CVE-2022-49990

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

s390: fix double free of GS and RI CBs on fork() failure

The pointers for guarded storage and runtime instrumentation control

blocks are stored in the thread_struct of the associated task. These

pointers are initially copied on fork() via arch_dup_task_struct()

and then cleared via copy_thread() before fork() returns. If fork()

happens to fail after the initial task dup and before copy_thread(),

the newly allocated task and associated thread_struct memory are

freed via free_task() -> arch_release_task_struct(). This results in

a double free of the guarded storage and runtime info structs

because the fields in the failed task still refer to memory

associated with the source task.

This problem can manifest as a BUG_ON() in set_freepointer() (with

CONFIG_SLAB_FREELIST_HARDENED enabled) or KASAN splat (if enabled)

when running trinity syscall fuzz tests on s390x. To avoid this

problem, clear the associated pointer fields in

arch_dup_task_struct() immediately after the new task is copied.

Note that the RI flag is still cleared in copy_thread() because it

resides in thread stack memory and that is where stack info is

copied.