chroe: properly perform checksums on partition table arrays

Some partitioning tools like ones based on libparted (parted and
GParted) don't wipe the entire GPT partition name field before writing
new partition names. Additionally, it is not guaranteed to be properly
zeroed since the UEFI specification does not clearly state that.

Use a dedicated raw buffer holding the entire partition name field
without any conversion for performing checksums and serializations.

Signed-off-by: Xinhui Yang <[email protected]>

Author: Cyanoxygen

src/lib.rs

@@ -377,8 +377,9 @@ impl GPTHeader {
 }
 
 /// A wrapper type for `String` that represents a partition's name.
+/// Also stores a copy of raw bytes in the partition name field.
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub struct PartitionName(String);
+pub struct PartitionName(String, [u8; 72]);
 
 impl PartitionName {
     /// Extracts a string slice containing the entire `PartitionName`.
@@ -395,7 +396,13 @@ impl std::fmt::Display for PartitionName {
 
 impl From<&str> for PartitionName {
     fn from(value: &str) -> PartitionName {
-        PartitionName(value.to_string())
+        // Convert to UTF-16 LE and store in the raw buffer
+        let utf16_converted = value.encode_utf16();
+        let mut raw_buf = [0; 72];
+        for (idx, chr) in utf16_converted.into_iter().take(36).enumerate() {
+            raw_buf[idx * 2..=idx * 2 + 1].copy_from_slice(&chr.to_le_bytes());
+        }
+        PartitionName(value.to_string(), raw_buf)
     }
 }
 
@@ -412,18 +419,25 @@ impl<'de> Visitor<'de> for UTF16LEVisitor {
     where
         A: SeqAccess<'de>,
     {
-        let mut v = Vec::new();
+        let mut v: Vec<u16> = Vec::new();
+        let mut raw_buf = [0; 72];
         let mut end = false;
-        loop {
-            match seq.next_element()? {
-                Some(0) => end = true,
-                Some(x) if !end => v.push(x),
-                Some(_) => {}
-                None => break,
+        let mut idx = 0;
+        while let Some(x) = seq.next_element()? {
+            if idx >= 72 {
+                break;
+            }
+            if x == 0 {
+                end = true;
+            }
+            if !end {
+                v.push(x);
             }
-        }
 
-        Ok(PartitionName(String::from_utf16_lossy(&v)))
+            raw_buf[idx..=idx + 1].copy_from_slice(&x.to_le_bytes());
+            idx += 2;
+        }
+        Ok(PartitionName(String::from_utf16_lossy(&v), raw_buf))
     }
 }
 
@@ -441,9 +455,9 @@ impl Serialize for PartitionName {
     where
         S: Serializer,
     {
-        let s = self.0.encode_utf16();
-        let mut seq = serializer.serialize_tuple(36)?;
-        for x in s.chain([0].iter().cycle().cloned()).take(36) {
+        // Use the content in the raw buffer.
+        let mut seq = serializer.serialize_tuple(72)?;
+        for x in self.1.into_iter().take(72) {
             seq.serialize_element(&x)?;
         }
         seq.end()