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 threadstruct of the associated task. These pointers are initially copied on fork() via archduptaskstruct() and then cleared via copythread() before fork() returns. If fork() happens to fail after the initial task dup and before copythread(), the newly allocated task and associated threadstruct memory are freed via freetask() -> archreleasetask_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 BUGON() in setfreepointer() (with CONFIGSLABFREELISTHARDENED enabled) or KASAN splat (if enabled) when running trinity syscall fuzz tests on s390x. To avoid this problem, clear the associated pointer fields in archduptaskstruct() 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.