Program doesn't segfault only when stepping through debugger (gdb) - c

Question

This program I wrote to automatically turn my network's auto configuration logic only segfaults if I run through the program without breaking. When running through a debugger with breakpoints, it runs perfectly fine. When run through a debugger without breakpoints, it segfaults. Is there a bug in this program that I'm not noticing?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define COMLEN 64
#define BUFSIZE 128
const char *program_name;
typedef enum errors
{
SUCCESS = 0,
MEM_ERROR,
FILE_ERROR,
USAGE_ERROR,
} Error;
void terminal_error(Error e)
{
switch (e)
{
case MEM_ERROR:
fputs("Memory error!\n", stderr);
break;
case FILE_ERROR:
fputs("File error!\n", stderr);
break;
case USAGE_ERROR:
fprintf(stderr, "Incorrect usage. Try %s [y|n]\n", program_name);
break;
default:
fputs("Unknown error!\n", stderr);
break;
}
exit(e);
}
Error read_file(FILE *fp, char **buffer)
{
long len;
fseek(fp, 0, SEEK_END);
len = ftell(fp);
fseek(fp, 0, SEEK_SET);
if ((*buffer = malloc(len+1)) == NULL)
return MEM_ERROR;
if (fread(*buffer, 1, len, fp) != len)
return FILE_ERROR;
buffer[len+1] = '\0';
return SUCCESS;
}
Error get_interface(char *name)
{
const char *cmd = "netsh wlan show networks";
FILE *fp;
// open pipe to parse output from command and run command
if ((fp = popen(cmd, "rb")) == NULL)
return FILE_ERROR;
// read the piped output into buffer
char *buffer = NULL;
Error res;
res = read_file(fp, &buffer);
if (res != SUCCESS)
return res;
fclose(fp);
// parse the buffer
// needle delimits the start of the interface name in the command
// end_needle delimits the end of the interface name
const char *needle = "Interface name : ";
const char *end_needle = " \r\nThere";
// end will point to end_needle (end of interface name)
char *end = NULL;
// name points to one-past the end of the needle (start of interface
// name)
name = strstr(buffer, needle);
name += strlen(needle);
end = strstr(buffer, end_needle);
*end = '\0'; // terminates the interface name
return SUCCESS;
}
int main(int argc, const char *argv[])
{
const char *template = "netsh wlan set autoconfig enabled=%s interface=\"%s\"";
char interface_name[BUFSIZE] = {0};
program_name = argv[0];
Error res = SUCCESS;
// get name of wireless interfacew
res = get_interface(interface_name);
if (res != SUCCESS)
terminal_error(res);
char *op;
if (argc > 1)
// arguments were provided
{
if (strcmp(argv[1], "y") == 0)
op = "yes";
else if (strcmp(argv[1], "n") == 0)
op = "no";
else
terminal_error(USAGE_ERROR);
char command[COMLEN];
sprintf(command, template, op, interface_name);
system(command);
}
else
// no arguments were provided
{
system("netsh wlan show settings");
}
return 0;
}