Tor 0.4.9.0-alpha-dev
crypto_util.c
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1/* Copyright (c) 2001, Matej Pfajfar.
2 * Copyright (c) 2001-2004, Roger Dingledine.
3 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
4 * Copyright (c) 2007-2021, The Tor Project, Inc. */
5/* See LICENSE for licensing information */
6
7/**
8 * \file crypto_util.c
9 *
10 * \brief Common cryptographic utilities.
11 **/
12
15
16#include <string.h>
17
18#ifdef _WIN32
19#include <winsock2.h>
20#include <windows.h>
21#include <wincrypt.h>
22#endif /* defined(_WIN32) */
23
24#include <stdlib.h>
25
26#ifdef ENABLE_OPENSSL
27DISABLE_GCC_WARNING("-Wredundant-decls")
28#include <openssl/err.h>
29#include <openssl/crypto.h>
30ENABLE_GCC_WARNING("-Wredundant-decls")
31#endif /* defined(ENABLE_OPENSSL) */
32
33#include "lib/log/log.h"
34#include "lib/log/util_bug.h"
35
36/**
37 * Destroy the <b>sz</b> bytes of data stored at <b>mem</b>, setting them to
38 * the value <b>byte</b>.
39 * If <b>mem</b> is NULL or <b>sz</b> is zero, nothing happens.
40 *
41 * This function is preferable to memset, since many compilers will happily
42 * optimize out memset() when they can convince themselves that the data being
43 * cleared will never be read.
44 *
45 * Right now, our convention is to use this function when we are wiping data
46 * that's about to become inaccessible, such as stack buffers that are about
47 * to go out of scope or structures that are about to get freed. (In
48 * practice, it appears that the compilers we're currently using will optimize
49 * out the memset()s for stack-allocated buffers, but not those for
50 * about-to-be-freed structures. That could change, though, so we're being
51 * wary.) If there are live reads for the data, then you can just use
52 * memset().
53 */
54void
55memwipe(void *mem, uint8_t byte, size_t sz)
56{
57 if (sz == 0) {
58 return;
59 }
60 /* If sz is nonzero, then mem must not be NULL. */
61 tor_assert(mem != NULL);
62
63 /* Data this large is likely to be an underflow. */
65
66 /* Because whole-program-optimization exists, we may not be able to just
67 * have this function call "memset". A smart compiler could inline it, then
68 * eliminate dead memsets, and declare itself to be clever. */
69
70#if defined(SecureZeroMemory) || defined(HAVE_SECUREZEROMEMORY)
71 /* Here's what you do on windows. */
72 SecureZeroMemory(mem,sz);
73#elif defined(HAVE_RTLSECUREZEROMEMORY)
74 RtlSecureZeroMemory(mem,sz);
75#elif defined(HAVE_EXPLICIT_BZERO)
76 /* The BSDs provide this. */
77 explicit_bzero(mem, sz);
78#elif defined(HAVE_MEMSET_S)
79 /* This is in the C99 standard. */
80 memset_s(mem, sz, 0, sz);
81#elif defined(ENABLE_OPENSSL)
82 /* This is a slow and ugly function from OpenSSL that fills 'mem' with junk
83 * based on the pointer value, then uses that junk to update a global
84 * variable. It's an elaborate ruse to trick the compiler into not
85 * optimizing out the "wipe this memory" code. Read it if you like zany
86 * programming tricks! In later versions of Tor, we should look for better
87 * not-optimized-out memory wiping stuff...
88 *
89 * ...or maybe not. In practice, there are pure-asm implementations of
90 * OPENSSL_cleanse() on most platforms, which ought to do the job.
91 **/
92
93 OPENSSL_cleanse(mem, sz);
94#else
95 memset(mem, 0, sz);
96 asm volatile("" ::: "memory");
97#endif /* defined(SecureZeroMemory) || defined(HAVE_SECUREZEROMEMORY) || ... */
98
99 /* Just in case some caller of memwipe() is relying on getting a buffer
100 * filled with a particular value, fill the buffer.
101 *
102 * If this function gets inlined, this memset might get eliminated, but
103 * that's okay: We only care about this particular memset in the case where
104 * the caller should have been using memset(), and the memset() wouldn't get
105 * eliminated. In other words, this is here so that we won't break anything
106 * if somebody accidentally calls memwipe() instead of memset().
107 **/
108 memset(mem, byte, sz);
109}
110
111/**
112 * Securely all memory in <b>str</b>, then free it.
113 *
114 * As tor_free(), tolerates null pointers.
115 **/
116void
118{
119 if (!str)
120 return;
121 memwipe(str, 0, strlen(str));
122 tor_free_(str);
123}
Utility macros to handle different features and behavior in different compilers.
void tor_str_wipe_and_free_(char *str)
Definition: crypto_util.c:117
void memwipe(void *mem, uint8_t byte, size_t sz)
Definition: crypto_util.c:55
Common functions for cryptographic routines.
Headers for log.c.
void tor_free_(void *mem)
Definition: malloc.c:227
#define SIZE_T_CEILING
Definition: torint.h:126
Macros to manage assertions, fatal and non-fatal.
#define tor_assert(expr)
Definition: util_bug.h:103