Invalid write of Size 8 when mallocing array of strings - c

Question

I am trying to write my own Shell in C. I have a problem. I wrote my own _strtok function that uses strtok but returns all the tokens as an array of strings. For testing I use the string "ls -laR" defined in the main function. I get the valgrind error "Invalid write of size 8" when trying to malloc the number of chars in the second pointer in the array of strings named "Doubl". Why is it doing this? I am allocating the proper number of pointers to strings in the doubl array. Any insight or help would be appreciated
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
char **_strtok(char *str, char *delim)
{
char **doubl;
char *s = str;
char *string;
int i = 0;
while (*s)
{
if (*s == *delim)
i++;
s++;
}
doubl = malloc(sizeof(char *) * i + 1);
i = 0;
string = strtok(str, delim);
while (1)
{
doubl[i] = malloc(sizeof(char) * strlen(string) + 1);
strcpy(doubl[i], string);
i++;
if (string == NULL)
break;
string = strtok(NULL, delim);
}
return (doubl);
}
char *get_path(char **env)
{
char **check = env;
char *path = NULL;
char pth[] = "PATH";
int i, j, stop = 0;
for (i = 0; check[i] && stop == 0; i++)
{
for (j = 0; j < 4 && stop == 0; j++)
{
if (check[i][j] != pth[j])
break;
if (check[i][j] == pth[j] && j == 3)
{
path = malloc(strlen(check[i]));
strcpy(path, check[i]);
stop = 1;
}
}
}
return (path);
}
char **cmd_to_arg(char **cmd, char **env)
{
/* FREE PATH BEFORE END */
char *path = get_path(env);
char *slash = "/";
char **args = NULL, **check = _strtok(path, ":"), **checkStart = check, **cmdStart = cmd;
int status = -1, i = 0, j;
while (*checkStart)
{
strcat(*checkStart, slash);
strcat(*checkStart, cmd[0]);
status = access(*checkStart, F_OK | X_OK);
printf("%s\n", *checkStart);
if (status == 0)
break;
checkStart++;
}
for(;*cmdStart; i++, cmdStart++)
printf("%d\n", i);
args = malloc(sizeof(char *) * i);
args[0] = malloc(strlen(*checkStart));
strcpy(args[0], *checkStart);
puts(args[0]);
for (j = 1; j < i && cmd[j] != NULL; j++)
{
//printf("%d\n", j);
args[j] = malloc(strlen(cmd[j]) * sizeof(char));
strcpy(args[j], cmd[j]);
puts(args[j]);
}
return (args);
}
int main(int ac, char **av, char **env)
{
(void)ac, (void)av, (void)env;
char line[] = "ls laR";
//size_t size = 0;
char **cmd; //**cmdStart;
//int i = 0, j = 0;
cmd = _strtok(line, " ");
cmd = cmd_to_arg(cmd, env);
return (0);
}