Make to_u32 safe and sound

tafia · Feb 1, 2021 · 8ff7218 · 8ff7218
1 parent e88c6ff
commit 8ff7218
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Showing 2 changed files with 11 additions and 9 deletions.
diff --git a/src/cfb.rs b/src/cfb.rs
@@ -83,15 +83,15 @@ impl Cfb {
         debug!("load difat");
         let mut sector_id = h.difat_start;
         while sector_id < RESERVED_SECTORS {
-            difat.extend_from_slice(to_u32(sectors.get(sector_id, reader)?));
+            difat.extend(to_u32(sectors.get(sector_id, reader)?));
             sector_id = difat.pop().unwrap(); //TODO: check if in infinite loop
         }
 
         // load the FATs
         debug!("load fat");
         let mut fats = Vec::with_capacity(h.fat_len);
         for id in difat.into_iter().filter(|id| *id != FREESECT) {
-            fats.extend_from_slice(to_u32(sectors.get(id, reader)?));
+            fats.extend(to_u32(sectors.get(id, reader)?));
         }
 
         // get the list of directory sectors
@@ -116,7 +116,7 @@ impl Cfb {
             reader,
             h.mini_fat_len * h.sector_size,
         )?;
-        let minifat = to_u32(&minifat).to_vec();
+        let minifat = to_u32(&minifat).collect();
         Ok(Cfb {
             directories: dirs,
             sectors,
@@ -208,7 +208,7 @@ impl Header {
         let difat_len = read_usize(&buf[62..76]);
 
         let mut difat = Vec::with_capacity(difat_len);
-        difat.extend_from_slice(to_u32(&buf[76..512]));
+        difat.extend(to_u32(&buf[76..512]));
 
         Ok((
             Header {

diff --git a/src/utils.rs b/src/utils.rs
@@ -12,11 +12,13 @@ macro_rules! from_err {
     };
 }
 
-/// Converts a &[u8] into a &[u32]
-pub fn to_u32(s: &[u8]) -> &[u32] {
+/// Converts a &[u8] into an iterator of `u32`s
+pub fn to_u32(s: &[u8]) -> impl ExactSizeIterator<Item = u32> + '_ {
     assert_eq!(s.len() % 4, 0);
-    unsafe { std::slice::from_raw_parts(s as *const [u8] as *const u32, s.len() / 4) }
+    s.chunks(4)
+        .map(|data| u32::from_ne_bytes([data[0], data[1], data[2], data[3]]))
 }
+
 pub fn read_slice<T>(s: &[u8]) -> T {
     unsafe { std::ptr::read(&s[..std::mem::size_of::<T>()] as *const [u8] as *const T) }
 }
@@ -1039,8 +1041,8 @@ mod tests {
     fn sound_to_u32() {
         let data = b"ABCDEFGH";
         assert_eq!(
-            to_u32(data),
-            &[u32::from_ne_bytes(*b"ABCD"), u32::from_ne_bytes(*b"EFGH")]
+            to_u32(data).collect::<Vec<_>>(),
+            [u32::from_ne_bytes(*b"ABCD"), u32::from_ne_bytes(*b"EFGH")]
         );
     }