CVE-2021-47185: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47185 is a vulnerability in the Linux kernel's TTY subsystem, specifically in the flush_to_ldisc function of the tty_buffer component. The vulnerability was discovered when running LTP (Linux Test Project) testcase pty04 on ARM64 architecture, where a soft lockup condition could occur (Kernel Git).

The issue occurs in the flush_to_ldisc function when handling data transfer between a PTY master and its workqueue. When the sender and workqueue are running on different CPU cores, and the sender is continuously sending data at a high rate, the workqueue can enter a loop that processes data without yielding, leading to a soft lockup condition in systems configured without preemption. The vulnerability was fixed by adding scheduling point checks (need_resched) and implementing conditional rescheduling (cond_resched) in the flush_to_ldisc loop (Kernel Git).

The vulnerability can cause system soft lockups when a process is continuously writing data to a PTY master device while the workqueue is processing the data on a different CPU core. This primarily affects systems running without preemption enabled and can lead to system responsiveness issues or potential denial of service conditions (Kernel Git).

The vulnerability can be triggered through normal system operations when using PTY devices with specific workload patterns. It was initially discovered through the Linux Test Project's pty04 test case, suggesting it can be reliably reproduced under controlled conditions (Kernel Git).

The fix has been implemented in the Linux kernel by adding scheduling checks in the flush_to_ldisc loop. The patch adds need_resched() checks and cond_resched() calls to allow other tasks to run when necessary. Users should update to patched kernel versions that include this fix (Red Hat).