CVE-2022-50206

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

arm64: fix oops in concurrently setting insn_emulation sysctls

emulation_proc_handler() changes table->data for proc_dointvec_minmax

and can generate the following Oops if called concurrently with itself:

| Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010

| Internal error: Oops: 96000006 [#1] SMP

| Call trace:

| update_insn_emulation_mode+0xc0/0x148

| emulation_proc_handler+0x64/0xb8

| proc_sys_call_handler+0x9c/0xf8

| proc_sys_write+0x18/0x20

| __vfs_write+0x20/0x48

| vfs_write+0xe4/0x1d0

| ksys_write+0x70/0xf8

| __arm64_sys_write+0x20/0x28

| el0_svc_common.constprop.0+0x7c/0x1c0

| el0_svc_handler+0x2c/0xa0

| el0_svc+0x8/0x200

To fix this issue, keep the table->data as &insn->current_mode and

use container_of() to retrieve the insn pointer. Another mutex is

used to protect against the current_mode update but not for retrieving

insn_emulation as table->data is no longer changing.