CVE-2022-50095

In the Linux kernel, the following vulnerability has been resolved:

posix-cpu-timers: Cleanup CPU timers before freeing them during exec

Commit 55e8c8eb2c7b (posix-cpu-timers: Store a reference to a pid not a task) started looking up tasks by PID when deleting a CPU timer.

When a non-leader thread calls execve, it will switch PIDs with the leader process. Then, as it calls exit_itimers, posix_cpu_timer_del cannot find the task because the timer still points out to the old PID.

That means that armed timers wont be disarmed, that is, they wont be removed from the timerqueue_list. exit_itimers will still release their memory, and when that list is later processed, it leads to a use-after-free.

Clean up the timers from the de-threaded task before freeing them. This prevents a reported use-after-free.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/541840859ace9c2ccebc32fa9e376c7bd3def490
• https://git.kernel.org/stable/c/9e255ed238fc67058df87b0388ad6d4b2ef3a2bd
• https://git.kernel.org/stable/c/b2fc1723eb65abb83e00d5f011de670296af0b28
• https://git.kernel.org/stable/c/e362359ace6f87c201531872486ff295df306d13
• https://git.kernel.org/stable/c/e8cb6e8fd9890780f1bfcf5592889e1b879e779c