CVE-2025-40201: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability has been identified in the Linux kernel (CVE-2025-40201) related to the racy usage of tasklock(tsk->groupleader) in sys_prlimit64() paths. The issue was discovered and published to the CVE List on November 12, 2025 (NVD).

The vulnerability exists in kernel/sys.c where the usage of tasklock(tsk->groupleader) in sysprlimit64()->doprlimit() path is broken. While sysprlimit64() obtains gettaskstruct(tsk), this only protects the taskstruct itself. When tsk is not the current task and not a leader, the process can exit/exec, potentially leading to the use of an already freed taskstruct. Additionally, sysprlimit64() can race with mt-exec which modifies ->groupleader, potentially resulting in taking the wrong lock or having ->groupleader change between tasklock() and taskunlock() (NVD).

If exploited, this vulnerability could lead to use-after-free conditions and race conditions in the Linux kernel's process limit handling functionality, potentially affecting system stability and security (NVD).

The fix involves modifying sysprlimit64() to take tasklistlock when necessary. While this solution is noted as not being optimal, it has been implemented as the best available fix for stable kernel versions (NVD).