Execute shellcode from file using mmap()

shellcode_mmap.c

/*
 * Exec shellcode from file
 *   gcc ./shellcode_mmap.c -o ./shellcode_mmap
 *
 * Sat Jul  1 20:21:12 CEST 2023
 * [email protected]
 *
 * 1. Create a payload:
 *   msfvenom -p osx/x64/exec CMD=/bin/sh -f raw -o osx-exec.raw
 *
 * 2. Execute it
 *   $ ./shellcode_mmap osx-exec.raw
 *   Reading payload from osx-exec.raw
 *   File size is 31
 *   Length of shellcode: 31
 *   sh-3.2$
 *
 */

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>
#include <errno.h>

int (*sc)();

int main(int argc, char **argv) {

    char *shellcode = NULL;
    char *filepath = NULL;
    void *ptr = NULL;
    struct stat statbuf;
    short int fd;
    size_t offset;
    size_t size;
    ssize_t result;


    if (argc != 2){
        printf("Usage: %s <payload file>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    filepath = argv[1];

    printf("Reading payload from %s\n", filepath);

    if ((fd = open(filepath, O_RDONLY)) < 0){
        perror("open() failed");
        exit(EXIT_FAILURE);
    }


    if (fstat (fd, &statbuf) < 0){
        perror("fstat() failed");
        close(fd);
        exit(EXIT_FAILURE);
    }

    printf("File size is %lld\n", statbuf.st_size);

    if ( (ptr = mmap(NULL, statbuf.st_size, PROT_WRITE | PROT_EXEC,
                    MAP_FILE | MAP_PRIVATE, fd, 0)) == MAP_FAILED ){
        perror("mmap() failed");
        close(fd);
        exit(EXIT_FAILURE);
    }

    sc = ptr;
    sc();

    if (munmap(ptr, statbuf.st_size) == -1){
        perror("munmao() failed");
    }

    close(fd);

    exit (EXIT_SUCCESS);
}