Revert "[XPCOM] Deal with lstat potentially lying in nsLocalFileUnix."

This reverts commit c127f58ef3.

toolkit/mozapps/extensions/internal/AddonUpdateChecker.jsm

@@ -613,14 +613,6 @@ function UpdateParser(aId, aUpdateKey, aUrl, aObserver) {
   let requireBuiltIn = Services.prefs.getBoolPref(PREF_UPDATE_REQUIREBUILTINCERTS, true);
 
   logger.debug("Requesting " + aUrl);
-
-  if (!aUrl) {
-    logger.warn("Request failed: empty update manifest URL");
-    this._doneAt = new Error("UP_emptyManifestURL");
-    this.notifyError(AddonUpdateChecker.ERROR_DOWNLOAD_ERROR);
-    return;
-  }
-
   try {
     this.request = new ServiceRequest();
     this.request.open("GET", this.url, true);

xpcom/io/nsLocalFileUnix.cpp

@@ -1720,14 +1720,11 @@ nsLocalFile::GetNativeTarget(nsACString& aResult)
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
-  ssize_t written = readlink(mPath.get(), target.BeginWriting(), size_t(size));
-  if (written < 0) {
+  if (readlink(mPath.get(), target, (size_t)size) < 0) {
     free(target);
     return NSRESULT_FOR_ERRNO();
   }
-  // Target might have changed since the lstat call, or lstat might lie, see bug
-  // 1791029.
-  target.Truncate(written);
+  target[size] = '\0';
 
   nsresult rv = NS_OK;
   nsCOMPtr<nsIFile> self(this);
@@ -1778,15 +1775,12 @@ nsLocalFile::GetNativeTarget(nsACString& aResult)
       size = newSize;
     }
 
-    ssize_t linkLen = readlink(flatRetval.get(), target, size);
+    int32_t linkLen = readlink(flatRetval.get(), target, size);
     if (linkLen == -1) {
       rv = NSRESULT_FOR_ERRNO();
       break;
     }
-    // Target might have changed since the lstat call, or lstat might lie, see bug
-    // 1791029.
-    newTarget.Truncate(linkLen);
-    target = newTarget;
+    target[linkLen] = '\0';
   }
 
   free(target);