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// SPDX-License-Identifier: GPL-2.0
/*
* An unbindable mount stays unbindable in a cloned mount namespace.
*/
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/wait.h>
#include <unistd.h>
#include "../../kselftest_harness.h"
#ifndef OPEN_TREE_CLONE
#define OPEN_TREE_CLONE 1
#endif
#ifndef OPEN_TREE_CLOEXEC
#define OPEN_TREE_CLOEXEC O_CLOEXEC
#endif
static int sys_open_tree(int dfd, const char *filename, unsigned int flags)
{
return syscall(__NR_open_tree, dfd, filename, flags);
}
/* Child exit codes. */
enum {
CHILD_OK, /* the operation failed with EINVAL as it must */
CHILD_ALLOWED, /* the operation succeeded: the flag was lost */
CHILD_UNSHARE, /* unshare(CLONE_NEWNS) failed */
CHILD_ERRNO, /* the operation failed with some other errno */
CHILD_MOUNTINFO, /* the mount was not found in mountinfo */
};
FIXTURE(mntns_unbindable)
{
char base[64];
char src[80];
char dst[80];
bool mounted;
};
FIXTURE_SETUP(mntns_unbindable)
{
self->mounted = false;
if (geteuid() != 0)
SKIP(return, "test requires CAP_SYS_ADMIN");
ASSERT_EQ(unshare(CLONE_NEWNS), 0);
ASSERT_EQ(mount("", "/", NULL, MS_REC | MS_PRIVATE, NULL), 0);
snprintf(self->base, sizeof(self->base), "/tmp/mntns_unbindable.XXXXXX");
ASSERT_NE(mkdtemp(self->base), NULL);
ASSERT_EQ(mount("tmpfs", self->base, "tmpfs", 0, NULL), 0);
self->mounted = true;
snprintf(self->src, sizeof(self->src), "%s/src", self->base);
snprintf(self->dst, sizeof(self->dst), "%s/dst", self->base);
ASSERT_EQ(mkdir(self->src, 0755), 0);
ASSERT_EQ(mkdir(self->dst, 0755), 0);
ASSERT_EQ(mount("tmpfs", self->src, "tmpfs", 0, NULL), 0);
ASSERT_EQ(mount(NULL, self->src, NULL, MS_UNBINDABLE, NULL), 0);
}
FIXTURE_TEARDOWN(mntns_unbindable)
{
if (self->mounted)
umount2(self->base, MNT_DETACH);
rmdir(self->base);
}
static int classify(int ret, int err)
{
if (ret >= 0)
return CHILD_ALLOWED;
return err == EINVAL ? CHILD_OK : CHILD_ERRNO;
}
/* Is the mount on @mountpoint marked unbindable in /proc/self/mountinfo? */
static int mountinfo_unbindable(const char *mountpoint)
{
char line[4096];
FILE *f;
int ret = CHILD_MOUNTINFO;
f = fopen("/proc/self/mountinfo", "re");
if (!f)
return CHILD_ERRNO;
while (fgets(line, sizeof(line), f)) {
char *fields[6], *p = line, *opt;
int i;
for (i = 0; i < 6; i++) {
fields[i] = strsep(&p, " ");
if (!fields[i])
break;
}
if (i < 6 || strcmp(fields[4], mountpoint))
continue;
/* the optional fields, up to the "-" separator */
ret = CHILD_ALLOWED;
while ((opt = strsep(&p, " ")) && strcmp(opt, "-")) {
if (!strcmp(opt, "unbindable"))
ret = CHILD_OK;
}
break;
}
fclose(f);
return ret;
}
static int run_in_child(int (*fn)(const char *src, const char *dst),
const char *src, const char *dst)
{
int status;
pid_t pid;
pid = fork();
if (pid < 0)
return -1;
if (pid == 0)
_exit(fn(src, dst));
if (waitpid(pid, &status, 0) != pid || !WIFEXITED(status))
return -1;
return WEXITSTATUS(status);
}
static int bind_after_clone(const char *src, const char *dst)
{
int ret;
if (unshare(CLONE_NEWNS))
return CHILD_UNSHARE;
ret = mount(src, dst, NULL, MS_BIND, NULL);
return classify(ret, errno);
}
static int rbind_after_clone(const char *src, const char *dst)
{
int ret;
if (unshare(CLONE_NEWNS))
return CHILD_UNSHARE;
ret = mount(src, dst, NULL, MS_BIND | MS_REC, NULL);
return classify(ret, errno);
}
static int open_tree_after_clone(const char *src, const char *dst)
{
int ret;
if (unshare(CLONE_NEWNS))
return CHILD_UNSHARE;
ret = sys_open_tree(AT_FDCWD, src, OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
return classify(ret, errno);
}
static int mountinfo_after_clone(const char *src, const char *dst)
{
if (unshare(CLONE_NEWNS))
return CHILD_UNSHARE;
return mountinfo_unbindable(src);
}
static int bind_after_two_clones(const char *src, const char *dst)
{
int ret;
if (unshare(CLONE_NEWNS))
return CHILD_UNSHARE;
if (unshare(CLONE_NEWNS))
return CHILD_UNSHARE;
ret = mount(src, dst, NULL, MS_BIND, NULL);
return classify(ret, errno);
}
/* The namespace the mount was made unbindable in. */
TEST_F(mntns_unbindable, refuses_bind)
{
int ret = mount(self->src, self->dst, NULL, MS_BIND, NULL);
ASSERT_EQ(classify(ret, errno), CHILD_OK);
ASSERT_EQ(mountinfo_unbindable(self->src), CHILD_OK);
}
/* A copy of the namespace must not turn the mount bindable. */
TEST_F(mntns_unbindable, refuses_bind_after_clone)
{
ASSERT_EQ(run_in_child(bind_after_clone, self->src, self->dst), CHILD_OK)
TH_LOG("bind of an unbindable mount allowed in a copied mount namespace");
}
TEST_F(mntns_unbindable, refuses_rbind_after_clone)
{
ASSERT_EQ(run_in_child(rbind_after_clone, self->src, self->dst), CHILD_OK)
TH_LOG("rbind of an unbindable mount allowed in a copied mount namespace");
}
TEST_F(mntns_unbindable, refuses_open_tree_after_clone)
{
ASSERT_EQ(run_in_child(open_tree_after_clone, self->src, self->dst), CHILD_OK)
TH_LOG("OPEN_TREE_CLONE of an unbindable mount allowed in a copied mount namespace");
}
TEST_F(mntns_unbindable, mountinfo_after_clone)
{
ASSERT_EQ(run_in_child(mountinfo_after_clone, self->src, self->dst), CHILD_OK)
TH_LOG("mountinfo does not show the mount as unbindable in a copied mount namespace");
}
TEST_F(mntns_unbindable, refuses_bind_after_two_clones)
{
ASSERT_EQ(run_in_child(bind_after_two_clones, self->src, self->dst), CHILD_OK)
TH_LOG("bind of an unbindable mount allowed two mount namespace copies down");
}
TEST_HARNESS_MAIN
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