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lighttpd1.4/src/mod_secdownload.c

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#include "first.h"
#include "base.h"
#include "log.h"
#include "buffer.h"
#include "base64.h"
#include "http_auth.h"
#include "plugin.h"
#include <stdlib.h>
#include <string.h>
#include "sys-crypto-md.h"
#ifdef USE_LIB_CRYPTO
#if defined(USE_NETTLE_CRYPTO)
#include <nettle/hmac.h>
#elif defined(USE_MBEDTLS_CRYPTO)
#include <mbedtls/md.h>
#elif defined(USE_OPENSSL_CRYPTO)
#include <openssl/evp.h>
#include <openssl/hmac.h>
#elif defined(USE_GNUTLS_CRYPTO)
#include <gnutls/crypto.h>
#endif
#endif
/*
* mod_secdownload verifies a checksum associated with a timestamp
* and a path.
*
* It takes an URL of the form:
* securl := <uri-prefix> <mac> <protected-path>
* uri-prefix := '/' any* # whatever was configured: must start with a '/')
* mac := [a-zA-Z0-9_-]{mac_len} # mac length depends on selected algorithm
* protected-path := '/' <timestamp> <rel-path>
* timestamp := [a-f0-9]{8} # timestamp when the checksum was calculated
* # to prevent access after timeout (active requests
* # will finish successfully even after the timeout)
* rel-path := '/' any* # the protected path; changing the path breaks the
* # checksum
*
* The timestamp is the `epoch` timestamp in hex, i.e. time in seconds
* since 00:00:00 UTC on 1 January 1970.
*
* mod_secdownload supports various MAC algorithms:
*
* # md5
* mac_len := 32 (and hex only)
* mac := md5-hex(<secrect><rel-path><timestamp>) # lowercase hex
* perl example:
use Digest::MD5 qw(md5_hex);
my $secret = "verysecret";
my $rel_path = "/index.html"
my $xtime = sprintf("%08x", time);
my $url = '/'. md5_hex($secret . $rel_path . $xtime) . '/' . $xtime . $rel_path;
*
* # hmac-sha1
* mac_len := 27 (no base64 padding)
* mac := base64-url(hmac-sha1(<secret>, <protected-path>))
* perl example:
use Digest::SHA qw(hmac_sha1);
use MIME::Base64 qw(encode_base64url);
my $secret = "verysecret";
my $rel_path = "/index.html"
my $protected_path = '/' . sprintf("%08x", time) . $rel_path;
my $url = '/'. encode_base64url(hmac_sha1($protected_path, $secret)) . $protected_path;
*
* # hmac-256
* mac_len := 43 (no base64 padding)
* mac := base64-url(hmac-256(<secret>, <protected-path>))
use Digest::SHA qw(hmac_sha256);
use MIME::Base64 qw(encode_base64url);
my $secret = "verysecret";
my $rel_path = "/index.html"
my $protected_path = '/' . sprintf("%08x", time) . $rel_path;
my $url = '/'. encode_base64url(hmac_sha256($protected_path, $secret)) . $protected_path;
*
*/
/* plugin config for all request/connections */
typedef enum {
SECDL_INVALID = 0,
SECDL_MD5 = 1,
SECDL_HMAC_SHA1 = 2,
SECDL_HMAC_SHA256 = 3,
} secdl_algorithm;
typedef struct {
const buffer *doc_root;
const buffer *secret;
const buffer *uri_prefix;
secdl_algorithm algorithm;
unsigned int timeout;
unsigned short path_segments;
unsigned short hash_querystr;
} plugin_config;
typedef struct {
PLUGIN_DATA;
plugin_config defaults;
plugin_config conf;
} plugin_data;
static int const_time_memeq(const char *a, const char *b, size_t len) {
/* constant time memory compare, unless the compiler figures it out */
char diff = 0;
size_t i;
for (i = 0; i < len; ++i) {
diff |= (a[i] ^ b[i]);
}
return 0 == diff;
}
static const char* secdl_algorithm_names[] = {
"invalid",
"md5",
"hmac-sha1",
"hmac-sha256",
};
static secdl_algorithm algorithm_from_string(const buffer *name) {
size_t ndx;
if (buffer_string_is_empty(name)) return SECDL_INVALID;
for (ndx = 1; ndx < sizeof(secdl_algorithm_names)/sizeof(secdl_algorithm_names[0]); ++ndx) {
if (0 == strcmp(secdl_algorithm_names[ndx], name->ptr)) return (secdl_algorithm)ndx;
}
return SECDL_INVALID;
}
static size_t secdl_algorithm_mac_length(secdl_algorithm alg) {
switch (alg) {
case SECDL_INVALID:
break;
case SECDL_MD5:
return 32;
case SECDL_HMAC_SHA1:
return 27;
case SECDL_HMAC_SHA256:
return 43;
}
return 0;
}
static int secdl_verify_mac(plugin_config *config, const char* protected_path, const char* mac, size_t maclen, log_error_st *errh) {
UNUSED(errh);
if (0 == maclen || secdl_algorithm_mac_length(config->algorithm) != maclen) return 0;
switch (config->algorithm) {
case SECDL_INVALID:
break;
case SECDL_MD5:
{
li_MD5_CTX Md5Ctx;
const char *ts_str;
const char *rel_uri;
unsigned char HA1[16];
unsigned char md5bin[16];
if (0 != http_auth_digest_hex2bin(mac, maclen, md5bin, sizeof(md5bin))) return 0;
/* legacy message:
* protected_path := '/' <timestamp-hex> <rel-path>
* timestamp-hex := [0-9a-f]{8}
* rel-path := '/' any*
* (the protected path was already verified)
* message = <secret><rel-path><timestamp-hex>
*/
ts_str = protected_path + 1;
rel_uri = ts_str + 8;
li_MD5_Init(&Md5Ctx);
li_MD5_Update(&Md5Ctx, CONST_BUF_LEN(config->secret));
li_MD5_Update(&Md5Ctx, rel_uri, strlen(rel_uri));
li_MD5_Update(&Md5Ctx, ts_str, 8);
li_MD5_Final(HA1, &Md5Ctx);
return const_time_memeq((char *)HA1, (char *)md5bin, sizeof(md5bin));
}
#ifdef USE_LIB_CRYPTO
case SECDL_HMAC_SHA1:
{
unsigned char digest[20];
char base64_digest[27];
#if defined(USE_NETTLE_CRYPTO)
struct hmac_sha1_ctx ctx;
hmac_sha1_set_key(&ctx, buffer_string_length(config->secret), (const uint8_t *)config->secret->ptr);
hmac_sha1_update(&ctx, strlen(protected_path), (const uint8_t *)protected_path);
hmac_sha1_digest(&ctx, sizeof(digest), (uint8_t *)digest);
#elif defined(USE_MBEDTLS_CRYPTO) && defined(MBEDTLS_MD_C) && defined(MBEDTLS_SHA1_C)
int rc =
mbedtls_md_hmac(mbedtls_md_info_from_type(MBEDTLS_MD_SHA1),
(const unsigned char *)config->secret->ptr,
buffer_string_length(config->secret),
(const unsigned char *)protected_path,
strlen(protected_path), digest);
if (0 != rc) {
log_error(errh, __FILE__, __LINE__,
"hmac-sha1: HMAC() failed");
return 0;
}
#elif defined(USE_OPENSSL_CRYPTO)
if (NULL == HMAC(
EVP_sha1(),
(unsigned char const*) config->secret->ptr, buffer_string_length(config->secret),
(unsigned char const*) protected_path, strlen(protected_path),
digest, NULL)) {
log_error(errh, __FILE__, __LINE__,
"hmac-sha1: HMAC() failed");
return 0;
}
#elif defined(USE_GNUTLS_CRYPTO)
int rc =
gnutls_hmac_fast(GNUTLS_MAC_SHA1,
(const unsigned char *)config->secret->ptr,
buffer_string_length(config->secret),
(const unsigned char *)protected_path,
strlen(protected_path), digest);
if (0 != rc) {
log_error(errh, __FILE__, __LINE__,
"hmac-sha1: HMAC() failed");
return 0;
}
#else
#error "unexpected; crypto lib not configured for use by mod_secdownload"
#endif
li_to_base64_no_padding(base64_digest, 27, digest, 20, BASE64_URL);
return (27 == maclen) && const_time_memeq(mac, base64_digest, 27);
}
break;
case SECDL_HMAC_SHA256:
{
unsigned char digest[32];
char base64_digest[43];
#if defined(USE_NETTLE_CRYPTO)
struct hmac_sha256_ctx ctx;
hmac_sha256_set_key(&ctx, buffer_string_length(config->secret), (const uint8_t *)config->secret->ptr);
hmac_sha256_update(&ctx, strlen(protected_path), (const uint8_t *)protected_path);
hmac_sha256_digest(&ctx, sizeof(digest), (uint8_t *)digest);
#elif defined(USE_MBEDTLS_CRYPTO) && defined(MBEDTLS_MD_C) && defined(MBEDTLS_SHA256_C)
int rc =
mbedtls_md_hmac(mbedtls_md_info_from_type(MBEDTLS_MD_SHA256),
(const unsigned char *)config->secret->ptr,
buffer_string_length(config->secret),
(const unsigned char *)protected_path,
strlen(protected_path), digest);
if (0 != rc) {
log_error(errh, __FILE__, __LINE__,
"hmac-sha256: HMAC() failed");
return 0;
}
#elif defined(USE_OPENSSL_CRYPTO)
if (NULL == HMAC(
EVP_sha256(),
(unsigned char const*) config->secret->ptr, buffer_string_length(config->secret),
(unsigned char const*) protected_path, strlen(protected_path),
digest, NULL)) {
log_error(errh, __FILE__, __LINE__,
"hmac-sha256: HMAC() failed");
return 0;
}
#elif defined(USE_GNUTLS_CRYPTO)
int rc =
gnutls_hmac_fast(GNUTLS_MAC_SHA256,
(const unsigned char *)config->secret->ptr,
buffer_string_length(config->secret),
(const unsigned char *)protected_path,
strlen(protected_path), digest);
if (0 != rc) {
log_error(errh, __FILE__, __LINE__,
"hmac-sha256: HMAC() failed");
return 0;
}
#else
#error "unexpected; crypto lib not configured for use by mod_secdownload"
#endif
li_to_base64_no_padding(base64_digest, 43, digest, 32, BASE64_URL);
return (43 == maclen) && const_time_memeq(mac, base64_digest, 43);
}
break;
#endif
default:
break;
}
return 0;
}
INIT_FUNC(mod_secdownload_init) {
return calloc(1, sizeof(plugin_data));
}
static int mod_secdownload_parse_algorithm(config_plugin_value_t * const cpv, log_error_st * const errh) {
secdl_algorithm algorithm = algorithm_from_string(cpv->v.b);
switch (algorithm) {
case SECDL_INVALID:
log_error(errh, __FILE__, __LINE__,
"invalid secdownload.algorithm: %s", cpv->v.b->ptr);
return 0;
#ifndef USE_LIB_CRYPTO
case SECDL_HMAC_SHA1:
case SECDL_HMAC_SHA256:
log_error(errh, __FILE__, __LINE__,
"unsupported secdownload.algorithm: %s", cpv->v.b->ptr);
/*return 0;*/
/* proceed to allow config to load for other tests */
/* (use of unsupported algorithm will result in failure at runtime) */
break;
#endif
default:
break;
}
cpv->vtype = T_CONFIG_INT;
cpv->v.u = algorithm;
return 1;
}
static void mod_secdownload_merge_config_cpv(plugin_config * const pconf, const config_plugin_value_t * const cpv) {
switch (cpv->k_id) { /* index into static config_plugin_keys_t cpk[] */
case 0: /* secdownload.secret */
pconf->secret = cpv->v.b;
break;
case 1: /* secdownload.document-root */
pconf->doc_root = cpv->v.b;
break;
case 2: /* secdownload.uri-prefix */
pconf->uri_prefix = cpv->v.b;
break;
case 3: /* secdownload.timeout */
pconf->timeout = cpv->v.u;
break;
case 4: /* secdownload.algorithm */
pconf->algorithm = cpv->v.u; /* mod_secdownload_parse_algorithm() */
break;
case 5: /* secdownload.path-segments */
pconf->path_segments = cpv->v.shrt;
break;
case 6: /* secdownload.hash-querystr */
pconf->hash_querystr = cpv->v.u;
break;
default:/* should not happen */
return;
}
}
static void mod_secdownload_merge_config(plugin_config * const pconf, const config_plugin_value_t *cpv) {
do {
mod_secdownload_merge_config_cpv(pconf, cpv);
} while ((++cpv)->k_id != -1);
}
static void mod_secdownload_patch_config(request_st * const r, plugin_data * const p) {
memcpy(&p->conf, &p->defaults, sizeof(plugin_config));
for (int i = 1, used = p->nconfig; i < used; ++i) {
if (config_check_cond(r, (uint32_t)p->cvlist[i].k_id))
mod_secdownload_merge_config(&p->conf, p->cvlist + p->cvlist[i].v.u2[0]);
}
}
SETDEFAULTS_FUNC(mod_secdownload_set_defaults) {
static const config_plugin_keys_t cpk[] = {
{ CONST_STR_LEN("secdownload.secret"),
T_CONFIG_STRING,
T_CONFIG_SCOPE_CONNECTION }
,{ CONST_STR_LEN("secdownload.document-root"),
T_CONFIG_STRING,
T_CONFIG_SCOPE_CONNECTION }
,{ CONST_STR_LEN("secdownload.uri-prefix"),
T_CONFIG_STRING,
T_CONFIG_SCOPE_CONNECTION }
,{ CONST_STR_LEN("secdownload.timeout"),
T_CONFIG_INT,
T_CONFIG_SCOPE_CONNECTION }
,{ CONST_STR_LEN("secdownload.algorithm"),
T_CONFIG_STRING,
T_CONFIG_SCOPE_CONNECTION }
,{ CONST_STR_LEN("secdownload.path-segments"),
T_CONFIG_SHORT,
T_CONFIG_SCOPE_CONNECTION }
,{ CONST_STR_LEN("secdownload.hash-querystr"),
T_CONFIG_BOOL,
T_CONFIG_SCOPE_CONNECTION }
,{ NULL, 0,
T_CONFIG_UNSET,
T_CONFIG_SCOPE_UNSET }
};
plugin_data * const p = p_d;
if (!config_plugin_values_init(srv, p, cpk, "mod_secdownload"))
return HANDLER_ERROR;
/* process and validate config directives
* (init i to 0 if global context; to 1 to skip empty global context) */
for (int i = !p->cvlist[0].v.u2[1]; i < p->nconfig; ++i) {
config_plugin_value_t *cpv = p->cvlist + p->cvlist[i].v.u2[0];
for (; -1 != cpv->k_id; ++cpv) {
switch (cpv->k_id) {
case 0: /* secdownload.secret */
case 1: /* secdownload.document-root */
case 2: /* secdownload.uri-prefix */
case 3: /* secdownload.timeout */
break;
case 4: /* secdownload.algorithm */
if (!mod_secdownload_parse_algorithm(cpv, srv->errh))
return HANDLER_ERROR;
break;
case 5: /* secdownload.path-segments */
case 6: /* secdownload.hash-querystr */
break;
default:/* should not happen */
break;
}
}
}
p->defaults.timeout = 60;
/* initialize p->defaults from global config context */
if (p->nconfig > 0 && p->cvlist->v.u2[1]) {
const config_plugin_value_t *cpv = p->cvlist + p->cvlist->v.u2[0];
if (-1 != cpv->k_id)
mod_secdownload_merge_config(&p->defaults, cpv);
}
return HANDLER_GO_ON;
}
/**
* checks if the supplied string is a hex string
*
* @param str a possible hex string
* @return if the supplied string is a valid hex string 1 is returned otherwise 0
*/
static int is_hex_len(const char *str, size_t len) {
size_t i;
if (NULL == str) return 0;
for (i = 0; i < len && *str; i++, str++) {
/* illegal characters */
if (!((*str >= '0' && *str <= '9') ||
(*str >= 'a' && *str <= 'f') ||
(*str >= 'A' && *str <= 'F'))
) {
return 0;
}
}
return i == len;
}
/**
* checks if the supplied string is a base64 (modified URL) string
*
* @param str a possible base64 (modified URL) string
* @return if the supplied string is a valid base64 (modified URL) string 1 is returned otherwise 0
*/
static int is_base64_len(const char *str, size_t len) {
size_t i;
if (NULL == str) return 0;
for (i = 0; i < len && *str; i++, str++) {
/* illegal characters */
if (!((*str >= '0' && *str <= '9') ||
(*str >= 'a' && *str <= 'z') ||
(*str >= 'A' && *str <= 'Z') ||
(*str == '-') || (*str == '_'))
) {
return 0;
}
}
return i == len;
}
URIHANDLER_FUNC(mod_secdownload_uri_handler) {
plugin_data *p = p_d;
const char *rel_uri, *ts_str, *mac_str, *protected_path;
time_t ts = 0;
size_t i, mac_len;
if (NULL != r->handler_module) return HANDLER_GO_ON;
#ifdef __COVERITY__
if (buffer_is_empty(&r->uri.path)) return HANDLER_GO_ON;
#endif
mod_secdownload_patch_config(r, p);
if (buffer_string_is_empty(p->conf.uri_prefix)) return HANDLER_GO_ON;
if (buffer_string_is_empty(p->conf.secret)) {
log_error(r->conf.errh, __FILE__, __LINE__,
"secdownload.secret has to be set");
r->http_status = 500;
return HANDLER_FINISHED;
}
if (buffer_string_is_empty(p->conf.doc_root)) {
log_error(r->conf.errh, __FILE__, __LINE__,
"secdownload.document-root has to be set");
r->http_status = 500;
return HANDLER_FINISHED;
}
if (SECDL_INVALID == p->conf.algorithm) {
log_error(r->conf.errh, __FILE__, __LINE__,
"secdownload.algorithm has to be set");
r->http_status = 500;
return HANDLER_FINISHED;
}
mac_len = secdl_algorithm_mac_length(p->conf.algorithm);
if (0 != strncmp(r->uri.path.ptr, p->conf.uri_prefix->ptr, buffer_string_length(p->conf.uri_prefix))) return HANDLER_GO_ON;
mac_str = r->uri.path.ptr + buffer_string_length(p->conf.uri_prefix);
if (!is_base64_len(mac_str, mac_len)) return HANDLER_GO_ON;
protected_path = mac_str + mac_len;
if (*protected_path != '/') return HANDLER_GO_ON;
ts_str = protected_path + 1;
if (!is_hex_len(ts_str, 8)) return HANDLER_GO_ON;
if (*(ts_str + 8) != '/') return HANDLER_GO_ON;
for (i = 0; i < 8; i++) {
ts = (ts << 4) + hex2int(ts_str[i]);
}
const time_t cur_ts = log_epoch_secs;
/* timed-out */
if ( (cur_ts > ts && (unsigned int) (cur_ts - ts) > p->conf.timeout) ||
(cur_ts < ts && (unsigned int) (ts - cur_ts) > p->conf.timeout) ) {
/* "Gone" as the url will never be valid again instead of "408 - Timeout" where the request may be repeated */
r->http_status = 410;
return HANDLER_FINISHED;
}
rel_uri = ts_str + 8;
buffer * const tb = r->tmp_buf;
if (p->conf.path_segments) {
const char *rel_uri_end = rel_uri;
unsigned int count = p->conf.path_segments;
do {
rel_uri_end = strchr(rel_uri_end+1, '/');
} while (rel_uri_end && --count);
if (rel_uri_end) {
buffer_copy_string_len(tb, protected_path,
rel_uri_end - protected_path);
protected_path = tb->ptr;
}
}
if (p->conf.hash_querystr && !buffer_is_empty(&r->uri.query)) {
if (protected_path != tb->ptr) {
buffer_copy_string(tb, protected_path);
}
buffer_append_string_len(tb, CONST_STR_LEN("?"));
buffer_append_string_buffer(tb, &r->uri.query);
/* assign last in case tb->ptr is reallocated */
protected_path = tb->ptr;
}
if (!secdl_verify_mac(&p->conf, protected_path, mac_str, mac_len,
r->conf.errh)) {
r->http_status = 403;
if (r->conf.log_request_handling) {
log_error(r->conf.errh, __FILE__, __LINE__,
"mac invalid: %s", r->uri.path.ptr);
}
return HANDLER_FINISHED;
}
/* starting with the last / we should have relative-path to the docroot
*/
buffer_copy_buffer(&r->physical.doc_root, p->conf.doc_root);
buffer_copy_buffer(&r->physical.basedir, p->conf.doc_root);
buffer_copy_string(&r->physical.rel_path, rel_uri);
buffer_copy_buffer(&r->physical.path, &r->physical.doc_root);
buffer_append_string_buffer(&r->physical.path, &r->physical.rel_path);
return HANDLER_GO_ON;
}
int mod_secdownload_plugin_init(plugin *p);
int mod_secdownload_plugin_init(plugin *p) {
p->version = LIGHTTPD_VERSION_ID;
p->name = "secdownload";
p->init = mod_secdownload_init;
p->handle_physical = mod_secdownload_uri_handler;
p->set_defaults = mod_secdownload_set_defaults;
return 0;
}
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