Write two library functions in C programming language for system calls (A setter

Question

Write two library functions in C programming language for system calls (A setter method for setting the security tag value in Linux) and (A getter method for getting the security tag value in Linux)

int set_security_tag(const char *filename, int new_tag)

{

// Invokes the system call which attempts to change the file's Security_Tag to new_tag

// Returns the changed Security_Tag on success, otherwise it returns "-1"

}

int get_security_tag(const char *filename)

{

// Invokes a system call which reads the security tag of the input file

// It will return Security_Tag upon success; otherwise it will return a value of "-1"

}

Explanation / Answer

Answer: See the code below:

----------------------------------------------------

#include <sys/types.h>
#include <sys/xattr.h>
#include <stdio.h>
#include <stdlib.h>

//set_security_tag function
int set_security_tag(const char *filename, int new_tag)
{
   int status;
   status=setxattr(filename, "Security_Tag", &new_tag, sizeof(new_tag), 0);
   if (status==0)
       return new_tag;
   else
       return -1;
}

//get_security_tag function
int get_security_tag(const char *filename)
{

   ssize_t sz; //size of value of attribute
   int* value; //value of attribute
   //determine size of value of attribute
   sz=getxattr(filename,"Security_Tag",NULL,0);
  
   //check if ok
   if (sz == -1)
       fprintf(stderr,"error in extracting size. ");
   //allocate space for value of attribute
   if (sz > 0)
   {
       value = (int*)malloc(sizeof(int));
       //get value of attribute
       sz = getxattr(filename, "Security_Tag", value, sz);
       if (sz == -1)
           return -1;
       else
           return *value;
   }
}

//main function
int main()
{
   char* filename = "./tlpi_hdr.h"; //example file
   int new_tag = 2; //value of security tag
   //setting security tag
   new_tag = set_security_tag(filename,new_tag);
   if(new_tag!=-1)
       printf("Security tag set successfully ");
   else
       printf("Security tag not set successfully ");
  
   //getting security tag
   new_tag = get_security_tag(filename);
   if(new_tag!=-1)
       printf("Security tag retrieved successfully: %d ",new_tag);
   else
       printf("Security tag not retrieved successfully: %d ",new_tag);
   return EXIT_SUCCESS;
}

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