TSCBasic: correct a use-after-free on Windows (swiftlang#232)

This corrects a use-after-free caused by a pointer escape. The lifetime of the pointer is not guaranteed, and the OS may free the pointer early, particularly with OSSA. Push the handling into the closure to ensure that the lifetime is extended for the duration.
CodaFi · Jun 28, 2021 · c5dd301 · c5dd301
1 parent 4c4ad66
commit c5dd301
Showing 1 changed file with 7 additions and 6 deletions.
diff --git a/Sources/TSCBasic/Path.swift b/Sources/TSCBasic/Path.swift
@@ -730,13 +730,14 @@ private struct UNIXPath: Path {
 
     func suffix(withDot: Bool) -> String? {
 #if os(Windows)
-        let ext = self.string.withCString(encodedAs: UTF16.self) {
-            PathFindExtensionW($0)
+        return self.string.withCString(encodedAs: UTF16.self) {
+          if let pointer = PathFindExtensionW($0) {
+            let substring = String(decodingCString: pointer, as: UTF16.self)
+            guard substring.length > 0 else { return nil }
+            return withDot ? substring : String(substring.dropFirst(1))
+          }
+          return nil
         }
-        var result = String(decodingCString: ext!, as: UTF16.self)
-        guard result.length > 0 else { return nil }
-        if !withDot { result.removeFirst(1) }
-        return result
 #else
         // FIXME: This method seems too complicated; it should be simplified,
         //        if possible, and certainly optimized (using UTF8View).