd64_edac():1
> amd64_edac():1 amd64_edac():1 amd64_edac():1 amd64_edac():1
> pcc_cpufreq():1 amd64_edac():1 pcc_cpufreq():1 pcc_cpufreq():1
> amd64_edac():1 amd64_edac():1 pcc_cpufreq():1 amd64_edac():1
> pcc_cpufreq():1 amd64_edac():1 pcc_cpufreq():1 amd64_edac():1
> pcc_cpufreq():1 pcc_cpufreq():1 amd64_edac():1 pcc_cpufreq():1
> amd64_edac():1 pcc_cpufreq():1 amd64_edac():1 pcc_cpufreq():1
> pcc_cpufreq():1 amd64_edac():1 amd64_edac():1 pcc_cpufreq():1
> pcc_cpufreq():1 amd64_edac():1 pcc_cpufreq():1 amd64_edac():1
> pcc_cpufreq():1 amd64_edac():1 pcc_cpufreq():1 pcc_cpufreq():1
> amd64_edac():1 pcc_cpufreq():1 amd64_edac():1 pcc_cpufreq():1
> amd64_edac():1 pcc_cpufreq():1 pcc_cpufreq():1 amd64_edac():1
> pcc_cpufreq():1 amd64_edac():1 amd64_edac():1 pcc_cpufreq():1
> amd64_edac():1 pcc_cpufreq():1 amd64_edac():1 pcc_cpufreq():1
> pcc_cpufreq():1 pcc_cpufreq():1 fjes():1 pcc_cpufreq():1 fjes():1
> [ 408.358953] pcc_cpufreq():1 pcc_cpufreq():1 fjes():1 pcc_cpufreq():1
> fjes():1 fjes():1 fjes():1 fjes():1 fjes():1
> [ 408.358967] CPU: 9 PID: 62 Comm: kworker/9:0 Tainted: G W L -------
> --- 6.0.0-0.rc1.13.fc38.x86_64+debug #1
> [ 408.358971] Hardware name: System manufacturer System Product
> Name/ROG STRIX X570-I GAMING, BIOS 4403 04/27/2022
> [ 408.358974] Workqueue: events drm_sched_entity_kill_jobs_work [gpu_sched]
> [ 408.358982] RIP: 0010:refcount_warn_saturate+0xba/0x110
> [ 408.358987] Code: 01 01 e8 d9 59 6f 00 0f 0b e9 a2 46 a5 00 80 3d 3e
> 7e be 01 00 75 85 48 c7 c7 70 99 8e 92 c6 05 2e 7e be 01 01 e8 b6 59
> 6f 00 <0f> 0b e9 7f 46 a5 00 80 3d 19 7e be 01 00 0f 85 5e ff ff ff 48
> c7
> [ 408.358990] RSP: 0018:ffffb124003efe60 EFLAGS: 00010286
> [ 408.358994] RAX: 0000000000000026 RBX: ffff9987a025d428 RCX: 0000000000000000
> [ 408.358997] RDX: 0000000000000001 RSI: ffffffff928d0754 RDI: 00000000ffffffff
> [ 408.358999] RBP: ffff9994e4ff5600 R08: 0000000000000000 R09: ffffb124003efd10
> [ 408.359001] R10: 0000000000000003 R11: ffff99952e2fffe8 R12: ffff9994e4ffc800
> [ 408.359004] R13: ffff998600228cc0 R14: ffff9994e4ffc805 R15: ffff9987a025d430
> [ 408.359006] FS: 0000000000000000(0000) GS:ffff9994e4e00000(0000)
> knlGS:0000000000000000
> [ 408.359009] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 408.359012] CR2: 000027ac39e78000 CR3: 00000001a66d8000 CR4: 0000000000350ee0
> [ 408.359015] Call Trace:
> [ 408.359017] <TASK>
> [ 408.359020] process_one_work+0x2a0/0x600
> [ 408.359032] worker_thread+0x4f/0x3a0
> [ 408.359036] ? process_one_work+0x600/0x600
> [ 408.359039] kthread+0xf5/0x120
> [ 408.359044] ? kthread_complete_and_exit+0x20/0x20
> [ 408.359049] ret_from_fork+0x22/0x30
> [ 408.359061] </TASK>
> [ 408.359063] irq event stamp: 5468
> [ 408.359064] hardirqs last enabled at (5467): [<ffffffff91f2b9e4>]
> _raw_spin_unlock_irq+0x24/0x50
> [ 408.359071] hardirqs last disabled at (5468): [<ffffffff91f22d8c>]
> __schedule+0xe2c/0x16d0
> [ 408.359076] softirqs last enabled at (2482): [<ffffffff917acc28>]
> rht_deferred_worker+0x708/0xc00
> [ 408.359079] softirqs last disabled at (2480): [<ffffffff917ac717>]
> rht_deferred_worker+0x1f7/0xc00
> [ 408.359082] ---[ end trace 0000000000000000 ]---
> 
> 
> Full kernel log is here: https://pastebin.com/Lam9CRLV
> 
> -- 
> Best Regards,
> Mike Gavrilov.

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