Receiving Segmentation Fault in basic reverse text C code - c

Question

I am using three files, my reverse.c, file_utils.h, and file_utils.c however after compiling successfully and executing I'm receiving a Segmentation Fault (core dumped). I'm unsure where the problem is. Thank you for any input!
Reverse.c File:
#include "file_utils.h"
#include <stdio.h>
#include <sys/stat.h>
//reverse function
//calls two parameters for a pointer to the input file and a pointer to the output file
//outputs the input file into the output in reverse
int reverse(char* inputFile, char* outputFile) {
char* buffer;
read_file(inputFile, &buffer);
struct stat st;
stat(inputFile, &st);
int size = st.st_size;
write_file(outputFile, buffer, size);
}
int main(int argc, char** argv[]) {
char* input;
char* output;
if(argv[1] != NULL) {
input = argv[1];
}
else {
printf("No input file detected.");
}
if(argv[2] != NULL) {
output = argv[2];
}
else {
printf("No output file detected.");
}
reverse(input, output);
}
file_utils.h Header:
#include <stdio.h>
void setup(int argc, char** argv);
int read_file( char* filename, char **buffer);
int write_file( char* filename, char *buffer, int size);
file_utils.c file:
#include "file_utils.h"
#include "stdlib.h"
//read_file function has two parameters which call a pointer to the input filenmae and
//a pointer to the pointer where the buffer will be stored
//returns the pointer to the newBuffer
int read_file( char* filename, char **buffer ) {
FILE *file;
file = fopen(filename, "r");
char* newBuffer = buffer;
int c;
size_t n = 0;
if(file == NULL) {
fprintf( stderr, "No file found. ");
return -1;
}
// length of file code found on stackoverflow.com/questions/4823177/reading-a-file
// given by user 'Justin'
fseek(file, 0, SEEK_END);
long f_size = ftell(file);
fseek(file, 0, SEEK_SET);
buffer = malloc(f_size);
if(newBuffer == NULL || newBuffer < 0) {
fprintf(stderr, "Memory allocation error. ");
}
while((c = fgetc(file)) != EOF) {
newBuffer[n++] = (char) c;
}
newBuffer[n] = '\0';
return *newBuffer;
}
//write_file function has three parameters which consist of a pointer to the output file,
//the actual value of the buffer pointer, and the size of the buffer
int write_file( char* filename, char *buffer, int size) {
fwrite(buffer, sizeof(char), size, filename);
}