sgdisk: add blk_file ioctls

Add support for the HDIO_GETGEO and BLKGETSIZE ioctls when operating on
/dev/block/vold/ block devices.

HDIO_GETGEO is needed by the sgdisk code to get the number of heads on
the disk drive, likely a side effect of the age of this code.
https://android.googlesource.com/platform/external/gptfdisk/+/646af625ced09e5d81e07fe8c02c32017e3cbc07/diskio-unix.cc#193

Addresses the following denial:
  audit(0.0:1775): avc: denied { ioctl } for comm="sgdisk" path="/dev/block/vold/disk:8,96" dev="tmpfs" ino=10740855 ioctlcmd=0x301 scontext=u:r:sgdisk:s0 tcontext=u:object_r:vold_device:s0 tclass=blk_file permissive=0

BLKGETSIZE is used to determine the size of the block device. Ideally
code should not be using this ioctl, as it fails for devices >= 2T in
size. Technically we don't need to grant this, as the sgdisk code will
fall back to using BLKGETSIZE64 if BLKGETSIZE fails.
https://android.googlesource.com/platform/external/gptfdisk/+/646af625ced09e5d81e07fe8c02c32017e3cbc07/diskio-unix.cc#430

Addresses the following denial:
  audit(0.0:1778): avc: denied { ioctl } for comm="sgdisk" path="/dev/block/vold/disk:8,96" dev="tmpfs" ino=10740855 ioctlcmd=0x1260 scontext=u:r:sgdisk:s0 tcontext=u:object_r:vold_device:s0 tclass=blk_file permissive=0

Test: policy compiles.
Change-Id: Iaa5274721e8a7d1741591570e9e5305723aad640

public/sgdisk.te

@@ -5,6 +5,16 @@ type sgdisk_exec, system_file_type, exec_type, file_type;
 # Allowed to read/write low-level partition tables
 allow sgdisk block_device:dir search;
 allow sgdisk vold_device:blk_file rw_file_perms;
+# HDIO_GETGEO needed to get the number of disk heads
+# on vold_device. How quaint.
+allowxperm sgdisk vold_device:blk_file ioctl { HDIO_GETGEO };
+# sgdisk also uses BLKGETSIZE and BLKGETSIZE64. BLKGETSIZE64
+# is granted to all block device users in domain.te, so
+# no need to mention it here. sgdisk should not be
+# using the BLKGETSIZE ioctl as it is useless for devices over
+# 2T in size, but we allow it for now and hope that sgdisk
+# will fix their bug.
+allowxperm sgdisk vold_device:blk_file ioctl { BLKGETSIZE };
 
 # Inherit and use pty created by android_fork_execvp()
 allow sgdisk devpts:chr_file { read write ioctl getattr };