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#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/stat.h>
#include <limits.h>
#include <sys/types.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <string.h>
static const char *_max_user_namespaces = "/proc/sys/user/max_user_namespaces";
static const char *_unprivileged_user_namespaces = "/proc/sys/kernel/unprivileged_userns_clone";
static int
syscall_setresuid (uid_t ruid, uid_t euid, uid_t suid)
{
return (int) syscall (__NR_setresuid, ruid, euid, suid);
}
static int
syscall_setresgid (gid_t rgid, gid_t egid, gid_t sgid)
{
return (int) syscall (__NR_setresgid, rgid, egid, sgid);
}
static int
syscall_clone (unsigned long flags, void *child_stack)
{
return (int) syscall (__NR_clone, flags, child_stack);
}
static char **
get_cmd_line_args (pid_t pid)
{
int fd;
char path[PATH_MAX];
char *buffer;
size_t allocated;
size_t used = 0;
int ret;
int i, argc = 0;
char **argv;
sprintf (path, "/proc/%d/cmdline", pid);
fd = open (path, O_RDONLY);
if (fd < 0)
return NULL;
allocated = 512;
buffer = malloc (allocated);
if (buffer == NULL)
return NULL;
for (;;)
{
do
ret = read (fd, buffer + used, allocated - used);
while (ret < 0 && errno == EINTR);
if (ret < 0)
return NULL;
if (ret == 0)
break;
used += ret;
if (allocated == used)
{
allocated += 512;
buffer = realloc (buffer, allocated);
if (buffer == NULL)
return NULL;
}
}
close (fd);
for (i = 0; i < used; i++)
if (buffer[i] == '\0')
argc++;
if (argc == 0)
return NULL;
argv = malloc (sizeof (char *) * (argc + 1));
if (argv == NULL)
return NULL;
argc = 0;
argv[argc++] = buffer;
for (i = 0; i < used - 1; i++)
if (buffer[i] == '\0')
argv[argc++] = buffer + i + 1;
argv[argc] = NULL;
return argv;
}
int
reexec_userns_join (int userns, int mountns)
{
pid_t ppid = getpid ();
char uid[16];
char **argv;
int pid;
sprintf (uid, "%d", geteuid ());
argv = get_cmd_line_args (ppid);
if (argv == NULL)
{
fprintf (stderr, "cannot read argv: %s\n", strerror (errno));
_exit (EXIT_FAILURE);
}
pid = fork ();
if (pid < 0)
fprintf (stderr, "cannot fork: %s\n", strerror (errno));
if (pid)
return pid;
setenv ("_LIBPOD_USERNS_CONFIGURED", "init", 1);
setenv ("_LIBPOD_ROOTLESS_UID", uid, 1);
if (setns (userns, 0) < 0)
{
fprintf (stderr, "cannot setns: %s\n", strerror (errno));
_exit (EXIT_FAILURE);
}
close (userns);
if (mountns >= 0 && setns (mountns, 0) < 0)
{
fprintf (stderr, "cannot setns: %s\n", strerror (errno));
_exit (EXIT_FAILURE);
}
close (userns);
if (syscall_setresgid (0, 0, 0) < 0)
{
fprintf (stderr, "cannot setresgid: %s\n", strerror (errno));
_exit (EXIT_FAILURE);
}
if (syscall_setresuid (0, 0, 0) < 0)
{
fprintf (stderr, "cannot setresuid: %s\n", strerror (errno));
_exit (EXIT_FAILURE);
}
execvp (argv[0], argv);
_exit (EXIT_FAILURE);
}
static void
check_proc_sys_userns_file (const char *path)
{
FILE *fp;
fp = fopen (path, "r");
if (fp)
{
char buf[32];
size_t n_read = fread (buf, 1, sizeof(buf) - 1, fp);
if (n_read > 0)
{
buf[n_read] = '\0';
if (strtol (buf, NULL, 10) == 0)
fprintf (stderr, "user namespaces are not enabled in %s\n", path);
}
fclose (fp);
}
}
int
reexec_in_user_namespace (int ready)
{
int ret;
pid_t pid;
char b;
pid_t ppid = getpid ();
char **argv;
char uid[16];
sprintf (uid, "%d", geteuid ());
pid = syscall_clone (CLONE_NEWUSER|CLONE_NEWNS|SIGCHLD, NULL);
if (pid < 0)
{
FILE *fp;
fprintf (stderr, "cannot clone: %s\n", strerror (errno));
check_proc_sys_userns_file (_max_user_namespaces);
check_proc_sys_userns_file (_unprivileged_user_namespaces);
}
if (pid)
return pid;
argv = get_cmd_line_args (ppid);
if (argv == NULL)
{
fprintf (stderr, "cannot read argv: %s\n", strerror (errno));
_exit (EXIT_FAILURE);
}
setenv ("_LIBPOD_USERNS_CONFIGURED", "init", 1);
setenv ("_LIBPOD_ROOTLESS_UID", uid, 1);
do
ret = read (ready, &b, 1) < 0;
while (ret < 0 && errno == EINTR);
if (ret < 0)
{
fprintf (stderr, "cannot read from sync pipe: %s\n", strerror (errno));
_exit (EXIT_FAILURE);
}
close (ready);
if (syscall_setresgid (0, 0, 0) < 0)
{
fprintf (stderr, "cannot setresgid: %s\n", strerror (errno));
_exit (EXIT_FAILURE);
}
if (syscall_setresuid (0, 0, 0) < 0)
{
fprintf (stderr, "cannot setresuid: %s\n", strerror (errno));
_exit (EXIT_FAILURE);
}
execvp (argv[0], argv);
_exit (EXIT_FAILURE);
}
int
reexec_in_user_namespace_wait (int pid)
{
pid_t p;
int status;
do
p = waitpid (pid, &status, 0);
while (p < 0 && errno == EINTR);
if (p < 0)
return -1;
if (WIFEXITED (status))
return WEXITSTATUS (status);
if (WIFSIGNALED (status))
return 128 + WTERMSIG (status);
return -1;
}
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