Real world Linux programming

David M Williams
Tuesday, 11 December 2007 02:05

Opinion and Analysis

Finally, here is menu.c, the main program file for the menu application. This reads in the menu configuration file, displays a text-based menu on screen, prompts the user for input, then performs the appropriate command with privilege elevation if required.

/*
 * Simple menu program
 *
 *  David M. Williams
*/

#include "menu.h"

// ----------------------------------------------------------------------------
int main (int argc, char **argv)
{
 char  *username;
 char  *password;
 int  access = -1;
 ScriptTree theMenu = NULL;

#ifdef DISABLE_INTERRUPTS
 signal (SIGINT, SIG_IGN);
#endif

 username = (char *) malloc (sizeof (char) * 50);
 password = (char *) malloc (sizeof (char) * 10);

// Ask for a login

 login (username, password);

// Verify username and password, getting access level

 if (verify (username, password, &access) < 0)
  noAccess (username);
 else
 {

// Generate a list of menu options

  buildMenu (access, &theMenu);

// Repeatedly display menu and process input

  DoMenu (username, theMenu, 0);

// Tidy up

 }

 printf ("\nBye.\n");

 free (username);
 free (password);
 Destroy (theMenu);
}

// ----------------------------------------------------------------------------
void clrscrn ()
{
#ifdef CLEAR_SCREEN
 system ("/bin/clear");
#endif
}

// ----------------------------------------------------------------------------
void login (char *username, char *password)
{
 char tempPassword [10];

 clrscrn ();

#ifdef BANNER
 if (strlen (BANNER) > 0)
  puts (BANNER);
#endif

 printf ("   Login: ");
 scanf ("%s", username);

#ifdef HIDE_PASSWORD
 strcpy (tempPassword, getpass ("Password: "));
#else
 printf ("Password: ");
 scanf ("%s", tempPassword);
#endif

 log ("Login attempt by %s\t%s\n", username, tempPassword);

 strcpy (password, crypt (tempPassword, username));
}

// ----------------------------------------------------------------------------
void noAccess (char *username)
{
 clrscrn ();
 printf ("%s, you do not have permission to access this system\n"
  "or your password was wrong.\n", username);
}

// ----------------------------------------------------------------------------
int verify (char *username, char *password, int *access)
{
 FILE *fp;
 int Found = 0;
 char line [80];
 char tempUser [50];
 char tempPass [10];
 int tempAccess;

 *access = -1;

 if ((fp = fopen (USERLIST, "r")) > 0)
 {
  while ((!Found) && (!feof (fp)))
  {
   fgets (line, 80, fp);
   if ((line [0] != '\n') && (line [0] != '#'))
   {
    sscanf (line, "%s%s%d", tempUser, tempPass,
     &tempAccess);

    if ((strcmp (tempUser, username) == 0) &&
     (strcmp (tempPass, password) == 0))
    {
     Found = 1;
     *access = tempAccess;
    }
   }
  }

  fclose (fp);
 }
 else
  log ("Cannot open %s\n", USERLIST);

 log ("%s has an access level of %d\n", username, *access);

 return *access;
}

// ----------------------------------------------------------------------------
void buildMenu (int access, ScriptTree *theMenu)
{
 FILE  *fp;
 char  *line;
 char  *line2;
 char  *scriptName;
 char  *LineType;
 int  userLevel;
 int  useSudo;
 ScriptTree subMenu;

 line = (char *) malloc (sizeof (char) * 80);
 line2 = (char *) malloc (sizeof (char) * 80);
 scriptName = (char *) malloc (sizeof (char) * 80);
 LineType = (char *) malloc (sizeof (char) * 10);

 subMenu = *theMenu;

 if ((fp = fopen (MENULIST, "r")) > 0)
 {
  while (!feof (fp))
  {
   line [0] = '#';
   while (((line [0] == '\n') || (line [0] == '#')) &&
     (!feof (fp)))
    fgets (line, 80, fp);

   line2 [0] = '#';
   while (((line2 [0] == '\n') || (line2 [0] == '#')) &&
     (!feof (fp)))
    fgets (line2, 80, fp);

   if (!feof (fp))
   {
    sscanf (line, "%s", LineType);

    if (strcmp (LineType, "Menu") == 0)
    {
     sscanf (line, "%s%d", LineType,
      &userLevel);
     if (userLevel <= access)
      subMenu = AddMenu
       (theMenu, line2);
    }
    else if (strcmp (LineType, "Submenu") == 0)
    {
     sscanf (line, "%s%d", LineType,
      &userLevel);
     if (userLevel <= access)
      subMenu = AddMenu
       (&subMenu, line2);
    }
    else if (strcmp (LineType, "Option") == 0)
    {
     sscanf (line, "%s%d%d%s", LineType,
      &userLevel, &useSudo,
      scriptName);
     if (userLevel <= access)
      AddNode (&subMenu, line2,
       scriptName, useSudo);
    }
   }
  }

  fclose (fp);
 }
 else
  log ("Cannot open %s\n", MENULIST);

#ifdef DEBUGGING
 DumpMenu (0, *theMenu);
 exit (0);
#endif

 free (line);
 free (line2);
 free (scriptName);
 free (LineType);
}

// ----------------------------------------------------------------------------
void DoMenu (char *username, ScriptTree theMenu, int InSub)
{
 int  DoExit = 0;
 int  userChoice;
 int  MenuItems;

 while (!DoExit)
 {

// Display the menu

  MenuItems = DisplayMenu (theMenu, InSub);

// Get input

  userChoice = getChoice (MenuItems);

// Process command

  if (userChoice == 0)
   DoExit = 1;
  else
   ProcessChoice (userChoice, theMenu, username, InSub);
 }
}

// ----------------------------------------------------------------------------
ScriptTree AddMenu (ScriptTree *theMenu, char *ItemText)
{
// Make a new node
 ScriptTree aNode;

 aNode = (ScriptTree) malloc (sizeof (ScriptNode));
 strcpy (aNode->MenuText, ItemText);
 strcpy (aNode->ScriptName, "");
 aNode->Next = NULL;
 aNode->Submenu = NULL;

// Find the last node in the list and set its next pointer to this node.

 if (*theMenu == NULL)
  *theMenu = aNode;
 else
 {
  ScriptTree iterator = *theMenu;

  while (iterator->Submenu != NULL)
   iterator = (void *) iterator->Submenu;

  iterator->Submenu = aNode;
 }

 return aNode;
}

// ----------------------------------------------------------------------------
void AddNode (ScriptTree *theMenu, char *ItemText,
        char *ScriptCommand, int UseSudo)
{
// Make a new node
 ScriptTree aNode;

 aNode = (ScriptTree) malloc (sizeof (ScriptNode));
 strcpy (aNode->MenuText, ItemText);
 strcpy (aNode->ScriptName, ScriptCommand);
 aNode->RunAsRoot = UseSudo;
 aNode->Next = NULL;
 aNode->Submenu = NULL;

// Find the last node in the list and set its next pointer to this node.

 if (*theMenu == NULL)
  *theMenu = aNode;
 else
 {
  ScriptTree iterator = *theMenu;

  while (iterator->Next != NULL)
   iterator = (void *) iterator->Next;

  iterator->Next = aNode;
 }
}

// ----------------------------------------------------------------------------
void Destroy (ScriptTree theMenu)
{
 ScriptTree iterator = theMenu;

 if (iterator != NULL)
 {
  Destroy (iterator->Next);
  Destroy (iterator->Submenu);
  free (iterator);
 }
}

// ----------------------------------------------------------------------------
void DoCommand (char *username, char *ScriptName, int UseSudo)
{
 char c = ' ';
 char FullPath [PATH_MAX];

 puts ("\n\n");

 log ("%s is running %s %s sudo\n", username, ScriptName,
  (UseSudo ? "with" : "without"));

 if (strlen (ScriptName) > 0)
 {
  sprintf (FullPath, "%s/%s", SCRIPTSDIR, ScriptName);

  if (fork () == 0)
  {
#ifdef USE_EXECL
   if (UseSudo)
    execl (SUDO, SUDO, FullPath, NULL);
   else
    execl (FullPath, FullPath, NULL);
#else
   if (UseSudo)
   {
    char SudoCmnd [PATH_MAX];
    sprintf (SudoCmnd, "%s %s", SUDO, FullPath);
    system (SudoCmnd);
   }
   else
    system (FullPath);
#endif

   exit (0);
  }
#ifdef USE_EXECL
  else
  {
   int status;
          wait3 (&status, NULL, (struct rusage *) 0);
  }
#endif
 }

// Wait for a key to be pushed

 printf ("\n\n\tPlease press return : ");
 while (c != '\n')
  c = getchar ();
}

// ----------------------------------------------------------------------------
void log (const char *format, ...)
{
#ifdef LOGGING_ENABLED
        va_list args;
        char logmsg [255];
 FILE *fp;
 time_t now;
 char nowtime [30];
 
        va_start (args, format);
        vsprintf (logmsg, format, args);

 if ((fp = fopen (LOGFILE, "a")) > 0)
 {
  time (&now);
  strcpy (nowtime, ctime (&now));
  nowtime [strlen (nowtime) - 1] = '\0';
  fprintf (fp, "%s\t%s", nowtime, logmsg);
  fclose (fp);
 }

        va_end (args);
#endif
}

// ----------------------------------------------------------------------------
int DisplayMenu (ScriptTree theMenu, int InSub)
{
 int   MenuItems = 0;
 ScriptTree iterator;

 clrscrn ();

 if (!InSub)
  puts ("\tAdministrative services main menu");
 else
  printf ("\tAdministative sub-menu\n\t%s", theMenu->MenuText);

 puts ("\n\n");

 if (!InSub)
  puts ("\t0)\tExit the program\n");
 else
  puts ("\t0)\tExit this menu level\n");

 if (theMenu != NULL)
 {
  if (!InSub)
  {
   MenuItems = 1;
   printf ("\t1)\t%s", theMenu->MenuText);
  }

  if (!InSub)
  {
   iterator = (void *) theMenu->Submenu;
   while (iterator != NULL)
   {
    MenuItems++;
    printf ("\t%d)\t%s", MenuItems,
     iterator->MenuText);
    iterator = (void *) iterator->Submenu;
   }
  }
  else
  {
   iterator = (void *) theMenu->Next;
   while (iterator != NULL)
   {
    MenuItems++;
    printf ("\t%d)\t%s", MenuItems,
     iterator->MenuText);
    iterator = (void *) iterator->Next;
   }
  }
 }

 return MenuItems;
}

// ----------------------------------------------------------------------------
int getChoice (int MenuItems)
{
 int userChoice = -1;
 char temp [5];
 char c = ' ';

 do
 {
  printf ("\n\t\tChoice (0-%d) : ", MenuItems);
  scanf ("%s", temp);
  userChoice = atoi (temp);
 } while ((userChoice < 0) || (userChoice > MenuItems));

// Consume all remaining input
 while (c != '\n')
  c = getchar ();

 return userChoice;
}

// ----------------------------------------------------------------------------
void ProcessChoice (int userChoice, ScriptTree theMenu, char *username,
  int InSub)
{
 int  itemNum = 0;
 ScriptTree iterator = theMenu;
 ScriptTree theChoice = NULL;

 if (!InSub)
 {
  if (userChoice == 1)
   theChoice = theMenu;
  else
   itemNum = 1;
 }

 if ((theChoice == NULL) && (!InSub))
 {
  iterator = (void *) theMenu->Submenu;
  while ((iterator != NULL) && (theChoice == NULL))
  {
   itemNum++;
   if (userChoice == itemNum)
    theChoice = iterator;
   else
    iterator = (void *) iterator->Submenu;
  }
 }

 if ((theChoice == NULL) && (InSub))
 {
  iterator = (void *) theMenu->Next;
  while ((iterator != NULL) && (theChoice == NULL))
  {
   itemNum++;
   if (userChoice == itemNum)
    theChoice = iterator;
   else
    iterator = (void *) iterator->Next;
  }
 }

 if (theChoice == NULL)
  puts ("\nInvalid choice.\n");
 else
 {
  if (strcmp (theChoice->ScriptName, "") != 0)
   DoCommand (username, theChoice->ScriptName,
    theChoice->RunAsRoot);
  else
   DoMenu (username, theChoice, 1);
 }
}

// ----------------------------------------------------------------------------
void DumpMenu (int level, ScriptTree theMenu)
{
 ScriptTree iterator;

 if (theMenu != NULL)
 {
  indent (level);
  printf ("%d\t%s", level, theMenu->MenuText);

  level++;
  iterator = (void *) theMenu->Next;
  while (iterator != NULL)
  {
   indent (level);
   printf ("%d\t%s", level, iterator->MenuText);
   iterator = (void *) iterator->Next;
  }
  level--;

  iterator = (void *) theMenu->Submenu;
  while (iterator != NULL)
  {
   DumpMenu (level, iterator);
   iterator = (void *) iterator->Submenu;
  }
 }
}

// ----------------------------------------------------------------------------
void indent (int level)
{
 int i;

 for (i = 0; i < level * 2; i++)
  putchar (' ');
}