CVE-2021-47185

MEDIUM
Published Apr 10, 2024 Modified Mar 21, 2025 CWE-667

Description

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.

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CVSS v3.1 Score

4.4
MEDIUM
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-667 CWE-667

Affected Products

Vendor Product
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel

References

Advisories & Patches

https://git.kernel.org/stable/c/0380f643f3a7a61b0845cdc738959c2ad5735d61 https://git.kernel.org/stable/c/3968ddcf05fb4b9409cd1859feb06a5b0550a1c1 https://git.kernel.org/stable/c/4c1623651a0936ee197859824cdae6ebbd04d3ed https://git.kernel.org/stable/c/4f300f47dbcf9c3d4b2ea76c8554c8f360400725 https://git.kernel.org/stable/c/5c34486f04700f1ba04907231dce0cc2705c2d7d https://git.kernel.org/stable/c/77e9fed33056f2a88eba9dd4d2d5412f0c7d1f41 https://git.kernel.org/stable/c/b1ffc16ec05ae40d82b6e373322d62e9d6b54fbc https://git.kernel.org/stable/c/d491c84df5c469dd9621863b6a770b3428137063 https://git.kernel.org/stable/c/0380f643f3a7a61b0845cdc738959c2ad5735d61 https://git.kernel.org/stable/c/3968ddcf05fb4b9409cd1859feb06a5b0550a1c1 https://git.kernel.org/stable/c/4c1623651a0936ee197859824cdae6ebbd04d3ed https://git.kernel.org/stable/c/4f300f47dbcf9c3d4b2ea76c8554c8f360400725 https://git.kernel.org/stable/c/5c34486f04700f1ba04907231dce0cc2705c2d7d https://git.kernel.org/stable/c/77e9fed33056f2a88eba9dd4d2d5412f0c7d1f41 https://git.kernel.org/stable/c/b1ffc16ec05ae40d82b6e373322d62e9d6b54fbc https://git.kernel.org/stable/c/d491c84df5c469dd9621863b6a770b3428137063

Frequently Asked Questions

What is CVE-2021-47185? +
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. It has a CVSS v3.1 base score of 4.4 (MEDIUM).
How severe is CVE-2021-47185? +
CVE-2021-47185 has a CVSS v3.1 score of 4.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.
What products are affected by CVE-2021-47185? +
CVE-2021-47185 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.
How do I check if I'm vulnerable to CVE-2021-47185? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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