tee: add overflow check in register_shm_helper()
In the Linux kernel, the following vulnerability has been resolved:

tee: add overflow check in register_shm_helper()

With special lengths supplied by user space, register_shm_helper() has
an integer overflow when calculating the number of pages covered by a
supplied user space memory region.

This causes internal_get_user_pages_fast() a helper function of
pin_user_pages_fast() to do a NULL pointer dereference:

  Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
  Modules linked in:
  CPU: 1 PID: 173 Comm: optee_example_a Not tainted 5.19.0 #11
  Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
  pc : internal_get_user_pages_fast+0x474/0xa80
  Call trace:
   internal_get_user_pages_fast+0x474/0xa80
   pin_user_pages_fast+0x24/0x4c
   register_shm_helper+0x194/0x330
   tee_shm_register_user_buf+0x78/0x120
   tee_ioctl+0xd0/0x11a0
   __arm64_sys_ioctl+0xa8/0xec
   invoke_syscall+0x48/0x114

Fix this by adding an an explicit call to access_ok() in
tee_shm_register_user_buf() to catch an invalid user space address
early.