File Access Example - Using P.I.P.S.

This example application shows, using a P.I.P.S. (P.I.P.S. Is POSIX on Symbian OS) program, the restrictions on file access that are imposed by the Symbian OS Platform Security model.

It shows that programs can access their own directories, but cannot, without platform security capabilities not available to ordinary programs, access the directories of other programs, or the system binary directory sys/bin.

This example defines an executable file with no platform security capabilities. The program first creates its own secure directory that it can write to and read from. It then attempts to use a file in a private directory of another program, and then in sys/bin, and shows that these attempts are denied.

This example is located in examples\PIPS\FileAccessExample.

The following sections provide more information about the steps that the example performs.

The example creates an empty secure directory for the program by using the mkdir() function.

This empty secure directory is created in C:\private\E80000C9, as 0xE80000C9 is a unique identifier for the program (as specified by the third UID in its project file).

The example writes and reads a file in the secure directory using the fopen() and other file stream functions.

The example attempts to write and read a file in the secure directory of another program.

The fopen() function is expected to return NULL, indicating that access is not possible, as the program has insufficient platform security capabilities.

The example attempts to write and read a file in the system's sys/bin directory, where program binaries are stored.

Again, the fopen() function is expected to return NULL, indicating that access is not possible, as the program has insufficient platform security capabilities.

The Symbian OS build process describes how to build this example application.

The example builds an executable called fileaccessexample.exe in the standard locations.

To run the example, start fileaccessexample.exe from the file system or from your IDE. After launching the executable, depending on the emulator you are using, you may need to navigate away from the application launcher or shell screen to view the console.

// bld.inf
// Component description file
//
// Copyright (c) 2007 Symbian Ltd.  All rights reserved.

PRJ_MMPFILES
fileaccessexample.mmp

// fileaccessexample.mmp
//
// Copyright (C) Symbian Software Ltd 2007.  All rights reserved.

TARGET fileaccessexample.exe
TARGETTYPE exe

UID  0x1000008D 0xE80000C9
CAPABILITY NONE

SOURCEPATH    .
SOURCE fileaccessexample.c

SYSTEMINCLUDE   \epoc32\include
SYSTEMINCLUDE   \epoc32\include\stdapis

LIBRARY       euser.lib
LIBRARY       libc.lib 

STATICLIBRARY libcrt0.lib

// fileaccessexample.h
//
// Copyright (C) Symbian Software Ltd 2007.  All rights reserved.

#ifndef __FILEACCESSEXAMPLE_H__
#define __FILEACCESSEXAMPLE_H__

// Declaration of functions defined in the source file.
void PressAKey();
int DisplayErrorMessage(char msg[]);
void CreateASecureDirectory();
void WriteDataToAFile(char FileName[]);
void ReadDataFromAFile(char FileName[]);
void RemoveADirectory(char FileName[]);
void WriteDataToFileOfAnotherProgram(char FileName[]);
void ReadDataFromFileOfAnotherProgram(char FileName[]);
void WriteDataToFileOfSysBin(char FileName[]);
void ReadDataToFileOfSysBin(char FileName[]);

#endif //__FILEACCESSEXAMPLE_H__

// fileaccessexample.c
//
// Copyright (C) Symbian Software Ltd 2007.  All rights reserved.

// This example demonstrates the Symbian OS platform security model.
// This shows the restrictions on the directories that can be accessed by a program, 
// depending on the capabilities that the program has.

// Include files
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>

/**
Waits for any key press 
*/
void PressAKey()
    {
    fflush(stdout);
    getchar();
    }
/**
Reports any error with error number.
@return EXIT_FAILURE Returns the failure code.
*/
int DisplayErrorMessage(char msg[])
    {
    printf("%s [Error NUMBER = %d]\n",msg,errno);
    PressAKey();
    return EXIT_FAILURE;
    }
/**
Create a secure directory for the program in the working directory of the process.
This is C:\private\<process UID>.
*/
void CreateASecureDirectory()
    {
    int result;
    
    /** 
    Call mkdir() function to create a directory named mydirectory in the working directory.
    It takes two parameters such as the name of the directory and mode to create it.
    This returns the value 0 if successful; otherwise the value -1 is returned.
    */ 
    result = mkdir("mydirectory",S_IWUSR);     
    if(result == 0)
        {
        printf(" A secure directory for the program is created successfully\n");
        PressAKey();
        }
    else
        {
        DisplayErrorMessage("\nError in creating directory\n");
        PressAKey();
        }
    }
/**
Write data to a file in the created directory.
@param FileName Path of the file to write to.
*/
void WriteDataToAFile(char FileName[])
    {
    FILE* fp= NULL;
    
    /**
    Call fopen() function to open the file.
    It takes two parameters, a string containing the file path, and the mode, set to 'w' to write data to it.
    It returns a file pointer if successful, otherwise NULL is returned.
    */
    fp = fopen(FileName, "w");
    if (fp== NULL)
        {
        DisplayErrorMessage("\nError in writing data in to the file=%d");
        PressAKey();
        }
    else
        {
        fprintf(fp,"%s","hello");
        fflush(fp);
        fclose(fp);
        printf(" Writing data in to the file from the secure directory is successful");
        }
    }

/**
Read data from a file in the created directory.
@param FileName Path of the file to read data from.
*/
void ReadDataFromAFile(char FileName[])
    {
    FILE* fp= NULL;
    
    /**
    Call fopen() function to open the file.
    It takes two parameters, a string containing the file path, and the mode, set to 'r' to read data from it.
    It returns a file pointer if successful, otherwise NULL is returned.
    */
    fp = fopen(FileName, "r");
    if (fp == NULL)
        {
         DisplayErrorMessage("\nError in reading data from the file = %d"); 
        printf(" Press any key to exit from the example");
          PressAKey();
        }
    else
        {
        char x[30];
                
        // Seek to the beginning of the file
       fseek(fp, SEEK_SET, 0); 
       
       // Get the data present in file from the beginning 
        fscanf(fp,"%s",x);
        printf("\n Data present in the file is : %s",x);
        fclose(fp);
        printf("\n Reading data of the file from the directory is successful\n");
        }
    }
/**
Remove the secure directory.
@param FileName Path of the file present in the directory.
*/
void RemoveADirectory(char FileName[])
    {
    int result;
    
    /**
    Call remove() function to remove the file specified in the path.
    It takes the parameter of a string containing the path of the file to remove.
    This returns the value 0 if successful; otherwise the value -1 is returned. 
    */
    result = remove(FileName);
    if(result == 0)
            {
            printf(" Removing the file from the directory is successful\n");
            }
        else
            {
            DisplayErrorMessage(" Error in removing the file from the directory=%d");
            PressAKey();
            }
    /**
    Call rmdir() function to remove a empty directory named mydirectory.
    Its parameter is the name of the directory to remove
    This returns the value 0 if successful; otherwise the value -1 is returned.
    */
    result = rmdir("mydirectory");
   
    if(result == 0)
        {
        printf(" Removing the the directory is successful\n");
        PressAKey();
        }
    else
        {
        DisplayErrorMessage(" Error in removing the directory=%d");
        PressAKey();
        }
    }
/**
Write data to a file in another program's private directory.
@param FileName Path of the file to write data to
*/
void WriteDataToFileOfAnotherProgram(char FileName[])
    {
    FILE* fp= NULL;
    
    /**
    Call fopen() function to open the file.
    It takes two parameters, a string containing the file path, and the mode, set to 'w' to write data to it.
    It returns a file pointer if successful, otherwise NULL is returned.
    */
    fp = fopen(FileName, "w");
    
    if (fp == NULL)
        {
        printf(" Writing data to files in a private directory belonging to another program is not possible"); 
          }
    else
        {
        printf("\n Writing data to files in a private directory belonging to another program is possible"); 
        PressAKey();
        }
    }
/**
Read data from a file in another program's private directory.
@param FileName Path of the file to read data from.
*/
void ReadDataFromFileOfAnotherProgram(char FileName[])
    {
    FILE* fp= NULL;
    
    /**
    Call fopen() function to open the file.
    It takes two parameters, a string containing the file path, and the mode, set to 'r' to read data from it
    It returns a file pointer if successful, otherwise NULL is returned.  
    */
    fp = fopen(FileName, "r");
    
    if (fp == NULL)
        {
        printf("\n Reading data from files in a private directory belonging to another program is not possible"); 
       PressAKey();
        }
    else
        {
         printf("\n Reading data from files in a private directory belonging to another program is possible"); 
        PressAKey(); 
        }
    }
/**
Write data to a file in the sys/bin directory.
@param FileName Path of the file to write data to.
*/
void WriteDataToFileOfSysBin(char FileName[])
    {
    FILE* fp= NULL;
    
    /**
    Call fopen() function to open the file.
    It takes two parameters, a string containing the file path, and the mode, set to 'w' to write data to it.
    It returns a file pointer if successful, otherwise NULL is returned.
    */
    fp = fopen(FileName, "w");
    
    if (fp == NULL)
        {
        printf("\n Writing data to files in the sys/bin directory is not possible"); 
        }
    else
        {
        printf("\n Writing data to files in the sys/bin directory is possible"); 
        PressAKey();
        }
    }
/**
Read data from a file in the sys/bin directory.
@param FileName Path of the file to read data from.
*/
void ReadDataToFileOfSysBin(char FileName[])
    {
    FILE* fp = NULL;
    
    /**
    Call fopen() function to open the file.
    It takes two parameters, a string containing the file path, and the mode, set to 'r' to read data from it.
    It returns a file pointer if successful, otherwise NULL is returned.
    */
    fp = fopen(FileName, "r");
    
    if (fp == NULL)
        {
        printf("\n Reading data from files in the sys/bin directory is not possible"); 
       PressAKey();
        }
    else
        {
         printf("\n Reading data from files in the sys/bin directory is possible"); 
         printf(" Press any key to exit from the example");
        PressAKey(); 
        }   
    }

int main()
{
    char ownFileName[50] = "\\private\\e80000c9\\mydirectory\\myownfile.txt";
    char otherFileName[40] = "\\private\\e80000c8\\otherfile.txt";
    char sysBinFileName[30] = "\\sys\\bin\\euser.dll";
    
    printf("\n Welcome to the file access example using POSIX APIs\n");
    
    // Print the message to start the example application.
    printf("\n Press enter key to step through the example\n");
    PressAKey();
    
    // Call CreateASecureDirectory() function to create a secure directory for the program.
    CreateASecureDirectory();
    
    // Call WriteDataToAFile() function to write data in to a file from the created directory.
    WriteDataToAFile(ownFileName);
    
    // Call WriteDataToAFile() function to write data in to a file from the created directory.
    ReadDataFromAFile(ownFileName);
    
    // Call RemoveADirectory() function to remove the directory.
    RemoveADirectory(ownFileName);
    
    // Call WriteDataToFileOfAnotherProgram() function to write data in to a file of another program.
    WriteDataToFileOfAnotherProgram(otherFileName);
    
    // Call ReadDataFromFileOfAnotherProgram() function to read data from a file of another program.
    ReadDataFromFileOfAnotherProgram(otherFileName);
    
    // Call WriteDataToFileOfSysBin() function to write data in to a file of sys/bin directory.
    WriteDataToFileOfSysBin(sysBinFileName);
    
    // Call ReadDataFromFileOfSysBin() function to read data from a file in the sys/bin directory.
    ReadDataToFileOfSysBin(sysBinFileName);
    
    // Print the message to exit from the example application.
    printf("\n Press enter key to exit from the example application");
    PressAKey();
    
    // returns the success code.
    return EXIT_SUCCESS;
}