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// SPDX-License-Identifier: AGPL-3.0-or-later
/* PASST - Plug A Simple Socket Transport
* for qemu/UNIX domain socket mode
*
* PASTA - Pack A Subtle Tap Abstraction
* for network namespace/tap device mode
*
* isolation.c - Self isolation helpers
*
* Copyright Red Hat
* Author: Stefano Brivio <sbrivio@redhat.com>
* Author: David Gibson <david@gibson.dropbear.id.au>
*/
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <inttypes.h>
#include <limits.h>
#include <pwd.h>
#include <sched.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/mount.h>
#include <sys/prctl.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <linux/audit.h>
#include <linux/capability.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
#include "util.h"
#include "seccomp.h"
#include "passt.h"
#include "log.h"
#include "isolation.h"
/**
* drop_caps() - Drop capabilities we might have except for CAP_NET_BIND_SERVICE
*/
void drop_caps(void)
{
int i;
for (i = 0; i < 64; i++) {
if (i == CAP_NET_BIND_SERVICE)
continue;
prctl(PR_CAPBSET_DROP, i, 0, 0, 0);
}
}
/**
* isolate_user() - Switch to final UID/GID and move into userns
* @uid: User ID to run as (in original userns)
* @gid: Group ID to run as (in original userns)
* @use_userns: Whether to join or create a userns
* @userns: userns path to enter, may be empty
*/
void isolate_user(uid_t uid, gid_t gid, bool use_userns, const char *userns)
{
char nsmap[BUFSIZ];
/* First set our UID & GID in the original namespace */
if (setgroups(0, NULL)) {
/* If we don't have CAP_SETGID, this will EPERM */
if (errno != EPERM) {
err("Can't drop supplementary groups: %s",
strerror(errno));
exit(EXIT_FAILURE);
}
}
if (setgid(gid) != 0) {
err("Can't set GID to %u: %s", gid, strerror(errno));
exit(EXIT_FAILURE);
}
if (setuid(uid) != 0) {
err("Can't set UID to %u: %s", uid, strerror(errno));
exit(EXIT_FAILURE);
}
/* If we're told not to use a userns, nothing more to do */
if (!use_userns)
return;
/* Otherwise, if given a userns, join it */
if (*userns) {
int ufd;
ufd = open(userns, O_RDONLY | O_CLOEXEC);
if (ufd < 0) {
err("Couldn't open user namespace %s: %s",
userns, strerror(errno));
exit(EXIT_FAILURE);
}
if (setns(ufd, CLONE_NEWUSER) != 0) {
err("Couldn't enter user namespace %s: %s",
userns, strerror(errno));
exit(EXIT_FAILURE);
}
close(ufd);
return;
}
/* Otherwise, create our own userns */
if (unshare(CLONE_NEWUSER) != 0) {
err("Couldn't create user namespace: %s", strerror(errno));
exit(EXIT_FAILURE);
}
/* Configure user and group mappings */
snprintf(nsmap, BUFSIZ, "0 %u 1", uid);
FWRITE("/proc/self/uid_map", nsmap, "Cannot set uid_map in namespace");
FWRITE("/proc/self/setgroups", "deny",
"Cannot write to setgroups in namespace");
snprintf(nsmap, BUFSIZ, "0 %u 1", gid);
FWRITE("/proc/self/gid_map", nsmap, "Cannot set gid_map in namespace");
}
/**
* sandbox() - Unshare IPC, mount, PID, UTS, and user namespaces, "unmount" root
*
* Return: negative error code on failure, zero on success
*/
int sandbox(struct ctx *c)
{
int flags = CLONE_NEWIPC | CLONE_NEWNS | CLONE_NEWUTS;
/* If we run in foreground, we have no chance to actually move to a new
* PID namespace. For passt, use CLONE_NEWPID anyway, in case somebody
* ever gets around seccomp profiles -- there's no harm in passing it.
*/
if (!c->foreground || c->mode == MODE_PASST)
flags |= CLONE_NEWPID;
if (unshare(flags)) {
perror("unshare");
return -errno;
}
if (mount("", "/", "", MS_UNBINDABLE | MS_REC, NULL)) {
perror("mount /");
return -errno;
}
if (mount("", TMPDIR, "tmpfs",
MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RDONLY,
"nr_inodes=2,nr_blocks=0")) {
perror("mount tmpfs");
return -errno;
}
if (chdir(TMPDIR)) {
perror("chdir");
return -errno;
}
if (syscall(SYS_pivot_root, ".", ".")) {
perror("pivot_root");
return -errno;
}
if (umount2(".", MNT_DETACH | UMOUNT_NOFOLLOW)) {
perror("umount2");
return -errno;
}
drop_caps(); /* Relative to the new user namespace this time. */
return 0;
}
/**
* seccomp() - Set up seccomp filters depending on mode, won't return on failure
* @c: Execution context
*/
void seccomp(const struct ctx *c)
{
struct sock_fprog prog;
if (c->mode == MODE_PASST) {
prog.len = (unsigned short)ARRAY_SIZE(filter_passt);
prog.filter = filter_passt;
} else {
prog.len = (unsigned short)ARRAY_SIZE(filter_pasta);
prog.filter = filter_pasta;
}
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) ||
prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
perror("prctl");
exit(EXIT_FAILURE);
}
}
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