blob: b93f827b55fc7dabb7c2256471f4e5f53fce921d [file] [log] [blame]
#define _GNU_SOURCE
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <sched.h>
#include <setjmp.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/prctl.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <linux/limits.h>
#include <linux/netlink.h>
#include <linux/types.h>
#define SYNC_VAL 0x42
#define JUMP_VAL 0x43
/* Assume the stack grows down, so arguments should be above it. */
struct clone_arg {
/*
* Reserve some space for clone() to locate arguments
* and retcode in this place
*/
char stack[4096] __attribute__ ((aligned(16)));
char stack_ptr[0];
jmp_buf *env;
};
struct nlconfig_t {
char *data;
uint32_t cloneflags;
char *uidmap;
int uidmap_len;
char *gidmap;
int gidmap_len;
uint8_t is_setgroup;
int consolefd;
};
/*
* List of netlink message types sent to us as part of bootstrapping the init.
* These constants are defined in libcontainer/message_linux.go.
*/
#define INIT_MSG 62000
#define CLONE_FLAGS_ATTR 27281
#define CONSOLE_PATH_ATTR 27282
#define NS_PATHS_ATTR 27283
#define UIDMAP_ATTR 27284
#define GIDMAP_ATTR 27285
#define SETGROUP_ATTR 27286
/*
* Use the raw syscall for versions of glibc which don't include a function for
* it, namely (glibc 2.12).
*/
#if __GLIBC__ == 2 && __GLIBC_MINOR__ < 14
# define _GNU_SOURCE
# include "syscall.h"
# if !defined(SYS_setns) && defined(__NR_setns)
# define SYS_setns __NR_setns
# endif
#ifndef SYS_setns
# error "setns(2) syscall not supported by glibc version"
#endif
int setns(int fd, int nstype)
{
return syscall(SYS_setns, fd, nstype);
}
#endif
/* TODO(cyphar): Fix this so it correctly deals with syncT. */
#define bail(fmt, ...) \
do { \
fprintf(stderr, "nsenter: " fmt ": %m\n", ##__VA_ARGS__); \
exit(__COUNTER__ + 1); \
} while(0)
static int child_func(void *arg)
{
struct clone_arg *ca = (struct clone_arg *)arg;
longjmp(*ca->env, JUMP_VAL);
}
static int clone_parent(jmp_buf *env, int flags) __attribute__ ((noinline));
static int clone_parent(jmp_buf *env, int flags)
{
int child;
struct clone_arg ca = {
.env = env,
};
child = clone(child_func, ca.stack_ptr, CLONE_PARENT | SIGCHLD | flags, &ca);
/*
* On old kernels, CLONE_PARENT didn't work with CLONE_NEWPID, so we have
* to unshare(2) before clone(2) in order to do this. This was fixed in
* upstream commit 1f7f4dde5c945f41a7abc2285be43d918029ecc5, and was
* introduced by 40a0d32d1eaffe6aac7324ca92604b6b3977eb0e.
*
* As far as we're aware, the last mainline kernel which had this bug was
* Linux 3.12. However, we cannot comment on which kernels the broken patch
* was backported to.
*/
if (errno == EINVAL) {
if (unshare(flags) < 0)
bail("unable to unshare namespaces");
child = clone(child_func, ca.stack_ptr, SIGCHLD | CLONE_PARENT, &ca);
}
return child;
}
/*
* Gets the init pipe fd from the environment, which is used to read the
* bootstrap data and tell the parent what the new pid is after we finish
* setting up the environment.
*/
static int initpipe(void)
{
int pipenum;
char *initpipe, *endptr;
initpipe = getenv("_LIBCONTAINER_INITPIPE");
if (initpipe == NULL || *initpipe == '\0')
return -1;
errno = 0;
pipenum = strtol(initpipe, &endptr, 10);
if (errno != 0 || *endptr != '\0')
bail("unable to parse _LIBCONTAINER_INITPIPE");
return pipenum;
}
static uint32_t readint32(char *buf)
{
return *(uint32_t *) buf;
}
static uint8_t readint8(char *buf)
{
return *(uint8_t *) buf;
}
static int write_file(char *data, size_t data_len, char *pathfmt, ...)
{
int fd, len, ret = 0;
char path[PATH_MAX];
va_list ap;
va_start(ap, pathfmt);
len = vsnprintf(path, PATH_MAX, pathfmt, ap);
va_end(ap);
if (len < 0)
return -1;
fd = open(path, O_RDWR);
if (fd < 0) {
ret = -1;
goto out;
}
len = write(fd, data, data_len);
if (len != data_len) {
ret = -1;
goto out;
}
out:
close(fd);
return ret;
}
#define SETGROUPS_ALLOW "allow"
#define SETGROUPS_DENY "deny"
/* This *must* be called before we touch gid_map. */
static void update_setgroups(int pid, bool setgroup)
{
char *policy;
if (setgroup)
policy = SETGROUPS_ALLOW;
else
policy = SETGROUPS_DENY;
if (write_file(policy, strlen(policy), "/proc/%d/setgroups", pid) < 0) {
/*
* If the kernel is too old to support /proc/pid/setgroups,
* open(2) or write(2) will return ENOENT. This is fine.
*/
if (errno != ENOENT)
bail("failed to write '%s' to /proc/%d/setgroups", policy, pid);
}
}
static void update_uidmap(int pid, char *map, int map_len)
{
if (map == NULL || map_len <= 0)
return;
if (write_file(map, map_len, "/proc/%d/uid_map", pid) < 0)
bail("failed to update /proc/%d/uid_map", pid);
}
static void update_gidmap(int pid, char *map, int map_len)
{
if (map == NULL || map_len <= 0)
return;
if (write_file(map, map_len, "/proc/%d/gid_map", pid) < 0)
bail("failed to update /proc/%d/gid_map", pid);
}
#define JSON_MAX 4096
static void start_child(int pipenum, jmp_buf *env, int syncpipe[2], struct nlconfig_t *config)
{
int len, childpid;
char buf[JSON_MAX];
uint8_t syncval;
/*
* We must fork to actually enter the PID namespace, and use
* CLONE_PARENT so that the child init can have the right parent
* (the bootstrap process). Also so we don't need to forward the
* child's exit code or resend its death signal.
*/
childpid = clone_parent(env, config->cloneflags);
if (childpid < 0)
bail("unable to fork");
/* Update setgroups, uid_map and gid_map for the process if provided. */
if (config->is_setgroup)
update_setgroups(childpid, true);
update_uidmap(childpid, config->uidmap, config->uidmap_len);
update_gidmap(childpid, config->gidmap, config->gidmap_len);
/* Send the sync signal to the child. */
close(syncpipe[0]);
syncval = SYNC_VAL;
if (write(syncpipe[1], &syncval, sizeof(syncval)) != sizeof(syncval))
bail("failed to write sync byte to child");
/* Send the child pid back to our parent */
len = snprintf(buf, JSON_MAX, "{\"pid\": %d}\n", childpid);
if (len < 0 || write(pipenum, buf, len) != len) {
kill(childpid, SIGKILL);
bail("unable to send a child pid");
}
exit(0);
}
static void nl_parse(int fd, struct nlconfig_t *config)
{
size_t len, size;
struct nlmsghdr hdr;
char *data, *current;
/* Retrieve the netlink header. */
len = read(fd, &hdr, NLMSG_HDRLEN);
if (len != NLMSG_HDRLEN)
bail("invalid netlink header length %lu", len);
if (hdr.nlmsg_type == NLMSG_ERROR)
bail("failed to read netlink message");
if (hdr.nlmsg_type != INIT_MSG)
bail("unexpected msg type %d", hdr.nlmsg_type);
/* Retrieve data. */
size = NLMSG_PAYLOAD(&hdr, 0);
current = data = malloc(size);
if (!data)
bail("failed to allocate %zu bytes of memory for nl_payload", size);
len = read(fd, data, size);
if (len != size)
bail("failed to read netlink payload, %lu != %lu", len, size);
/* Parse the netlink payload. */
config->data = data;
config->consolefd = -1;
while (current < data + size) {
struct nlattr *nlattr = (struct nlattr *)current;
size_t payload_len = nlattr->nla_len - NLA_HDRLEN;
/* Advance to payload. */
current += NLA_HDRLEN;
/* Handle payload. */
switch (nlattr->nla_type) {
case CLONE_FLAGS_ATTR:
config->cloneflags = readint32(current);
break;
case CONSOLE_PATH_ATTR:
/*
* The context in which this is done (before or after we
* join the other namespaces) will affect how the path
* resolution of the console works. This order is not
* decided here, but rather in container_linux.go. We just
* follow the order given by the netlink message.
*/
config->consolefd = open(current, O_RDWR);
if (config->consolefd < 0)
bail("failed to open console %s", current);
break;
case NS_PATHS_ATTR:{
/*
* Open each namespace path and setns it in the
* order provided to us. We currently don't have
* any context for what kind of namespace we're
* joining, so just blindly do it.
*/
char *saveptr = NULL;
char *ns = strtok_r(current, ",", &saveptr);
int *fds = NULL, num = 0, i;
char **paths = NULL;
if (!ns || !strlen(current))
bail("ns paths are empty");
/*
* We have to open the file descriptors first, since after
* we join the mnt namespace we might no longer be able to
* access the paths.
*/
do {
int fd;
/* Resize fds. */
num++;
fds = realloc(fds, num * sizeof(int));
paths = realloc(paths, num * sizeof(char *));
fd = open(ns, O_RDONLY);
if (fd < 0)
bail("failed to open %s", ns);
fds[num - 1] = fd;
paths[num - 1] = ns;
} while ((ns = strtok_r(NULL, ",", &saveptr)) != NULL);
for (i = 0; i < num; i++) {
int fd = fds[i];
char *path = paths[i];
if (setns(fd, 0) < 0)
bail("failed to setns to %s", path);
close(fd);
}
free(fds);
free(paths);
break;
}
case UIDMAP_ATTR:
config->uidmap = current;
config->uidmap_len = payload_len;
break;
case GIDMAP_ATTR:
config->gidmap = current;
config->gidmap_len = payload_len;
break;
case SETGROUP_ATTR:
config->is_setgroup = readint8(current);
break;
default:
bail("unknown netlink message type %d", nlattr->nla_type);
}
current += NLA_ALIGN(payload_len);
}
}
void nl_free(struct nlconfig_t *config)
{
free(config->data);
}
void nsexec(void)
{
int pipenum;
jmp_buf env;
int syncpipe[2];
struct nlconfig_t config = {0};
/*
* If we don't have an init pipe, just return to the go routine.
* We'll only get an init pipe for start or exec.
*/
pipenum = initpipe();
if (pipenum == -1)
return;
/* Parse all of the netlink configuration. */
nl_parse(pipenum, &config);
/* clone(2) flags are mandatory. */
if (config.cloneflags == -1)
bail("missing clone_flags");
/* Pipe so we can tell the child when we've finished setting up. */
if (pipe(syncpipe) < 0)
bail("failed to setup sync pipe between parent and child");
/* Set up the jump point. */
if (setjmp(env) == JUMP_VAL) {
/*
* We're inside the child now, having jumped from the
* start_child() code after forking in the parent.
*/
uint8_t s = 0;
int consolefd = config.consolefd;
/* Close the writing side of pipe. */
close(syncpipe[1]);
/* Sync with parent. */
if (read(syncpipe[0], &s, sizeof(s)) != sizeof(s) || s != SYNC_VAL)
bail("failed to read sync byte from parent");
if (setsid() < 0)
bail("setsid failed");
if (setuid(0) < 0)
bail("setuid failed");
if (setgid(0) < 0)
bail("setgid failed");
if (setgroups(0, NULL) < 0)
bail("setgroups failed");
if (consolefd != -1) {
if (ioctl(consolefd, TIOCSCTTY, 0) < 0)
bail("ioctl TIOCSCTTY failed");
if (dup3(consolefd, STDIN_FILENO, 0) != STDIN_FILENO)
bail("failed to dup stdin");
if (dup3(consolefd, STDOUT_FILENO, 0) != STDOUT_FILENO)
bail("failed to dup stdout");
if (dup3(consolefd, STDERR_FILENO, 0) != STDERR_FILENO)
bail("failed to dup stderr");
}
/* Free netlink data. */
nl_free(&config);
/* Finish executing, let the Go runtime take over. */
return;
}
/* Run the parent code. */
start_child(pipenum, &env, syncpipe, &config);
/* Should never be reached. */
bail("should never be reached");
}