tar/export: Fix error with zero-sized hardlinked files

In the case where we already emitted an object into the tar stream,
we wouldn't previously set the file type and size into the tar
header structure that we passed into the hardlink emission function.
This would cause an error when accessing the (logically) uninitialized `size()`.

Fix the writer function to always set the file type and size unconditionally,
and also rework the consumer side to make the logic even clearer.

Signed-off-by: Colin Walters <[email protected]>

Author: cgwalters

ostree-ext/src/tar/export.rs

@@ -430,7 +430,11 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
         let mode = meta.attribute_uint32("unix::mode");
         h.set_mode(self.filter_mode(mode));
         if instream.is_some() {
+            h.set_entry_type(tar::EntryType::Regular);
             h.set_size(meta.size() as u64);
+        } else {
+            h.set_entry_type(tar::EntryType::Symlink);
+            h.set_size(0);
         }
         if !self.wrote_content.contains(checksum) {
             let inserted = self.wrote_content.insert(checksum.to_string());
@@ -445,8 +449,6 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
             if let Some(instream) = instream {
                 ensure!(meta.file_type() == gio::FileType::Regular);
 
-                h.set_entry_type(tar::EntryType::Regular);
-                h.set_size(meta.size() as u64);
                 let mut instream = BufReader::with_capacity(BUF_CAPACITY, instream.into_read());
                 self.out
                     .append_data(&mut h, &path, &mut instream)
@@ -461,8 +463,6 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
                     .to_str()
                     .ok_or_else(|| anyhow!("Invalid UTF-8 symlink target: {target:?}"))?;
                 let context = || format!("Writing content symlink: {}", checksum);
-                h.set_entry_type(tar::EntryType::Symlink);
-                h.set_size(0);
                 // Handle //chkconfig, see above
                 if symlink_is_denormal(target) {
                     h.set_link_name_literal(target).with_context(context)?;
@@ -501,15 +501,20 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
         mut h: tar::Header,
         dest: &Utf8Path,
     ) -> Result<()> {
-        // Query the original size first
-        let size = h.size().context("Querying size for hardlink append")?;
         // Don't create hardlinks to zero-sized files, it's much more likely
         // to result in generated tar streams from container builds resulting
         // in a modified linked-to file in /sysroot, which we don't currently handle.
         // And in the case where the input is *not* zero sized, we still output
         // a hardlink of size zero, as this is what is normal.
+        let is_regular_zerosized = if h.entry_type() == tar::EntryType::Regular {
+            let size = h.size().context("Querying size for hardlink append")?;
+            size == 0
+        } else {
+            false
+        };
+        // Link sizes shoud always be zero
         h.set_size(0);
-        if h.entry_type() == tar::EntryType::Regular && size == 0 {
+        if is_regular_zerosized {
             self.out.append_data(&mut h, dest, &mut std::io::empty())?;
         } else {
             h.set_entry_type(tar::EntryType::Link);