Merge pull request #125 from ossobv/wjd-refuse_descent_into_own_mountpoint

Perform checks to ensure that we're not descending into ourself.

encfs/DirNode.cpp

@@ -254,13 +254,9 @@ DirNode::DirNode(EncFS_Context *_ctx, const string &sourceDir,
   Lock _lock(mutex);
 
   ctx = _ctx;
-  rootDir = sourceDir;
+  rootDir = sourceDir; // .. and fsConfig->opts->mountPoint have trailing slash
   fsConfig = _config;
 
-  // make sure rootDir ends in '/', so that we can form a path by appending
-  // the rest..
-  if (rootDir[rootDir.length() - 1] != '/') rootDir.append(1, '/');
-
   naming = fsConfig->nameCoding;
 }
 
@@ -277,6 +273,27 @@ string DirNode::rootDirectory() {
   return string(rootDir, 0, rootDir.length() - 1);
 }
 
+bool DirNode::touchesMountpoint( const char *realPath ) const {
+  const string &mountPoint = fsConfig->opts->mountPoint;
+  // compare mountPoint up to the leading slash.
+  // examples:
+  //   mountPoint      = /home/user/Junk/experiment/
+  //   realPath        = /home/user/Junk/experiment
+  //   realPath        = /home/user/Junk/experiment/abc
+  const ssize_t len = mountPoint.length() - 1;
+
+  if (mountPoint.compare(0, len, realPath, len) == 0) {
+    // if next character is a NUL or a slash, then we're referencing our
+    // mount point:
+    //   .../experiment => true
+    //   .../experiment/... => true
+    //   .../experiment2/abc => false
+    return realPath[len] == '\0' || realPath[len] == '/';
+  }
+
+  return false;
+}
+
 /**
  * Encrypt a plain-text file path to the ciphertext path with the
  * ciphertext root directory name prefixed.

encfs/DirNode.h

@@ -86,6 +86,9 @@ class DirNode {
   // return the path to the root directory
   std::string rootDirectory();
 
+  // recursive lookup check
+  bool touchesMountpoint(const char *realPath) const;
+
   // find files
   shared_ptr<FileNode> lookupNode(const char *plaintextName,
                                   const char *requestor);

encfs/FileUtils.h

@@ -69,6 +69,7 @@ enum ConfigMode { Config_Prompt, Config_Standard, Config_Paranoia };
  */
 struct EncFS_Opts {
   std::string rootDir;
+  std::string mountPoint; // where to make filesystem visible
   bool createIfNotFound;  // create filesystem if not found
   bool idleTracking;      // turn on idle monitoring of filesystem
   bool mountOnDemand;     // mounting on-demand

encfs/encfs.cpp

@@ -139,6 +139,14 @@ static int withFileNode(const char *opName, const char *path,
 
     rAssert(fnode.get() != NULL);
     rLog(Info, "%s %s", opName, fnode->cipherName());
+
+    // check that we're not recursing into the mount point itself
+    if (FSRoot->touchesMountpoint(fnode->cipherName())) {
+      rInfo("%s error: Tried to touch mountpoint: '%s'",
+            opName, fnode->cipherName());
+      return res; // still -EIO
+    }
+
     res = op(fnode.get());
 
     if (res < 0) rInfo("%s error: %s", opName, strerror(-res));

encfs/main.cpp

@@ -74,7 +74,6 @@ const int MaxFuseArgs = 32;
  * derived from the arguments
  */
 struct EncFS_Args {
-  string mountPoint;  // where to make filesystem visible
   bool isDaemon;      // true == spawn in background, log to syslog
   bool isThreaded;    // true == threaded
   bool isVerbose;     // false == only enable warning/error messages
@@ -373,8 +372,10 @@ static bool processArgs(int argc, char *argv[],
   // we should have at least 2 arguments left over - the source directory and
   // the mount point.
   if (optind + 2 <= argc) {
+    // both rootDir and mountPoint are assumed to be slash terminated in the
+    // rest of the code.
     out->opts->rootDir = slashTerminate(argv[optind++]);
-    out->mountPoint = argv[optind++];
+    out->opts->mountPoint = slashTerminate(argv[optind++]);
   } else {
     // no mount point specified
     rWarning(_("Missing one or more arguments, aborting."));
@@ -420,7 +421,7 @@ static bool processArgs(int argc, char *argv[],
   }
 
   // sanity check
-  if (out->isDaemon && (!isAbsolutePath(out->mountPoint.c_str()) ||
+  if (out->isDaemon && (!isAbsolutePath(out->opts->mountPoint.c_str()) ||
                         !isAbsolutePath(out->opts->rootDir.c_str()))) {
     cerr <<
         // xgroup(usage)
@@ -431,7 +432,7 @@ static bool processArgs(int argc, char *argv[],
 
   // the raw directory may not be a subdirectory of the mount point.
   {
-    string testMountPoint = slashTerminate(out->mountPoint);
+    string testMountPoint = out->opts->mountPoint;
     string testRootDir = out->opts->rootDir.substr(0, testMountPoint.length());
 
     if (testMountPoint == testRootDir) {
@@ -464,15 +465,15 @@ static bool processArgs(int argc, char *argv[],
     rWarning(_("Unable to locate root directory, aborting."));
     return false;
   }
-  if (!isDirectory(out->mountPoint.c_str()) &&
-      !userAllowMkdir(out->opts->annotate ? 2 : 0, out->mountPoint.c_str(),
+  if (!isDirectory(out->opts->mountPoint.c_str()) &&
+      !userAllowMkdir(out->opts->annotate ? 2 : 0, out->opts->mountPoint.c_str(),
                       0700)) {
     rWarning(_("Unable to locate mount point, aborting."));
     return false;
   }
 
   // fill in mount path for fuse
-  out->fuseArgv[1] = out->mountPoint.c_str();
+  out->fuseArgv[1] = out->opts->mountPoint.c_str();
 
   return true;
 }
@@ -767,7 +768,7 @@ static bool unmountFS(EncFS_Context *ctx) {
   shared_ptr<EncFS_Args> arg = ctx->args;
   if (arg->opts->mountOnDemand) {
     rDebug("Detaching filesystem %s due to inactivity",
-           arg->mountPoint.c_str());
+           arg->opts->mountPoint.c_str());
 
     ctx->setRoot(shared_ptr<DirNode>());
     return false;
@@ -775,8 +776,8 @@ static bool unmountFS(EncFS_Context *ctx) {
     // Time to unmount!
     // xgroup(diag)
     rWarning(_("Unmounting filesystem %s due to inactivity"),
-             arg->mountPoint.c_str());
-    fuse_unmount(arg->mountPoint.c_str());
+             arg->opts->mountPoint.c_str());
+    fuse_unmount(arg->opts->mountPoint.c_str());
     return true;
   }
 }