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// SPDX-License-Identifier: GPL-2.0
/*
* A layer of an overlay is a private clone of the mount it was given and
* belongs to no mount namespace. fanotify hands out descriptors on it. An
* automount triggered through one has no namespace to go into: the open has
* to fail, not oops with namespace_sem held.
*/
#define _GNU_SOURCE
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <linux/magic.h>
#include <sys/fanotify.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/vfs.h>
#include "../../kselftest_harness.h"
#define DIR_LEN 64
#define PATH_LEN 192
static bool have_fs(const char *name)
{
char line[128];
bool found = false;
FILE *f;
f = fopen("/proc/filesystems", "re");
if (!f)
return false;
while (fgets(line, sizeof(line), f)) {
char *nl = strchr(line, '\n');
char *tab = strchr(line, '\t');
if (nl)
*nl = 0;
if (tab && !strcmp(tab + 1, name))
found = true;
}
fclose(f);
return found;
}
static int mnt_id_of(int fd)
{
char path[64], buf[4096], *p;
ssize_t n;
int info;
snprintf(path, sizeof(path), "/proc/self/fdinfo/%d", fd);
info = open(path, O_RDONLY | O_CLOEXEC);
if (info < 0)
return -1;
n = read(info, buf, sizeof(buf) - 1);
close(info);
if (n <= 0)
return -1;
buf[n] = 0;
p = strstr(buf, "mnt_id:");
return p ? atoi(p + strlen("mnt_id:")) : -1;
}
static bool on_debugfs(int fd)
{
struct statfs sf;
return !fstatfs(fd, &sf) && sf.f_type == DEBUGFS_MAGIC;
}
FIXTURE(layer) {
char base[DIR_LEN];
int fan;
int evfd; /* on the layer clone of the lower debugfs */
};
FIXTURE_SETUP(layer)
{
char lower[PATH_LEN], other[PATH_LEN], ovl[PATH_LEN], opts[2 * PATH_LEN + 16];
struct fanotify_event_metadata *ev;
struct pollfd pfd;
char buf[4096];
int lfd, lower_id;
ssize_t n;
DIR *d;
self->fan = -1;
self->evfd = -1;
if (geteuid())
SKIP(return, "test requires root");
if (!have_fs("debugfs") || !have_fs("tracefs"))
SKIP(return, "test requires debugfs with the tracefs automount");
if (!have_fs("overlay"))
SKIP(return, "test requires overlayfs");
snprintf(self->base, sizeof(self->base), "/tmp/layer.XXXXXX");
ASSERT_NE(mkdtemp(self->base), NULL);
ASSERT_EQ(unshare(CLONE_NEWNS), 0);
ASSERT_EQ(mount("", "/", NULL, MS_REC | MS_PRIVATE, NULL), 0);
ASSERT_EQ(mount("tmpfs", self->base, "tmpfs", 0, "mode=0755"), 0);
snprintf(lower, sizeof(lower), "%s/lower", self->base);
snprintf(other, sizeof(other), "%s/other", self->base);
snprintf(ovl, sizeof(ovl), "%s/ovl", self->base);
ASSERT_EQ(mkdir(lower, 0755), 0);
ASSERT_EQ(mkdir(other, 0755), 0);
ASSERT_EQ(mkdir(ovl, 0755), 0);
ASSERT_EQ(mount("debugfs", lower, "debugfs", 0, NULL), 0);
snprintf(opts, sizeof(opts), "lowerdir=%s:%s", lower, other);
ASSERT_EQ(mount("overlay", ovl, "overlay", MS_RDONLY, opts), 0);
self->fan = fanotify_init(FAN_CLASS_NOTIF | FAN_NONBLOCK | FAN_CLOEXEC,
O_RDONLY | O_CLOEXEC);
ASSERT_GE(self->fan, 0);
ASSERT_EQ(fanotify_mark(self->fan, FAN_MARK_ADD | FAN_MARK_FILESYSTEM,
FAN_OPEN | FAN_ONDIR, AT_FDCWD, lower), 0);
lfd = open(lower, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
ASSERT_GE(lfd, 0);
lower_id = mnt_id_of(lfd);
close(lfd);
/* the overlay opens its lower directory through the layer clone */
d = opendir(ovl);
ASSERT_NE(d, NULL);
closedir(d);
pfd.fd = self->fan;
pfd.events = POLLIN;
ASSERT_EQ(poll(&pfd, 1, 5000), 1);
n = read(self->fan, buf, sizeof(buf));
ASSERT_GT(n, 0);
for (ev = (void *)buf; FAN_EVENT_OK(ev, n); ev = FAN_EVENT_NEXT(ev, n)) {
if (ev->fd < 0)
continue;
if (self->evfd < 0 && on_debugfs(ev->fd) &&
mnt_id_of(ev->fd) != lower_id)
self->evfd = ev->fd;
else
close(ev->fd);
}
ASSERT_GE(self->evfd, 0)
TH_LOG("no event on the layer clone");
}
FIXTURE_TEARDOWN(layer)
{
if (self->evfd >= 0)
close(self->evfd);
if (self->fan >= 0)
close(self->fan);
umount2(self->base, MNT_DETACH);
rmdir(self->base);
}
TEST_F(layer, automount_below_the_clone_is_refused)
{
struct stat st;
int fd;
/* the automount point is there */
ASSERT_EQ(fstatat(self->evfd, "tracing", &st, AT_NO_AUTOMOUNT), 0);
/* the clone is in no namespace, so the automount has nowhere to go */
fd = openat(self->evfd, "tracing", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
EXPECT_LT(fd, 0);
EXPECT_EQ(errno, EINVAL);
if (fd >= 0)
close(fd);
}
TEST_HARNESS_MAIN
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