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// SPDX-License-Identifier: GPL-2.0
/*
* open_tree(OPEN_TREE_NAMESPACE) by a caller that isn't privileged over the
* mount namespace it copies from must not reveal what the mounts below the
* copied mount cover. Without AT_RECURSIVE the copy is refused when there's
* anything mounted below the requested directory. With AT_RECURSIVE
* unbindable mounts are copied as well.
*/
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include "../wrappers.h"
#include "../../kselftest_harness.h"
#ifndef OPEN_TREE_NAMESPACE
#define OPEN_TREE_NAMESPACE (1 << 1)
#endif
#define DIR_LEN 64
#define PATH_LEN 128
/* Child exit codes. */
enum {
CHILD_OK,
CHILD_USERNS, /* could not create the child user namespace */
CHILD_NONREC_ALLOWED, /* the non-recursive copy was not refused */
CHILD_NONREC_ERRNO, /* it was refused with the wrong error */
CHILD_REC_REFUSED, /* the recursive copy failed */
CHILD_SETNS, /* could not enter the new mount namespace */
CHILD_NO_COVER, /* the covering mount is missing in the copy */
CHILD_REVEALED, /* the covered file is visible in the copy */
};
static int write_file(const char *path, const char *s)
{
ssize_t n = -1;
int fd;
fd = open(path, O_WRONLY | O_CLOEXEC);
if (fd >= 0) {
n = write(fd, s, strlen(s));
close(fd);
}
return n == (ssize_t)strlen(s) ? 0 : -1;
}
static int create_file(const char *path, const char *s)
{
ssize_t n = -1;
int fd;
fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
if (fd >= 0) {
n = write(fd, s, strlen(s));
close(fd);
}
return n == (ssize_t)strlen(s) ? 0 : -1;
}
/* Become root in a new user namespace, the uid @uid is mapped to 0. */
static int enter_userns(uid_t uid, gid_t gid)
{
char map[32];
if (unshare(CLONE_NEWUSER))
return -1;
if (write_file("/proc/self/setgroups", "deny") && errno != ENOENT)
return -1;
snprintf(map, sizeof(map), "0 %d 1", uid);
if (write_file("/proc/self/uid_map", map))
return -1;
snprintf(map, sizeof(map), "0 %d 1", gid);
if (write_file("/proc/self/gid_map", map))
return -1;
return setgid(0) || setuid(0) ? -1 : 0;
}
FIXTURE(open_tree_ns_covered) {
char dir[DIR_LEN];
char cover[PATH_LEN];
};
FIXTURE_VARIANT(open_tree_ns_covered) {
int propagation;
};
FIXTURE_VARIANT_ADD(open_tree_ns_covered, private_cover) {
.propagation = MS_PRIVATE,
};
FIXTURE_VARIANT_ADD(open_tree_ns_covered, unbindable_cover) {
.propagation = MS_UNBINDABLE,
};
/*
* Root in a user namespace owns a private mount namespace with a tmpfs
* on @dir and a second tmpfs covering @dir/covered/under.txt.
*/
FIXTURE_SETUP(open_tree_ns_covered)
{
char p[PATH_LEN];
int fd;
snprintf(self->dir, sizeof(self->dir), "/tmp/open_tree_ns_covered.XXXXXX");
ASSERT_NE(mkdtemp(self->dir), NULL);
if (enter_userns(getuid(), getgid()) || unshare(CLONE_NEWNS)) {
rmdir(self->dir);
SKIP(return, "test requires user namespaces");
}
ASSERT_EQ(mount("", "/", NULL, MS_REC | MS_PRIVATE, NULL), 0);
ASSERT_EQ(mount("tmpfs", self->dir, "tmpfs", 0, NULL), 0);
/* the flag has to exist before its rules can be checked */
fd = sys_open_tree(AT_FDCWD, self->dir,
OPEN_TREE_NAMESPACE | OPEN_TREE_CLOEXEC);
if (fd < 0 && (errno == EINVAL || errno == ENOSYS)) {
umount2(self->dir, MNT_DETACH);
rmdir(self->dir);
SKIP(return, "OPEN_TREE_NAMESPACE not supported");
}
ASSERT_GE(fd, 0);
close(fd);
snprintf(self->cover, sizeof(self->cover), "%s/covered", self->dir);
ASSERT_EQ(mkdir(self->cover, 0755), 0);
snprintf(p, sizeof(p), "%s/covered/under.txt", self->dir);
ASSERT_EQ(create_file(p, "hidden"), 0);
ASSERT_EQ(mount("tmpfs", self->cover, "tmpfs", 0, NULL), 0);
ASSERT_EQ(mount(NULL, self->cover, NULL, variant->propagation, NULL), 0);
}
FIXTURE_TEARDOWN(open_tree_ns_covered)
{
umount2(self->dir, MNT_DETACH);
rmdir(self->dir);
}
/* A caller in a new user namespace that doesn't own the mount namespace. */
static int foreign_child(const char *dir)
{
struct stat st;
int fd;
if (enter_userns(0, 0))
return CHILD_USERNS;
fd = sys_open_tree(AT_FDCWD, dir, OPEN_TREE_NAMESPACE | OPEN_TREE_CLOEXEC);
if (fd >= 0)
return CHILD_NONREC_ALLOWED;
if (errno != EINVAL)
return CHILD_NONREC_ERRNO;
fd = sys_open_tree(AT_FDCWD, dir,
OPEN_TREE_NAMESPACE | OPEN_TREE_CLOEXEC | AT_RECURSIVE);
if (fd < 0)
return CHILD_REC_REFUSED;
if (setns(fd, CLONE_NEWNS))
return CHILD_SETNS;
if (stat("/covered", &st))
return CHILD_NO_COVER;
if (!access("/covered/under.txt", F_OK) || errno != ENOENT)
return CHILD_REVEALED;
return CHILD_OK;
}
TEST_F(open_tree_ns_covered, foreign_user_namespace)
{
int status, fd;
pid_t pid;
pid = fork();
ASSERT_GE(pid, 0);
if (pid == 0)
_exit(foreign_child(self->dir));
ASSERT_EQ(waitpid(pid, &status, 0), pid);
ASSERT_TRUE(WIFEXITED(status));
ASSERT_EQ(WEXITSTATUS(status), CHILD_OK);
/* the owner of the mount namespace keeps bind mount semantics */
fd = sys_open_tree(AT_FDCWD, self->dir,
OPEN_TREE_NAMESPACE | OPEN_TREE_CLOEXEC);
ASSERT_GE(fd, 0);
close(fd);
}
TEST_HARNESS_MAIN
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