Segfault from execvp - c

Question

I'm trying to exec input that I get from a socket. I take the message buffer and put it into a char *[] and it is null terminated it works for ls but it won't work with paramaters like ls -la.
char *CMD[msg.c+1];
CMD[msg.c] = NULL;
Here is me parsing and using execvp.
//parse
char *tmp = NULL;
tmp = strtok(msg.v,space);
for(i = 0; i < msg.c; i++){
CMD[i] = tmp;
tmp = strtok(NULL,space);
printf("%s\n",CMD[i]);
}
int fd[2];
pipe(fd);
pid_t pid = fork();
if (pid == 0) {
close(fd[0]);
dup2(fd[1], 1);
msg.c = execvp(CMD[0],CMD);
}

Answer 1

This is probably so late answer that no one cares... To summarise there are some issues in your program, but I do not really know why you got segmentation fault or if you already fixed that.
In the code:
use of strsep(3) instead of obsolete strtok(3)
strdup(3) to be sure no other code modifies msg, if not, then you can remove strdup and free
added some error handling with err(3) to find errors early (earlier).
you cannot do msg.c = execvp(CMD[0], CMD), the program is executing CMD and will never return; to be able to retrieve the exit code, use wait(2) or waitpid(2)
variable length of arrays (char *CMD[msg.c+1]) is allowed in C99, but I do not use it, you can if you want. :)
And here is the lengthy code, probably a lot of bugs, but please tell me and I will try to fix:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <err.h>
#include <sys/types.h>
#include <sys/wait.h>
#define MAX_ARGS 10
int
main(int argc, char *argv[])
{
char *cmd[MAX_ARGS];
char *s;
char buf[256];
char msg[] = "ls -la /";
int n;
int fd[2];
pid_t pid;
int stat;
if ((s = strdup(msg)) == NULL)
err(1, "strdup");
for (n = 0; n < MAX_ARGS && (cmd[n] = strsep(&s, " ")) != NULL; n++)
;
if (pipe(fd) == -1)
err(1, "pipe");
switch ((pid = fork())) {
case -1:
close(fd[0]);
close(fd[1]);
err(1, "fork");
case 0: /* child */
close(fd[0]);
dup2(fd[1], STDOUT_FILENO);
close(fd[1]);
execvp(cmd[0], cmd);
err(1, "execvp");
default: /* parent */
free(s);
close(fd[1]);
while ((n = read(fd[0], buf, sizeof(buf))) > 0)
write(STDOUT_FILENO, buf, n);
waitpid(pid, &stat, 0);
fprintf(stderr, "child(%d) exited with %d\n",
pid, WEXITSTATUS(stat));
}
return (0);
}