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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 "helpers.h"
#include "kselftest_harness.h"
#define ROUNDS 400000
/* Swap @dirfd/@a and @dirfd/@b constantly. Parent must kill this process. */
pid_t spawn_attack(struct __test_metadata *_metadata,
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. */
ASSERT_EQ(prctl(PR_SET_PDEATHSIG, SIGKILL), 0);
/* Swap @a and @b. */
for (;;)
renameat2(dirfd, a, dirfd, b, RENAME_EXCHANGE);
exit(1);
}
/*
* Construct a test directory with the following structure:
*
* root/
* |-- a/
* | `-- c/
* `-- b/
*/
FIXTURE(rename_attack) {
int dfd;
int afd;
pid_t child;
};
FIXTURE_SETUP(rename_attack)
{
char dirname[] = "/tmp/ksft-openat2-rename-attack.XXXXXX";
self->dfd = -1;
self->afd = -1;
self->child = 0;
/* Make the top-level directory. */
ASSERT_NE(mkdtemp(dirname), NULL);
self->dfd = open(dirname, O_PATH | O_DIRECTORY);
ASSERT_GE(self->dfd, 0);
ASSERT_EQ(mkdirat(self->dfd, "a", 0755), 0);
ASSERT_EQ(mkdirat(self->dfd, "b", 0755), 0);
ASSERT_EQ(mkdirat(self->dfd, "a/c", 0755), 0);
self->afd = openat(self->dfd, "a", O_PATH);
ASSERT_GE(self->afd, 0);
self->child = spawn_attack(_metadata, self->dfd, "a/c", "b");
ASSERT_GT(self->child, 0);
}
FIXTURE_TEARDOWN(rename_attack)
{
if (self->child > 0)
kill(self->child, SIGKILL);
if (self->afd >= 0)
close(self->afd);
if (self->dfd >= 0)
close(self->dfd);
}
FIXTURE_VARIANT(rename_attack) {
int resolve;
const char *name;
};
FIXTURE_VARIANT_ADD(rename_attack, resolve_beneath) {
.resolve = RESOLVE_BENEATH,
.name = "RESOLVE_BENEATH",
};
FIXTURE_VARIANT_ADD(rename_attack, resolve_in_root) {
.resolve = RESOLVE_IN_ROOT,
.name = "RESOLVE_IN_ROOT",
};
TEST_F_TIMEOUT(rename_attack, test, 120)
{
int escapes = 0, successes = 0, other_errs = 0, exdevs = 0, eagains = 0;
char *victim_path = "c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../../c/../..";
struct open_how how = {
.flags = O_PATH,
.resolve = variant->resolve,
};
if (!openat2_supported) {
how.resolve = 0;
TH_LOG("openat2(2) unsupported -- using openat(2) instead");
}
for (int i = 0; i < ROUNDS; i++) {
int fd;
if (openat2_supported)
fd = sys_openat2(self->afd, victim_path, &how);
else
fd = sys_openat(self->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(_metadata, fd, self->afd, NULL))
successes++;
else
escapes++; /* we got an unexpected fd */
}
if (fd >= 0)
close(fd);
}
TH_LOG("non-escapes: EAGAIN=%d EXDEV=%d E<other>=%d success=%d",
eagains, exdevs, other_errs, successes);
ASSERT_EQ(escapes, 0) {
TH_LOG("rename attack with %s (%d runs, got %d escapes)",
variant->name, ROUNDS, escapes);
}
}
TEST_HARNESS_MAIN
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