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// SPDX-License-Identifier: GPL-2.0
/*
* Asserting interpreter for the transparent binfmt_misc mode. It runs in
* place of the dispatched binary and verifies the identity the kernel
* constructed: the aux vector contract, the exe link, argv, cmdline, comm
* and the write denial on the binary. BINFMT_TEST_BINARY names the binary;
* the harness execs it with the arguments "argone argtwo". Prints
* TRANSPARENT_OK and exits 0 when every check holds.
*/
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/auxv.h>
#include <sys/stat.h>
#include <unistd.h>
#include "binfmt_misc_common.h"
#include "kselftest.h"
#ifndef AT_FLAGS_TRANSPARENT_INTERP
#define AT_FLAGS_TRANSPARENT_INTERP (1 << 1)
#endif
static int fail;
static void ok(int cond, const char *what)
{
if (!cond) {
fprintf(stderr, "TRANSPARENT_FAIL: %s (errno %d)\n", what, errno);
fail = 1;
}
}
int main(int argc, char **argv)
{
const char *binary = getenv("BINFMT_TEST_BINARY");
const char *argv0 = getenv("BINFMT_TEST_ARGV0");
char expect[PATH_MAX + 32], buf[PATH_MAX];
unsigned long execfd;
struct stat stb, stfd;
const char *want[3];
const char *base;
size_t expect_len, i;
int fd, have_stb, have_stfd;
ssize_t n;
if (!binary) {
fprintf(stderr, "TRANSPARENT_FAIL: BINFMT_TEST_BINARY unset\n");
return 1;
}
/* Distinct from the binary path, so a classic argv splice is caught. */
want[0] = argv0 ? argv0 : binary;
want[1] = PAYLOAD_ARG1;
want[2] = PAYLOAD_ARG2;
/* The aux vector announces the transparent contract. */
ok(getauxval(AT_FLAGS) & AT_FLAGS_TRANSPARENT_INTERP,
"AT_FLAGS lacks AT_FLAGS_TRANSPARENT_INTERP");
/* AT_EXECFD refers to the very file that was executed. */
execfd = getauxval(AT_EXECFD);
ok(execfd > 2, "no AT_EXECFD");
have_stb = !stat(binary, &stb);
ok(have_stb, "cannot stat the binary");
have_stfd = !fstat((int)execfd, &stfd);
ok(have_stfd, "cannot fstat AT_EXECFD");
ok(have_stb && have_stfd && stb.st_dev == stfd.st_dev &&
stb.st_ino == stfd.st_ino, "AT_EXECFD is not the binary");
/* The exe link names the binary, not this interpreter. */
ok(exe_is(binary), "/proc/self/exe is not the binary");
/* argv arrived unspliced. */
ok(argc == (int)ARRAY_SIZE(want), "argv was rewritten");
for (i = 0; i < ARRAY_SIZE(want) && i < (size_t)argc; i++)
ok(!strcmp(argv[i], want[i]), "argv was rewritten");
/* And so did the kernel's copy of it: the same strings, NUL separated. */
for (i = 0, expect_len = 0; i < ARRAY_SIZE(want); i++) {
size_t len = strlen(want[i]) + 1;
if (expect_len + len > sizeof(expect)) {
ok(0, "argv does not fit the expectation buffer");
break;
}
memcpy(expect + expect_len, want[i], len);
expect_len += len;
}
fd = open("/proc/self/cmdline", O_RDONLY);
n = fd >= 0 ? read(fd, buf, sizeof(buf)) : -1;
if (fd >= 0)
close(fd);
ok(n == (ssize_t)expect_len && !memcmp(buf, expect, expect_len),
"/proc/self/cmdline was rewritten");
/* comm is the binary's basename. */
base = strrchr(binary, '/');
base = base ? base + 1 : binary;
ok(comm_is(base), "comm is not the binary's basename");
/* The binary is write-denied while it runs, like a direct exec. */
ok(write_denied(binary), "binary is writable while running");
ok(write_denied("/proc/self/exe"), "exe link is writable while running");
if (!fail)
printf("TRANSPARENT_OK\n");
return fail;
}
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