tty: tty_buffer: Fix the softlockup issue in flush_to_ldisc
Key facts
- Attack vector
- Local
- Privileges required
- High
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Partial Red Hat: 14 fixed, 1 without a fix
Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA and Red Hat. Impact type from CWE-667 and the CVSS impact.
Summary
In the Linux kernel, the following vulnerability has been resolved: tty: tty_buffer: Fix the softlockup issue in flush_to_ldisc When running ltp testcase(ltp/testcases/kernel/pty/pty04.c) with arm64, there is a soft lockup, which look like this one: Workqueue: events_unbound flush_to_ldisc Call trace: dump_backtrace+0x0/0x1ec show_stack+0x24/0x30 dump_stack+0xd0/0x128 panic+0x15c/0x374 watchdog_timer_fn+0x2b8/0x304 __run_hrtimer+0x88/0x2c0 __hrtimer_run_queues+0xa4/0x120 hrtimer_interrupt+0xfc/0x270 arch_timer_handler_phys+0x40/0x50 handle_percpu_devid_irq+0x94/0x220 __handle_domain_irq+0x88/0xf0 gic_handle_irq+0x84/0xfc el1_irq+0xc8/0x180 slip_unesc+0x80/0x214 [slip] tty_ldisc_receive_buf+0x64/0x80 tty_port_default_receive_buf+0x50/0x90 flush_to_ldisc+0xbc/0x110 process_one_work+0x1d4/0x4b0 worker_thread+0x180/0x430 kthread+0x11c/0x120 In the testcase pty04, The first process call the write syscall to send data to the pty master. At the same time, the workqueue will do the flush_to_ldisc to pop data in a loop until there is no more data left. When the sender and workqueue running in different core, the sender sends data fastly in full time which will result in workqueue doing work in loop for a long time and occuring softlockup in flush_to_ldisc with kernel configured without preempt. So I add need_resched check and cond_resched in the flush_to_ldisc loop to avoid it.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Linux | Linux | 3.0 and later | 4.4.293, 4.9.291, 4.14.256, 4.19.218, 5.4.162, 5.10.82, 5.15.5, 5.16 | Patch available | CNA |
- Linux VendorLinux Affected 3.0 and later Fixed in 4.4.293, 4.9.291, 4.14.256, 4.19.218, 5.4.162, 5.10.82, 5.15.5, 5.16 Patch available CNA
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | before 4.4.293; 4.5 to before 4.9.291; 4.10 to before 4.14.256; 4.15 to before 4.19.218; 4.20 to before 5.4.162; 5.5 to before 5.10.82; 5.11 to before 5.15.5 | Vulnerable | Linux |
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* Versions before 4.4.293; 4.5 to before 4.9.291; 4.10 to before 4.14.256; 4.15 to before 4.19.218; 4.20 to before 5.4.162; 5.5 to before 5.10.82; 5.11 to before 5.15.5 Vulnerable ·Linux
Remediation
- Fix · CNA Linux (Linux) Fixed in 4.4.293, 4.9.291, 4.14.256, 4.19.218, 5.4.162, 5.10.82, 5.15.5, 5.16
Red Hat 4 advisories
- RHSA-2025:11810 Released 2025-07-28 · Red Hat rating Importantkernel security update
- Red Hat CodeReady Linux Builder EUS (v.9.4) kernel-tools-libs-devel-5.14.0-427.79.1.el9_4, libperf-5.14.0-427.79.1.el9_4
- Red Hat Enterprise Linux AppStream EUS (v.9.4) kernel-64k-debug-devel-5.14.0-427.79.1.el9_4, kernel-64k-debug-devel-matched-5.14.0-427.79.1.el9_4, kernel-64k-devel-5.14.0-427.79.1.el9_4 +11
- Red Hat Enterprise Linux BaseOS EUS (v.9.4) bpftool-7.3.0-427.79.1.el9_4, kernel-5.14.0-427.79.1.el9_4, kernel-64k-5.14.0-427.79.1.el9_4 +29
- Red Hat Enterprise Linux Real Time EUS (v.9.4) kernel-rt-5.14.0-427.79.1.el9_4, kernel-rt-core-5.14.0-427.79.1.el9_4, kernel-rt-debug-5.14.0-427.79.1.el9_4 +9
- Red Hat Enterprise Linux Real Time for NFV EUS (v.9.4) kernel-rt-5.14.0-427.79.1.el9_4, kernel-rt-core-5.14.0-427.79.1.el9_4, kernel-rt-debug-5.14.0-427.79.1.el9_4 +11
- RHSA-2024:9315 Released 2024-11-12 · Red Hat rating Moderatekernel security update
- Red Hat CodeReady Linux Builder (v. 9) kernel-cross-headers-5.14.0-503.11.1.el9_5, kernel-tools-libs-devel-5.14.0-503.11.1.el9_5, libperf-5.14.0-503.11.1.el9_5
- Red Hat Enterprise Linux AppStream (v. 9) kernel-64k-debug-devel-5.14.0-503.11.1.el9_5, kernel-64k-debug-devel-matched-5.14.0-503.11.1.el9_5, kernel-64k-devel-5.14.0-503.11.1.el9_5 +12
- Red Hat Enterprise Linux BaseOS (v. 9) bpftool-7.4.0-503.11.1.el9_5, kernel-5.14.0-503.11.1.el9_5, kernel-64k-5.14.0-503.11.1.el9_5 +30
- Red Hat Enterprise Linux Real Time (v. 9) kernel-rt-5.14.0-503.11.1.el9_5, kernel-rt-core-5.14.0-503.11.1.el9_5, kernel-rt-debug-5.14.0-503.11.1.el9_5 +9
- Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt-5.14.0-503.11.1.el9_5, kernel-rt-core-5.14.0-503.11.1.el9_5, kernel-rt-debug-5.14.0-503.11.1.el9_5 +11
- RHSA-2024:3627 Released 2024-06-05 · Red Hat rating Moderatekernel-rt security and bug fix update
- Red Hat Enterprise Linux NFV (v. 8) kernel-rt-4.18.0-553.5.1.rt7.346.el8_10, kernel-rt-core-4.18.0-553.5.1.rt7.346.el8_10, kernel-rt-debug-4.18.0-553.5.1.rt7.346.el8_10 +9
- Red Hat Enterprise Linux RT (v. 8) kernel-rt-4.18.0-553.5.1.rt7.346.el8_10, kernel-rt-core-4.18.0-553.5.1.rt7.346.el8_10, kernel-rt-debug-4.18.0-553.5.1.rt7.346.el8_10 +7
Show 1 more Red Hat advisories
- RHSA-2024:3618 Released 2024-06-05 · Red Hat rating Moderatekernel update
- Red Hat Enterprise Linux BaseOS (v. 8) bpftool-4.18.0-553.5.1.el8_10, kernel-4.18.0-553.5.1.el8_10, kernel-abi-stablelists-4.18.0-553.5.1.el8_10 +19
- Red Hat Enterprise Linux CRB (v. 8) kernel-tools-libs-devel-4.18.0-553.5.1.el8_10
Vendor assessments
Red Hat
Red Hat rating: Low. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Out of support scope |
| Red Hat CodeReady Linux Builder (v. 9) | Fixed | RHSA-2024:9315 |
| Red Hat CodeReady Linux Builder EUS (v.9.4) | Fixed | RHSA-2025:11810 |
| Red Hat Enterprise Linux AppStream (v. 9) | Fixed | RHSA-2024:9315 |
| Red Hat Enterprise Linux AppStream EUS (v.9.4) | Fixed | RHSA-2025:11810 |
| Red Hat Enterprise Linux BaseOS (v. 8) | Fixed | RHSA-2024:3618 |
| Red Hat Enterprise Linux BaseOS (v. 9) | Fixed | RHSA-2024:9315 |
| Red Hat Enterprise Linux BaseOS EUS (v.9.4) | Fixed | RHSA-2025:11810 |
| Red Hat Enterprise Linux CRB (v. 8) | Fixed | RHSA-2024:3618 |
| Red Hat Enterprise Linux NFV (v. 8) | Fixed | RHSA-2024:3627 |
| Red Hat Enterprise Linux RT (v. 8) | Fixed | RHSA-2024:3627 |
| Red Hat Enterprise Linux Real Time (v. 9) | Fixed | RHSA-2024:9315 |
| Red Hat Enterprise Linux Real Time EUS (v.9.4) | Fixed | RHSA-2025:11810 |
| Red Hat Enterprise Linux Real Time for NFV (v. 9) | Fixed | RHSA-2024:9315 |
| Red Hat Enterprise Linux Real Time for NFV EUS (v.9.4) | Fixed | RHSA-2025:11810 |
Not affected: 3 products
- Red Hat CodeReady Linux Builder (v. 9)
- Red Hat Enterprise Linux 6
- Red Hat Enterprise Linux AppStream (v. 9)
Timeline
- 2026-10-02 Threatist record created from CVE-2021-47185
- 2026-10-03 Alias added: GHSA-gvxc-64wh-vgv2
- 2026-10-29 Affected versions changed · Red Hat
References
Patch 8
- https://git.kernel.org/stable/c/0380f643f3a7a61b0845cdc738959c2ad5735d61
- https://git.kernel.org/stable/c/b1ffc16ec05ae40d82b6e373322d62e9d6b54fbc
- https://git.kernel.org/stable/c/4c1623651a0936ee197859824cdae6ebbd04d3ed
- https://git.kernel.org/stable/c/4f300f47dbcf9c3d4b2ea76c8554c8f360400725
- https://git.kernel.org/stable/c/d491c84df5c469dd9621863b6a770b3428137063
- https://git.kernel.org/stable/c/77e9fed33056f2a88eba9dd4d2d5412f0c7d1f41
- https://git.kernel.org/stable/c/5c34486f04700f1ba04907231dce0cc2705c2d7d
- https://git.kernel.org/stable/c/3968ddcf05fb4b9409cd1859feb06a5b0550a1c1
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- TI-2021-05514 Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE KEVCVSS 3.1HIGH 8.3
Sources
- CVE-2021-47185 · CVE Program
- CVE-2021-47185 · NVD
- FIRST EPSS
- GHSA-gvxc-64wh-vgv2 · GitHub Advisory Database · CC BY 4.0
- CVE-2021-47185 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences