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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Author: Aleksa Sarai <cyphar@cyphar.com>
* Copyright (C) 2018-2019 SUSE LLC.
*/
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <sched.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <syscall.h>
#include <limits.h>
#include <unistd.h>
#include "../kselftest.h"
#include "helpers.h"
/* Construct a test directory with the following structure:
*
* root/
* |-- a/
* | `-- c/
* `-- b/
*/
int setup_testdir(void)
{
int dfd;
char dirname[] = "/tmp/ksft-openat2-rename-attack.XXXXXX";
/* Make the top-level directory. */
if (!mkdtemp(dirname))
ksft_exit_fail_msg("setup_testdir: failed to create tmpdir\n");
dfd = open(dirname, O_PATH | O_DIRECTORY);
if (dfd < 0)
ksft_exit_fail_msg("setup_testdir: failed to open tmpdir\n");
E_mkdirat(dfd, "a", 0755);
E_mkdirat(dfd, "b", 0755);
E_mkdirat(dfd, "a/c", 0755);
return dfd;
}
/* Swap @dirfd/@a and @dirfd/@b constantly. Parent must kill this process. */
pid_t spawn_attack(int dirfd, char *a, char *b)
{
pid_t child = fork();
if (child != 0)
return child;
/* If the parent (the test process) dies, kill ourselves too. */
E_prctl(PR_SET_PDEATHSIG, SIGKILL);
/* Swap @a and @b. */
for (;;)
renameat2(dirfd, a, dirfd, b, RENAME_EXCHANGE);
exit(1);
}
#define NUM_RENAME_TESTS 2
#define ROUNDS 400000
const char *flagname(int resolve)
{
switch (resolve) {
case RESOLVE_IN_ROOT:
return "RESOLVE_IN_ROOT";
case RESOLVE_BENEATH:
return "RESOLVE_BENEATH";
}
return "(unknown)";
}
void test_rename_attack(int resolve)
{
int dfd, afd;
pid_t child;
void (*resultfn)(const char *msg, ...) = ksft_test_result_pass;
int escapes = 0, other_errs = 0, exdevs = 0, eagains = 0, successes = 0;
struct open_how how = {
.flags = O_PATH,
.resolve = resolve,
};
if (!openat2_supported) {
how.resolve = 0;
ksft_print_msg("openat2(2) unsupported -- using openat(2) instead\n");
}
dfd = setup_testdir();
afd = openat(dfd, "a", O_PATH);
if (afd < 0)
ksft_exit_fail_msg("test_rename_attack: failed to open 'a'\n");
child = spawn_attack(dfd, "a/c", "b");
for (int i = 0; i < ROUNDS; i++) {
int fd;
char *victim_path = "c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../..";
if (openat2_supported)
fd = sys_openat2(afd, victim_path, &how);
else
fd = sys_openat(afd, victim_path, &how);
if (fd < 0) {
if (fd == -EAGAIN)
eagains++;
else if (fd == -EXDEV)
exdevs++;
else if (fd == -ENOENT)
escapes++; /* escaped outside and got ENOENT... */
else
other_errs++; /* unexpected error */
} else {
if (fdequal(fd, afd, NULL))
successes++;
else
escapes++; /* we got an unexpected fd */
}
close(fd);
}
if (escapes > 0)
resultfn = ksft_test_result_fail;
ksft_print_msg("non-escapes: EAGAIN=%d EXDEV=%d E<other>=%d success=%d\n",
eagains, exdevs, other_errs, successes);
resultfn("rename attack with %s (%d runs, got %d escapes)\n",
flagname(resolve), ROUNDS, escapes);
/* Should be killed anyway, but might as well make sure. */
E_kill(child, SIGKILL);
}
#define NUM_TESTS NUM_RENAME_TESTS
int main(int argc, char **argv)
{
ksft_print_header();
ksft_set_plan(NUM_TESTS);
test_rename_attack(RESOLVE_BENEATH);
test_rename_attack(RESOLVE_IN_ROOT);
if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0)
ksft_exit_fail();
else
ksft_exit_pass();
}
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