Prevent writing through a symlink to arbitrary files

src/entry.rs

@@ -482,7 +482,16 @@ impl<'a> EntryFields<'a> {
         // As a result if we don't recognize the kind we just write out the file
         // as we would normally.
 
-        fs::File::create(dst).and_then(|mut f| {
+        // Remove an existing file, if any, to avoid writing through
+        // symlinks/hardlinks to weird locations. The tar archive says this is a
+        // regular file, so let's make it a regular file.
+        (|| -> io::Result<()> {
+            match fs::remove_file(dst) {
+                Ok(()) => {}
+                Err(ref e) if e.kind() == io::ErrorKind::NotFound => {}
+                Err(e) => return Err(e)
+            }
+            let mut f = fs::File::create(dst)?;
             for io in self.data.drain(..) {
                 match io {
                     EntryIo::Data(mut d) => {
@@ -500,7 +509,7 @@ impl<'a> EntryFields<'a> {
                 }
             }
             Ok(())
-        }).map_err(|e| {
+        })().map_err(|e| {
             let header = self.header.path_bytes();
             TarError::new(&format!("failed to unpack `{}` into `{}`",
                                    String::from_utf8_lossy(&header),

tests/entry.rs

@@ -283,3 +283,38 @@ fn modify_hard_link_just_created() {
     t!(t!(File::open(&test)).read_to_end(&mut contents));
     assert_eq!(contents.len(), 0);
 }
+
+#[test]
+fn modify_symlink_just_created() {
+    let mut ar = tar::Builder::new(Vec::new());
+
+    let mut header = tar::Header::new_gnu();
+    header.set_size(0);
+    header.set_entry_type(tar::EntryType::Symlink);
+    t!(header.set_path("foo"));
+    t!(header.set_link_name("../test"));
+    header.set_cksum();
+    t!(ar.append(&header, &[][..]));
+
+    let mut header = tar::Header::new_gnu();
+    header.set_size(1);
+    header.set_entry_type(tar::EntryType::Regular);
+    t!(header.set_path("foo"));
+    header.set_cksum();
+    t!(ar.append(&header, &b"x"[..]));
+
+    let bytes = t!(ar.into_inner());
+    let mut ar = tar::Archive::new(&bytes[..]);
+
+    let td = t!(TempDir::new("tar"));
+
+    let test = td.path().join("test");
+    t!(File::create(&test));
+
+    let dir = td.path().join("dir");
+    t!(ar.unpack(&dir));
+
+    let mut contents = Vec::new();
+    t!(t!(File::open(&test)).read_to_end(&mut contents));
+    assert_eq!(contents.len(), 0);
+}