iso9660.rs: added an error check

Added an incomplete file size error check to the ISO9660 parser.

src/iso9660.rs

@@ -49,6 +49,19 @@ pub struct IsoFs {
 impl IsoFs {
     pub fn from_file(mut file: fs::File) -> Result<Self> {
         let descriptors = get_volume_descriptors(&mut file)?;
+        match &descriptors[0] {
+            VolumeDescriptor::Boot(_boot_volume_descriptor) => {}
+            VolumeDescriptor::Primary(primary_volume_descriptor) => {
+                if i64::from(primary_volume_descriptor.volume_space_size)
+                    * i64::from(primary_volume_descriptor.logical_block_size)
+                    > file.metadata()?.len().try_into().unwrap()
+                {
+                    bail!("ISO Image is wrong and can't be modified");
+                }
+            }
+            VolumeDescriptor::Supplementary => {}
+            VolumeDescriptor::Unknown { type_id: _ } => {}
+        }
         Ok(Self { descriptors, file })
     }
 
@@ -181,6 +194,8 @@ struct BootVolumeDescriptor {
 struct PrimaryVolumeDescriptor {
     system_id: String,
     volume_id: String,
+    volume_space_size: i32,
+    logical_block_size: i16,
     root: Directory,
 }
 
@@ -298,13 +313,22 @@ impl PrimaryVolumeDescriptor {
             parse_iso9660_string(eat(buf, 1), 32, IsoString::StrA).context("parsing system id")?;
         let volume_id = // technically should be StrD, but non-compliance is common
             parse_iso9660_string(buf, 32, IsoString::StrA).context("parsing volume id")?;
-        let root = match get_next_directory_record(eat(buf, 156 - 72), 34, true)? {
+        eat(buf, 8); // Unused field always 0x00
+        let volume_space_size = // Data type: int32_LSB-MSB
+            buf.get_i32_le();
+        assert_eq!(volume_space_size, buf.get_i32());
+        eat(buf, 32 + 4 + 4); // Ignoring the following fields (Unused, Volume Set Size, Volume Sequence Number)
+        let logical_block_size = buf.get_i16_le();
+        assert_eq!(logical_block_size, buf.get_i16());
+        let root = match get_next_directory_record(eat(buf, 156 - 132), 34, true)? {
             Some(DirectoryRecord::Directory(d)) => d,
             _ => bail!("failed to parse root directory record from primary descriptor"),
         };
         Ok(Self {
             system_id,
             volume_id,
+            volume_space_size,
+            logical_block_size,
             root,
         })
     }