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// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <sched.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/vfs.h>
#include <unistd.h>
#ifndef MS_NOSYMFOLLOW
# define MS_NOSYMFOLLOW 256 /* Do not follow symlinks */
#endif
#ifndef ST_NOSYMFOLLOW
# define ST_NOSYMFOLLOW 0x2000 /* Do not follow symlinks */
#endif
#define DATA "/tmp/data"
#define LINK "/tmp/symlink"
#define TMP "/tmp"
static void die(char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vfprintf(stderr, fmt, ap);
va_end(ap);
exit(EXIT_FAILURE);
}
static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt,
va_list ap)
{
ssize_t written;
char buf[4096];
int buf_len;
int fd;
buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
if (buf_len < 0)
die("vsnprintf failed: %s\n", strerror(errno));
if (buf_len >= sizeof(buf))
die("vsnprintf output truncated\n");
fd = open(filename, O_WRONLY);
if (fd < 0) {
if ((errno == ENOENT) && enoent_ok)
return;
die("open of %s failed: %s\n", filename, strerror(errno));
}
written = write(fd, buf, buf_len);
if (written != buf_len) {
if (written >= 0) {
die("short write to %s\n", filename);
} else {
die("write to %s failed: %s\n",
filename, strerror(errno));
}
}
if (close(fd) != 0)
die("close of %s failed: %s\n", filename, strerror(errno));
}
static void maybe_write_file(char *filename, char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vmaybe_write_file(true, filename, fmt, ap);
va_end(ap);
}
static void write_file(char *filename, char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vmaybe_write_file(false, filename, fmt, ap);
va_end(ap);
}
static void create_and_enter_ns(void)
{
uid_t uid = getuid();
gid_t gid = getgid();
if (unshare(CLONE_NEWUSER) != 0)
die("unshare(CLONE_NEWUSER) failed: %s\n", strerror(errno));
maybe_write_file("/proc/self/setgroups", "deny");
write_file("/proc/self/uid_map", "0 %d 1", uid);
write_file("/proc/self/gid_map", "0 %d 1", gid);
if (setgid(0) != 0)
die("setgid(0) failed %s\n", strerror(errno));
if (setuid(0) != 0)
die("setuid(0) failed %s\n", strerror(errno));
if (unshare(CLONE_NEWNS) != 0)
die("unshare(CLONE_NEWNS) failed: %s\n", strerror(errno));
}
static void setup_symlink(void)
{
int data, err;
data = creat(DATA, O_RDWR);
if (data < 0)
die("creat failed: %s\n", strerror(errno));
err = symlink(DATA, LINK);
if (err < 0)
die("symlink failed: %s\n", strerror(errno));
if (close(data) != 0)
die("close of %s failed: %s\n", DATA, strerror(errno));
}
static void test_link_traversal(bool nosymfollow)
{
int link;
link = open(LINK, 0, O_RDWR);
if (nosymfollow) {
if ((link != -1 || errno != ELOOP)) {
die("link traversal unexpected result: %d, %s\n",
link, strerror(errno));
}
} else {
if (link < 0)
die("link traversal failed: %s\n", strerror(errno));
if (close(link) != 0)
die("close of link failed: %s\n", strerror(errno));
}
}
static void test_readlink(void)
{
char buf[4096];
ssize_t ret;
bzero(buf, sizeof(buf));
ret = readlink(LINK, buf, sizeof(buf));
if (ret < 0)
die("readlink failed: %s\n", strerror(errno));
if (strcmp(buf, DATA) != 0)
die("readlink strcmp failed: '%s' '%s'\n", buf, DATA);
}
static void test_realpath(void)
{
char *path = realpath(LINK, NULL);
if (!path)
die("realpath failed: %s\n", strerror(errno));
if (strcmp(path, DATA) != 0)
die("realpath strcmp failed\n");
free(path);
}
static void test_statfs(bool nosymfollow)
{
struct statfs buf;
int ret;
ret = statfs(TMP, &buf);
if (ret)
die("statfs failed: %s\n", strerror(errno));
if (nosymfollow) {
if ((buf.f_flags & ST_NOSYMFOLLOW) == 0)
die("ST_NOSYMFOLLOW not set on %s\n", TMP);
} else {
if ((buf.f_flags & ST_NOSYMFOLLOW) != 0)
die("ST_NOSYMFOLLOW set on %s\n", TMP);
}
}
static void run_tests(bool nosymfollow)
{
test_link_traversal(nosymfollow);
test_readlink();
test_realpath();
test_statfs(nosymfollow);
}
int main(int argc, char **argv)
{
create_and_enter_ns();
if (mount("testing", TMP, "ramfs", 0, NULL) != 0)
die("mount failed: %s\n", strerror(errno));
setup_symlink();
run_tests(false);
if (mount("testing", TMP, "ramfs", MS_REMOUNT|MS_NOSYMFOLLOW, NULL) != 0)
die("remount failed: %s\n", strerror(errno));
run_tests(true);
return EXIT_SUCCESS;
}
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