Daniel Lezcano <daniel.lezcano@xxxxxxx> writes:
> Eric W. Biederman wrote:
>
> [ ... ]
>> I guess my meaning is I was expecting.
>> child = fork();
>> if (child == 0) {
>> execve(...);
>> }
>> waitpid(child);
>>
>> This puts /bin/sh in the container as well.
>>
> #include <unistd.h>
> #include <stdlib.h>
> #include <stdio.h>
> #include <syscall.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <sys/param.h>
>
> #define __NR_setns 300
>
> int setns(int nstype, int fd)
> {
> return syscall (__NR_setns, nstype, fd);
> }
>
> int main(int argc, char *argv[])
> {
> char path[MAXPATHLEN];
> char *ns[] = { "pid", "mnt", "net", "pid", "uts" };
> const int size = sizeof(ns) / sizeof(char *);
> int fd[size];
> int i;
> pid_t pid;
> if (argc != 3) {
> fprintf(stderr, "mynsenter <pid> <command>\n");
> exit(1);
> }
>
> for (i = 0; i < size; i++) {
> sprintf(path, "/proc/%s/ns/%s", argv[1], ns[i]);
>
> fd[i] = open(path, O_RDONLY| FD_CLOEXEC);
> if (fd[i] < 0) {
> perror("open");
> return -1;
> }
>
> }
> for (i = 0; i < size; i++)
> if (setns(0, fd[i])) {
> perror("setns");
> return -1;
> }
>
> pid = fork();
> if (!pid) {
>
> fprintf(stderr, "mypid is %d\n", syscall(__NR_getpid));
>
> execve(argv[2], &argv[2], NULL);
> perror("execve");
>
> }
>
> if (pid < 0) {
> perror("fork");
> return -1;
> }
>
> if (waitpid(&pid, NULL, 0) < 0) {
> perror("waitpid");
> }
>
> return 0;
> }
&pid ??? Isn't that a type error?
> Waitpid returns an error:
>
> waitpid: No child processes
>
> The pid number returned by fork is the pid from the init pid namespace but it
> seems waitpid is waiting for a pid belonging to the child pid namespace.
>
> waitpid
> -> wait4
> -> find_get_pid
> -> find_vpid
> -> find_pid_ns(nr, current->nsproxy->pid_ns);
But it isn't. It is.
find_pid_ns(nr, task_active_pid_ns(current));
Which is:
find_pid_ns(nr, ns_of_pid(task_pid(current)));
Which is a value that doesn't change. When we attach to a pid namespace.
> The current->nsproxy->pid_ns is the one of the namespace we attached to. So the
> real pid returned by the fork does not exist in this pid namespace.
> Maybe fork should return a pid number belonging to the current pid namespace we
> are attached no ?
Do you not have my patch that changed that?
Eric
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