Question

Fix the code below to make it so that it is not vulernable to stack buffer overflow

void gctinp (ohar *inp, int siz) puts ("Input value: ") fgets (inp, siz, stdin) printf("buffer3 getinp read %s\n", inp); void display (char val) char tmp [16]; sprintf(tmp, "read val : puts (tmp); %s\n", val); int main(int argc, char *argv []) char buf [16]; getinp (buf, sizeof (buf)) display (buf); printf ("buffer3 done In")

Answer 1

Program code screenshot:

// Declare the required header file #include <stdio.h> #include <string.h> #include <stdlib.h> // ****** Modify this function ******* // // Declare the get input function void gctinp(char * inp, int siz) { // Declare the required variables char * input_string; int count = 0; char c; // Ask from the user to // prompt the input value puts ("Input value: "); scanf("%c", &c); // while loop to check the condition while(c != '\n') // check the stack count is equal to 16 if(count == 16) // Display the message stack is over floe printf("ERROR: Stack Overflow!!\n"); return; // When stack is zero if (count == 0) // input the string size input_string = (char *)malloc(sizeof(char)*1); // otherwise else // increment the stack size input_string = (char*)realloc(input_string, sizeof(char)* count+1); // assign the stack char input_string[count] = c; // increment the stack count++; // display the stack scanf("%c", &c); // copy the stack size strcpy(inp, input string); } // Create a display function void display(char * val) // Declare the required char array temp char temp[16]; // Display the message sprintf(temp, "read value: %s \n", val); // puts the temp value puts (temp); // Create a main function of the program int main() // Declare the required variables char buf[16]; // call the gctinp function gctinp(buf, sizeof(buf)); // Display the function display (buf); // Display message buffer is done printf("Buffer Done");
Sample output:

111) ? clang-7 -pthread -lm -o main main.c } ./main Input value: Sunny day read value: Sunny day Buffer Done

? clang-7 -pthread -lm -o main main.c ./main Input value: If you want your children to listen, try talking softly to someone else ERROR: Stack OverFlow!! read value: @@ Buffer Done

Program code to copy:

// Declare the required header file

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

// ****** Modify this function ******* //

// Declare the get input function

void gctinp(char * inp, int siz)

{

    // Declare the required variables

    char * input_string;

    int count = 0;

    char c;

    // Ask from the user to

    // prompt the input value

    puts("Input value: ");

    scanf("%c", &c);

    // while loop to check the condition

    while(c != '\n')

    {

        // check the stack count is equal to 16

        if(count == 16)

        {

            // Display the message stack is over floe

            printf("ERROR: Stack OverFlow!!\n");

            return;

        }

        // When stack is zero

        if (count == 0)

        {

            // input the string size

            input_string = (char *)malloc(sizeof(char)*1);

        }

        // otherwise

        else

        {

            // increment the stack size

            input_string = (char*)realloc(input_string, sizeof(char)*count+1);

        }

        // assign the stack char

        input_string[count] = c;

        // increment the stack

        count++;

        // display the stack

        scanf("%c", &c);

    }

  

     // copy the stack size

    strcpy(inp, input_string);

}

// Create a display function

void display(char * val)

{

// Declare the required char array temp

    char temp[16];

    // Display the message

    sprintf(temp,"read value: %s \n",val);

    // puts the temp value

    puts(temp);

}

// Create a main function of the program

int main()

{

// Declare the required variables

    char buf[16];

    // call the gctinp function

    gctinp(buf,sizeof(buf));

    // Display the function

    display(buf);

    // Display message buffer is done

    printf("Buffer Done");

}