securityfs: add the ability to support symlinks

Signed-off-by: John Johansen <john.johansen@canonical.com>
Reviewed-by: Seth Arnold <seth.arnold@canonical.com>
Acked-by: Kees Cook <keescook@chromium.org>

include/linux/security.h

@@ -1651,6 +1651,10 @@ extern struct dentry *securityfs_create_file(const char *name, umode_t mode,
 					     struct dentry *parent, void *data,
 					     const struct file_operations *fops);
 extern struct dentry *securityfs_create_dir(const char *name, struct dentry *parent);
+struct dentry *securityfs_create_symlink(const char *name,
+					 struct dentry *parent,
+					 const char *target,
+					 const struct inode_operations *iops);
 extern void securityfs_remove(struct dentry *dentry);
 
 #else /* CONFIG_SECURITYFS */
@@ -1670,6 +1674,14 @@ static inline struct dentry *securityfs_create_file(const char *name,
 	return ERR_PTR(-ENODEV);
 }
 
+static inline struct dentry *securityfs_create_symlink(const char *name,
+					struct dentry *parent,
+					const char *target,
+					const struct inode_operations *iops)
+{
+	return ERR_PTR(-ENODEV);
+}
+
 static inline void securityfs_remove(struct dentry *dentry)
 {}
 

security/inode.c

@@ -26,11 +26,31 @@
 static struct vfsmount *mount;
 static int mount_count;
 
+static void securityfs_evict_inode(struct inode *inode)
+{
+	truncate_inode_pages_final(&inode->i_data);
+	clear_inode(inode);
+	if (S_ISLNK(inode->i_mode))
+		kfree(inode->i_link);
+}
+
+static const struct super_operations securityfs_super_operations = {
+	.statfs		= simple_statfs,
+	.evict_inode	= securityfs_evict_inode,
+};
+
 static int fill_super(struct super_block *sb, void *data, int silent)
 {
 	static const struct tree_descr files[] = {{""}};
+	int error;
+
+	error = simple_fill_super(sb, SECURITYFS_MAGIC, files);
+	if (error)
+		return error;
+
+	sb->s_op = &securityfs_super_operations;
 
-	return simple_fill_super(sb, SECURITYFS_MAGIC, files);
+	return 0;
 }
 
 static struct dentry *get_sb(struct file_system_type *fs_type,
@@ -48,7 +68,7 @@ static struct file_system_type fs_type = {
 };
 
 /**
- * securityfs_create_file - create a file in the securityfs filesystem
+ * securityfs_create_dentry - create a dentry in the securityfs filesystem
  *
  * @name: a pointer to a string containing the name of the file to create.
  * @mode: the permission that the file should have
@@ -60,34 +80,35 @@ static struct file_system_type fs_type = {
  *        the open() call.
  * @fops: a pointer to a struct file_operations that should be used for
  *        this file.
+ * @iops: a point to a struct of inode_operations that should be used for
+ *        this file/dir
  *
- * This is the basic "create a file" function for securityfs.  It allows for a
- * wide range of flexibility in creating a file, or a directory (if you
- * want to create a directory, the securityfs_create_dir() function is
- * recommended to be used instead).
+ * This is the basic "create a file/dir/symlink" function for
+ * securityfs.  It allows for a wide range of flexibility in creating
+ * a file, or a directory (if you want to create a directory, the
+ * securityfs_create_dir() function is recommended to be used
+ * instead).
  *
  * This function returns a pointer to a dentry if it succeeds.  This
- * pointer must be passed to the securityfs_remove() function when the file is
- * to be removed (no automatic cleanup happens if your module is unloaded,
- * you are responsible here).  If an error occurs, the function will return
- * the error value (via ERR_PTR).
+ * pointer must be passed to the securityfs_remove() function when the
+ * file is to be removed (no automatic cleanup happens if your module
+ * is unloaded, you are responsible here).  If an error occurs, the
+ * function will return the error value (via ERR_PTR).
  *
  * If securityfs is not enabled in the kernel, the value %-ENODEV is
  * returned.
  */
-struct dentry *securityfs_create_file(const char *name, umode_t mode,
-				   struct dentry *parent, void *data,
-				   const struct file_operations *fops)
+static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
+					struct dentry *parent, void *data,
+					const struct file_operations *fops,
+					const struct inode_operations *iops)
 {
 	struct dentry *dentry;
-	int is_dir = S_ISDIR(mode);
 	struct inode *dir, *inode;
 	int error;
 
-	if (!is_dir) {
-		BUG_ON(!fops);
+	if (!(mode & S_IFMT))
 		mode = (mode & S_IALLUGO) | S_IFREG;
-	}
 
 	pr_debug("securityfs: creating file '%s'\n",name);
 
@@ -120,11 +141,14 @@ struct dentry *securityfs_create_file(const char *name, umode_t mode,
 	inode->i_mode = mode;
 	inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
 	inode->i_private = data;
-	if (is_dir) {
+	if (S_ISDIR(mode)) {
 		inode->i_op = &simple_dir_inode_operations;
 		inode->i_fop = &simple_dir_operations;
 		inc_nlink(inode);
 		inc_nlink(dir);
+	} else if (S_ISLNK(mode)) {
+		inode->i_op = iops ? iops : &simple_symlink_inode_operations;
+		inode->i_link = data;
 	} else {
 		inode->i_fop = fops;
 	}
@@ -141,6 +165,38 @@ struct dentry *securityfs_create_file(const char *name, umode_t mode,
 	simple_release_fs(&mount, &mount_count);
 	return dentry;
 }
+
+/**
+ * securityfs_create_file - create a file in the securityfs filesystem
+ *
+ * @name: a pointer to a string containing the name of the file to create.
+ * @mode: the permission that the file should have
+ * @parent: a pointer to the parent dentry for this file.  This should be a
+ *          directory dentry if set.  If this parameter is %NULL, then the
+ *          file will be created in the root of the securityfs filesystem.
+ * @data: a pointer to something that the caller will want to get to later
+ *        on.  The inode.i_private pointer will point to this value on
+ *        the open() call.
+ * @fops: a pointer to a struct file_operations that should be used for
+ *        this file.
+ *
+ * This function creates a file in securityfs with the given @name.
+ *
+ * This function returns a pointer to a dentry if it succeeds.  This
+ * pointer must be passed to the securityfs_remove() function when the file is
+ * to be removed (no automatic cleanup happens if your module is unloaded,
+ * you are responsible here).  If an error occurs, the function will return
+ * the error value (via ERR_PTR).
+ *
+ * If securityfs is not enabled in the kernel, the value %-ENODEV is
+ * returned.
+ */
+struct dentry *securityfs_create_file(const char *name, umode_t mode,
+				      struct dentry *parent, void *data,
+				      const struct file_operations *fops)
+{
+	return securityfs_create_dentry(name, mode, parent, data, fops, NULL);
+}
 EXPORT_SYMBOL_GPL(securityfs_create_file);
 
 /**
@@ -165,12 +221,58 @@ EXPORT_SYMBOL_GPL(securityfs_create_file);
  */
 struct dentry *securityfs_create_dir(const char *name, struct dentry *parent)
 {
-	return securityfs_create_file(name,
-				      S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO,
-				      parent, NULL, NULL);
+	return securityfs_create_file(name, S_IFDIR | 0755, parent, NULL, NULL);
 }
 EXPORT_SYMBOL_GPL(securityfs_create_dir);
 
+/**
+ * securityfs_create_symlink - create a symlink in the securityfs filesystem
+ *
+ * @name: a pointer to a string containing the name of the symlink to
+ *        create.
+ * @parent: a pointer to the parent dentry for the symlink.  This should be a
+ *          directory dentry if set.  If this parameter is %NULL, then the
+ *          directory will be created in the root of the securityfs filesystem.
+ * @target: a pointer to a string containing the name of the symlink's target.
+ *          If this parameter is %NULL, then the @iops parameter needs to be
+ *          setup to handle .readlink and .get_link inode_operations.
+ * @iops: a pointer to the struct inode_operations to use for the symlink. If
+ *        this parameter is %NULL, then the default simple_symlink_inode
+ *        operations will be used.
+ *
+ * This function creates a symlink in securityfs with the given @name.
+ *
+ * This function returns a pointer to a dentry if it succeeds.  This
+ * pointer must be passed to the securityfs_remove() function when the file is
+ * to be removed (no automatic cleanup happens if your module is unloaded,
+ * you are responsible here).  If an error occurs, the function will return
+ * the error value (via ERR_PTR).
+ *
+ * If securityfs is not enabled in the kernel, the value %-ENODEV is
+ * returned.
+ */
+struct dentry *securityfs_create_symlink(const char *name,
+					 struct dentry *parent,
+					 const char *target,
+					 const struct inode_operations *iops)
+{
+	struct dentry *dent;
+	char *link = NULL;
+
+	if (target) {
+		link = kstrdup(target, GFP_KERNEL);
+		if (!link)
+			return ERR_PTR(-ENOMEM);
+	}
+	dent = securityfs_create_dentry(name, S_IFLNK | 0444, parent,
+					link, NULL, iops);
+	if (IS_ERR(dent))
+		kfree(link);
+
+	return dent;
+}
+EXPORT_SYMBOL_GPL(securityfs_create_symlink);
+
 /**
  * securityfs_remove - removes a file or directory from the securityfs filesystem
  *