[Libguestfs] [PATCH] daemon: inspect: better handling windows drive mapping.

[Mykola Ivanets]

I have several Windows disk images which contains strange registry entry
for mapped drives:

"\\DosDevices\\Y:"=hex(3):00,00,00,00,00,00,00,00,00,00,00,00

Which is decoded something like diskID = 0x0, partition starts at
0 bytes from the start of the disk.  In addition of Windows disk image
I have attached dummy disk and made xfs file system on a whole device
without partitioning it.  I mount xfs file system to a "/" and then
mount other found file systems inside (/fs1, /fs2 etc.).  When we decode
drive mappings we are looking for a disk with ID 0x0 (it is 4 bytes
somewhere LBA0).  It is appeared that dummy non-partitioned disk with
xfs file system has zeros by offset where diskID is expected to be).
So the disk is considered as a candidate to search for partition at
offset 0.  part-list command (and "parted" which is used under the hood)
reports there is 1 partition on "dummy" disk which starts exactly at
offset 0.  And thus dummy device name and partition number are simply
concatenated together and corresponding drive mapping is returned:
Y => /dev/sdX1.  But /dev/sdX1 is not existing block device.

No matter either it is a bug in "parted" (or it works a such by-design),
let's protect ourself from this situation: in addition we look for msdos
partition table on a disk before making any further assumptions.
---
 daemon/inspect_fs_windows.ml | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/daemon/inspect_fs_windows.ml b/daemon/inspect_fs_windows.ml
index 8b2aad8d3..af52dee2d 100644
--- a/daemon/inspect_fs_windows.ml
+++ b/daemon/inspect_fs_windows.ml
@@ -329,7 +329,7 @@ and get_drive_mappings h root data =
                    String.is_prefix blob "DMIO:ID:" (* GPT *) then
                   map_registry_disk_blob_gpt (Lazy.force partitions) blob
                 else if String.length blob = 12 then
-                  map_registry_disk_blob (Lazy.force devices) blob
+                  map_registry_disk_blob_mbr (Lazy.force devices) blob
                 else
                   None
               )
@@ -356,13 +356,18 @@ and get_drive_mappings h root data =
  * The following function maps this blob to a libguestfs partition
  * name, if possible.
  *)
-and map_registry_disk_blob devices blob =
+and map_registry_disk_blob_mbr devices blob =
   try
     (* First 4 bytes are the disk ID.  Search all devices to find the
      * disk with this disk ID.
      *)
     let diskid = String.sub blob 0 4 in
-    let device = List.find (fun dev -> pread dev 4 0x01b8 = diskid) devices in
+    let device =
+      List.find (
+        fun dev ->
+          Parted.part_get_parttype dev = "msdos" &&
+            pread dev 4 0x01b8 = diskid
+      ) devices in
 
     (* Next 8 bytes are the offset of the partition in bytes(!) given as
      * a 64 bit little endian number.  Luckily it's easy to get the
-- 
2.17.0