dart:io | Ensure that Directory.list terminates even when symbolic links create loops in the file s…

runtime/bin/directory_linux.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_LINUX)
 
 #include "bin/directory.h"
 
 #include <dirent.h>  // NOLINT
@@ skipping 36 matching lines @@
     }
   }
 
   void Reset(int new_length) {
     length = new_length;
     data[length] = '\0';
   }
 };
 
 
+// A linked list of symbolic links, with their unique file system identifiers.
+// These are scanned to detect loops while doing a recursive directory listing.
+struct LinkList {
+  dev_t dev;
+  ino_t ino;
+  LinkList* next;
+};
+
+
 // Forward declarations.
 static bool ListRecursively(PathBuffer* path,
                             bool recursive,
                             bool follow_links,
+                            LinkList* seen,
                             DirectoryListing* listing);
 static bool DeleteRecursively(PathBuffer* path);
 
 
 static void PostError(DirectoryListing *listing,
                       const char* dir_name) {
   listing->HandleError(dir_name);
 }
 
 
 static bool HandleDir(char* dir_name,
                       PathBuffer* path,
                       bool recursive,
                       bool follow_links,
+                      LinkList* seen,
                       DirectoryListing *listing) {
   if (strcmp(dir_name, ".") == 0) return true;
   if (strcmp(dir_name, "..") == 0) return true;
   if (!path->Add(dir_name)) {
     PostError(listing, path->data);
     return false;
   }
   return listing->HandleDirectory(path->data) &&
-      (!recursive || ListRecursively(path, recursive, follow_links, listing));
+      (!recursive ||
+       ListRecursively(path, recursive, follow_links, seen, listing));
 }
 
 
 static bool HandleFile(char* file_name,
                        PathBuffer* path,
                        DirectoryListing *listing) {
   if (!path->Add(file_name)) {
     PostError(listing, path->data);
     return false;
   }
   return listing->HandleFile(path->data);
 }
 
 
 static bool HandleLink(char* link_name,
                        PathBuffer* path,
                        DirectoryListing *listing) {
   if (!path->Add(link_name)) {
     PostError(listing, path->data);
     return false;
   }
   return listing->HandleLink(path->data);
 }
 
 
 static bool ListRecursively(PathBuffer* path,
                             bool recursive,
                             bool follow_links,
+                            LinkList* seen,
                             DirectoryListing *listing) {
   if (!path->Add(File::PathSeparator())) {
     PostError(listing, path->data);
     return false;
   }
   DIR* dir_pointer;
   do {
     dir_pointer = opendir(path->data);
   } while (dir_pointer == NULL && errno == EINTR);
   if (dir_pointer == NULL) {
@@ skipping 11 matching lines @@
   while ((status = TEMP_FAILURE_RETRY(readdir_r(dir_pointer,
                                                 &entry,
                                                 &result))) == 0 &&
          result != NULL) {
     switch (entry.d_type) {
       case DT_DIR:
         success = HandleDir(entry.d_name,
                             path,
                             recursive,
                             follow_links,
+                            seen,
                             listing) && success;
         break;
       case DT_REG:
         success = HandleFile(entry.d_name,
                              path,
                              listing) && success;
         break;
       case DT_LNK:
         if (!follow_links) {
           success = HandleLink(entry.d_name,
                                path,
                                listing) && success;
           break;
         }
         // Else fall through to next case.
         // Fall through.
       case DT_UNKNOWN: {
         // On some file systems the entry type is not determined by
         // readdir_r. For those and for links we use stat to determine
         // the actual entry type. Notice that stat returns the type of
         // the file pointed to.
         struct stat entry_info;
         if (!path->Add(entry.d_name)) {
           success = false;
           break;
         }
         int stat_success;
-        if (follow_links) {
-          stat_success = TEMP_FAILURE_RETRY(stat(path->data, &entry_info));
-          if (stat_success == -1) {
-            stat_success = TEMP_FAILURE_RETRY(lstat(path->data, &entry_info));
-          }
-        } else {
-          stat_success = TEMP_FAILURE_RETRY(lstat(path->data, &entry_info));
-        }
+        stat_success = TEMP_FAILURE_RETRY(lstat(path->data, &entry_info));
         if (stat_success == -1) {
           success = false;
           PostError(listing, path->data);
           break;
         }
+        if (follow_links && S_ISLNK(entry_info.st_mode)) {
+          // Check to see if we are in a loop created by a symbolic link.
+          LinkList current_link = { entry_info.st_dev,
+                                    entry_info.st_ino,
+                                    seen };
+          LinkList* previous = seen;
+          bool looping_link = false;
+          while (previous != NULL) {
+            if (previous->dev == current_link.dev &&
+                previous->ino == current_link.ino) {

[Søren Gjesse, 2013/04/10 11:33:23]

How about adding a compare method (or operator==) to LinkList?

[Bill Hesse, 2013/04/10 12:49:47]

I would do that if we had another use.  But that turns it from a struct to a
class (I don't think the style guide allows adding methods to structs).  It is
also a weird == that ignores the next field.  So how about no.

+              // Report the looping link as a link, rather than following it.
+              path->Reset(path_length);
+              success = HandleLink(entry.d_name,
+                                   path,
+                                   listing) && success;
+              looping_link = true;
+              break;
+            }
+            previous = previous->next;
+          }
+          if (looping_link) break;
+          stat_success = TEMP_FAILURE_RETRY(stat(path->data, &entry_info));
+          if (stat_success == -1) {
+            // Report a broken link as a link, even if follow_links is true.
+            path->Reset(path_length);
+            success = HandleLink(entry.d_name,
+                                 path,
+                                 listing) && success;
+            break;
+          }
+          if (S_ISDIR(entry_info.st_mode)) {
+            // Recurse into the subdirectory with current_link added to the
+            // linked list of seen file system links.
+            path->Reset(path_length);
+            success = HandleDir(entry.d_name,
+                                path,
+                                recursive,
+                                follow_links,
+                                &current_link,
+                                listing) && success;
+            break;
+          }
+        }
         path->Reset(path_length);
         if (S_ISDIR(entry_info.st_mode)) {
           success = HandleDir(entry.d_name,
                               path,
                               recursive,
                               follow_links,
+                              seen,
                               listing) && success;
         } else if (S_ISREG(entry_info.st_mode)) {
           success = HandleFile(entry.d_name,
                                path,
                                listing) && success;
         } else if (S_ISLNK(entry_info.st_mode)) {
           success = HandleLink(entry.d_name,
                                path,
                                listing) && success;
         }
@@ skipping 121 matching lines @@
 
 bool Directory::List(const char* dir_name,
                      bool recursive,
                      bool follow_links,
                      DirectoryListing *listing) {
   PathBuffer path;
   if (!path.Add(dir_name)) {
     PostError(listing, dir_name);
     return false;
   }
-  return ListRecursively(&path, recursive, follow_links, listing);
+  return ListRecursively(&path, recursive, follow_links, NULL, listing);
 }
 
 
 Directory::ExistsResult Directory::Exists(const char* dir_name) {
   struct stat entry_info;
   int success = TEMP_FAILURE_RETRY(stat(dir_name, &entry_info));
   if (success == 0) {
     if (S_ISDIR(entry_info.st_mode)) {
       return EXISTS;
     } else {
@@ skipping 84 matching lines @@
 }
 
 
 bool Directory::Rename(const char* path, const char* new_path) {
   ExistsResult exists = Exists(path);
   if (exists != EXISTS) return false;
   return (TEMP_FAILURE_RETRY(rename(path, new_path)) == 0);
 }
 
 #endif  // defined(TARGET_OS_LINUX)