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/* $OpenBSD: explicit_bzero.c,v 1.2 2014/07/09 14:26:59 bcook Exp $ */
/*
* Copyright (c) 2014 Google Inc.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <assert.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>
#define ASSERT_EQ(a, b) assert((a) == (b))
#define ASSERT_NE(a, b) assert((a) != (b))
#define ASSERT_GE(a, b) assert((a) >= (b))
static void
call_on_stack(void (*fn)(int), void *stack, size_t stacklen)
{
/*
* This is a bit more complicated than strictly necessary, but
* it ensures we don't have any flaky test failures due to
* inherited signal masks/actions/etc.
*
* On systems where SA_ONSTACK is not supported, this could
* alternatively be implemented using makecontext() or
* pthread_attr_setstack().
*/
const struct sigaction sigact = {
.sa_handler = fn,
.sa_flags = SA_ONSTACK,
};
const stack_t sigstk = {
.ss_sp = stack,
.ss_size = stacklen,
};
struct sigaction oldsigact;
stack_t oldsigstk;
sigset_t sigset, oldsigset;
/* First, block all signals. */
ASSERT_EQ(0, sigemptyset(&sigset));
ASSERT_EQ(0, sigfillset(&sigset));
ASSERT_EQ(0, sigprocmask(SIG_BLOCK, &sigset, &oldsigset));
/* Next setup the signal stack and handler for SIGUSR1. */
ASSERT_EQ(0, sigaltstack(&sigstk, &oldsigstk));
ASSERT_EQ(0, sigaction(SIGUSR1, &sigact, &oldsigact));
/* Raise SIGUSR1 and momentarily unblock it to run the handler. */
ASSERT_EQ(0, raise(SIGUSR1));
ASSERT_EQ(0, sigdelset(&sigset, SIGUSR1));
ASSERT_EQ(-1, sigsuspend(&sigset));
ASSERT_EQ(EINTR, errno);
/* Restore the original signal action, stack, and mask. */
ASSERT_EQ(0, sigaction(SIGUSR1, &oldsigact, NULL));
if (oldsigstk.ss_flags & SA_ONSTACK)
ASSERT_EQ(0, sigaltstack(&oldsigstk, NULL));
ASSERT_EQ(0, sigprocmask(SIG_SETMASK, &oldsigset, NULL));
}
/* 128 bits of random data. */
static const char secret[16] = {
0xa0, 0x6c, 0x0c, 0x81, 0xba, 0xd8, 0x5b, 0x0c,
0xb0, 0xd6, 0xd4, 0xe3, 0xeb, 0x52, 0x5f, 0x96,
};
enum {
SECRETCOUNT = 16,
SECRETBYTES = SECRETCOUNT * sizeof(secret)
};
static void
populate_secret(char *buf, size_t len)
{
int i, fds[2];
ASSERT_EQ(0, pipe(fds));
for (i = 0; i < SECRETCOUNT; i++)
ASSERT_EQ(sizeof(secret), write(fds[1], secret, sizeof(secret)));
ASSERT_EQ(0, close(fds[1]));
ASSERT_EQ(len, read(fds[0], buf, len));
ASSERT_EQ(0, close(fds[0]));
}
static void
test_without_bzero(int signo)
{
char buf[SECRETBYTES];
populate_secret(buf, sizeof(buf));
}
static void
test_with_bzero(int signo)
{
char buf[SECRETBYTES];
populate_secret(buf, sizeof(buf));
explicit_bzero(buf, sizeof(buf));
}
static char altstack[SIGSTKSZ];
int
main()
{
/*
* First, test that if we *don't* call explicit_bzero, that we
* *are* able to find the secret data on the stack. This
* sanity checks that call_on_stack() and populare_secret()
* work as intended.
*/
memset(altstack, 0, sizeof(altstack));
call_on_stack(test_without_bzero, altstack, sizeof(altstack));
ASSERT_NE(NULL, memmem(altstack, sizeof(altstack), secret, sizeof(secret)));
/*
* Now test with a call to explicit_bzero() and check that we
* *don't* find the secret data.
*/
memset(altstack, 0, sizeof(altstack));
call_on_stack(test_with_bzero, altstack, sizeof(altstack));
ASSERT_EQ(NULL, memmem(altstack, sizeof(altstack), secret, sizeof(secret)));
return (0);
}
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