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awsrequest.c
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awsrequest.c
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#include <curl/curl.h>
#include <json/json.h>
#include <apr-1/apr_errno.h>
#include <apr-1/apr_pools.h>
#include <apr-1/apr_tables.h>
#include <apr-1/apr_strings.h>
#include <openssl/evp.h>
#include <openssl/hmac.h>
#include <ctype.h>
// aws credentials
static struct
{
char access_key_id[128];
char secret_access_key[128];
char token[1024];
} creds;
// buffer for capturing curl responses
static struct memstruct
{
char *data;
size_t size;
} curlmemstruct;
const char *local_region = NULL;
// callback for capturing curl responses in memory
static size_t curl_writemem_callback(void *contents, size_t size, size_t nmemb, void *userp)
{
size_t realsize = size * nmemb;
struct memstruct *mem = (struct memstruct *)userp;
mem->data = realloc(mem->data, mem->size + realsize + 1);
if(mem->data == NULL)
return 0;
memcpy(&(mem->data[mem->size]), contents, realsize);
mem->size += realsize;
mem->data[mem->size] = 0;
return realsize;
}
// use EC2 instance metadata to get temporary AWS credentials
int init_aws_creds_from_role()
{
CURL *ch;
json_object *credobj, *tmpobj;
json_bool jsonret;
CURLcode res;
char credpath[256] = "http://169.254.169.254/2014-11-05/meta-data/iam/security-credentials/";
// curl for the name of our credentials
curlmemstruct.data = malloc(sizeof(char));
*(curlmemstruct.data) = 0;
curlmemstruct.size = 0;
ch = curl_easy_init();
if(!ch)
{
return -1;
}
curl_easy_setopt(ch, CURLOPT_URL, credpath);
curl_easy_setopt(ch, CURLOPT_WRITEFUNCTION, curl_writemem_callback);
curl_easy_setopt(ch, CURLOPT_WRITEDATA, &curlmemstruct);
res = curl_easy_perform(ch);
if(res != CURLE_OK)
{
return -1;
}
curl_easy_cleanup(ch);
// append the name of the creds to the creds url
strncat(credpath, curlmemstruct.data, sizeof(credpath) - strlen(credpath) - 1);
// curl for the actual credentials document
free(curlmemstruct.data);
curlmemstruct.data = malloc(sizeof(char));
*(curlmemstruct.data) = 0;
curlmemstruct.size = 0;
ch = curl_easy_init();
if(!ch)
return -1;
curl_easy_setopt(ch, CURLOPT_URL, credpath);
curl_easy_setopt(ch, CURLOPT_WRITEFUNCTION, curl_writemem_callback);
curl_easy_setopt(ch, CURLOPT_WRITEDATA, &curlmemstruct);
res = curl_easy_perform(ch);
if(res != CURLE_OK)
return -1;
curl_easy_cleanup(ch);
// parse out the relevant credential details
credobj = json_tokener_parse(curlmemstruct.data);
jsonret = json_object_object_get_ex(credobj, "AccessKeyId", &tmpobj);
if(!jsonret)
return -1;
creds.access_key_id[0] = 0;
strncpy(creds.access_key_id, json_object_get_string(tmpobj), sizeof(creds.access_key_id));
json_object_put(tmpobj);
jsonret = json_object_object_get_ex(credobj, "SecretAccessKey", &tmpobj);
if(!jsonret)
return -1;
creds.secret_access_key[0] = 0;
strncpy(creds.secret_access_key, json_object_get_string(tmpobj), sizeof(creds.secret_access_key));
json_object_put(tmpobj);
jsonret = json_object_object_get_ex(credobj, "Token", &tmpobj);
if(!jsonret)
return -1;
creds.token[0] = 0;
strncpy(creds.token, json_object_get_string(tmpobj), sizeof(creds.token));
json_object_put(tmpobj);
json_object_put(credobj);
free(curlmemstruct.data);
return 0;
}
// create a new copy of s from pool and return it lower-cased
static char *pstrtolower(apr_pool_t *pool, const char *s)
{
char *ret = apr_pstrdup(pool, s);
char *tmp;
for(tmp = ret; *tmp; tmp++)
*tmp = tolower(*tmp);
return ret;
}
// callback for getting apr_table_t * keys
static int _get_apr_table_keys_callback(void *data, const char *key, const char *value)
{
apr_array_header_t *arr = data;
*(const char **)apr_array_push(arr) = apr_pstrdup(arr->pool, key);
return 1;
}
// return all the keys from an apr_table_t * as an apr_array_header_t *
static apr_array_header_t *get_apr_table_keys(apr_pool_t *pool, apr_table_t *table)
{
apr_array_header_t *ret = apr_array_make(pool, 16, sizeof(const char *));
apr_table_do(_get_apr_table_keys_callback, ret, table, NULL);
return ret;
}
// combo of an apr memory pool and curl_slist
static struct {
apr_pool_t *pool;
struct curl_slist *slist;
} pool_slist;
// convert apr_table into curl slist for setting HTTP headers
static int _header_table_to_slist_callback(void *data, const char *key, const char *value)
{
pool_slist.slist = curl_slist_append(pool_slist.slist, apr_pstrcat(pool_slist.pool, key, ": ", value, NULL));
return 1;
}
// callback for sorting apr_array_header_t * in place - dereference and compare
static int _sort_apr_array_case_callback(const void *v1, const void *v2)
{
// dereference the strings to compare
const char *s1 = *(const char **)v1;
const char *s2 = *(const char **)v2;
// return the case-insensitive comparison
return strcasecmp(s1, s2);
}
// sort an apr_array_header_t * in place
static void sort_apr_array_case(apr_array_header_t *arr)
{
qsort(arr->elts, arr->nelts, arr->elt_size, _sort_apr_array_case_callback);
}
// calculate sha256 hash and hex-encode into a pool-allocated buffer
static char *psha256hex(apr_pool_t *pool, const char *message, size_t message_size)
{
EVP_MD_CTX *mdctx;
const EVP_MD *md;
unsigned char md_value[EVP_MAX_MD_SIZE];
int i;
unsigned int md_len;
char *ret, *tmp;
ret = apr_pcalloc(pool, (256 / 4 + 1 ) * sizeof(char));
// calculate the hash
OpenSSL_add_all_digests();
md = EVP_sha256();
mdctx = EVP_MD_CTX_create();
EVP_DigestInit_ex(mdctx, md, NULL);
EVP_DigestUpdate(mdctx, message, message_size);
EVP_DigestFinal_ex(mdctx, md_value, &md_len);
EVP_MD_CTX_destroy(mdctx);
// hex encode the output
for(i = 0, tmp = ret; i < md_len; i++, tmp += 2)
apr_snprintf(tmp, 3, "%02x", md_value[i]);
EVP_cleanup();
return ret;
}
const char *init_local_region()
{
const char url[] = "http://169.254.169.254/2014-11-05/dynamic/instance-identity/document";
CURL *ch;
CURLcode crv;
json_object *idobj, *tmpobj;
json_bool jrv;
ch = curl_easy_init();
curl_easy_setopt(ch, CURLOPT_URL, url);
curlmemstruct.data = malloc(sizeof(char));
curlmemstruct.size = 0;
curl_easy_setopt(ch, CURLOPT_WRITEFUNCTION, curl_writemem_callback);
curl_easy_setopt(ch, CURLOPT_WRITEDATA, &curlmemstruct);
crv = curl_easy_perform(ch);
if(crv != CURLE_OK)
return NULL;
curl_easy_cleanup(ch);
idobj = json_tokener_parse(curlmemstruct.data);
jrv = json_object_object_get_ex(idobj, "region", &tmpobj);
if(!jrv)
return NULL;
local_region = strdup(json_object_get_string(tmpobj));
json_object_put(tmpobj);
json_object_put(idobj);
return local_region;
}
const char *get_local_region()
{
if(local_region == NULL)
return init_local_region();
return local_region;
}
CURLcode execute_signed_aws_request(
char **return_data,
size_t *return_size,
const char *method,
const char *service,
const char *region_,
const char *hostname_,
const char *path,
apr_table_t *queryparams,
apr_table_t *headers,
const char *payload,
size_t payload_size
)
{
CURL *ch;
CURLcode status;
const char *region, *hostname;
char *canonical_request, *signed_headers, *string_to_sign, *request_signature, *tmpcp;
apr_pool_t *pool;
apr_table_t *realheaders;
apr_status_t aprv;
time_t now;
apr_array_header_t *header_keys;
int i;
unsigned int md_len;
unsigned char md_value[EVP_MAX_MD_SIZE];
char datetime[32], today[9];
// make sure we have no query params
if(queryparams != NULL)
{
*return_data = "Query Parameters are not supported (yet).";
*return_size = strlen(*return_data);
return CURLE_UNSUPPORTED_PROTOCOL;
}
// create a memory pool
aprv = apr_pool_create(&pool, NULL);
if(aprv != APR_SUCCESS)
{
*return_data = "Could not create pool.";
*return_size = strlen(*return_data);
return CURLE_OUT_OF_MEMORY;
}
// try a default region
region = region_ ? region_ : get_local_region();
if(region == NULL)
{
*return_data = "No region set and could not determine from metadata.";
*return_size = strlen(*return_data);
return CURLE_FAILED_INIT;
}
// try to build a hostname?
hostname = hostname_ ? hostname_ : apr_pstrcat(pool, service, ".", region, ".amazonaws.com", NULL);
// build the canonical request
/*
CanonicalRequest =
HTTPRequestMethod + '\n' +
CanonicalURI + '\n' +
CanonicalQueryString + '\n' +
CanonicalHeaders + '\n' +
SignedHeaders + '\n' +
HexEncode(Hash(RequestPayload))
*/
canonical_request = apr_pstrcat(pool,
method, "\n",
path, "\n",
"", "\n", // query string placeholder
NULL
);
// make a copy of the headers since we're going to add some of our own
realheaders = apr_table_clone(pool, headers);
apr_table_set(realheaders, "Host", hostname);
// calculate datetime
now = time(NULL);
strftime(datetime, sizeof(datetime), "%Y%m%dT%H%M%SZ", gmtime(&now));
apr_table_set(realheaders, "x-amz-date", datetime);
// add canonical headers
header_keys = get_apr_table_keys(pool, realheaders);
sort_apr_array_case(header_keys);
for(i = 0; i < header_keys->nelts; i++)
{
canonical_request = apr_pstrcat(pool,
canonical_request,
pstrtolower(pool, ((const char **)header_keys->elts)[i]),
":",
apr_table_get(realheaders, ((const char **)header_keys->elts)[i]),
"\n",
NULL
);
}
// add signed headers and payload hash
signed_headers = pstrtolower(pool, apr_array_pstrcat(pool, header_keys, ';'));
canonical_request = apr_pstrcat(pool, canonical_request, "\n", signed_headers, "\n", psha256hex(pool, payload, payload_size), NULL);
// build string to sign
apr_snprintf(today, 9, "%s", datetime);
string_to_sign = apr_pstrcat(pool,
"AWS4-HMAC-SHA256\n",
datetime, "\n",
today, "/", region, "/", service, "/aws4_request\n",
psha256hex(pool, canonical_request, strlen(canonical_request)),
NULL
);
// build our signing key
/*
* kSecret = Your AWS Secret Access Key
* kDate = HMAC("AWS4" + kSecret, Date)
* kRegion = HMAC(kDate, Region)
* kService = HMAC(kRegion, Service)
* kSigning = HMAC(kService, "aws4_request")
*/
HMAC(EVP_sha256(),
apr_pstrcat(pool, "AWS4", creds.secret_access_key, NULL), strlen(creds.secret_access_key) + 4,
(unsigned char *)today, 8,
md_value, &md_len
);
HMAC(EVP_sha256(),
md_value, md_len,
(unsigned char *)region, strlen(region),
md_value, &md_len
);
HMAC(EVP_sha256(),
md_value, md_len,
(unsigned char *)service, strlen(service),
md_value, &md_len
);
HMAC(EVP_sha256(),
md_value, md_len,
(unsigned char *)"aws4_request", strlen("aws4_request"),
md_value, &md_len
);
// calculate the request signature
// signature = HexEncode(HMAC(derived-signing-key, string-to-sign))
HMAC(EVP_sha256(),
md_value, md_len,
(unsigned char *)string_to_sign, strlen(string_to_sign),
md_value, &md_len
);
request_signature = apr_pcalloc(pool, 2 * md_len + 1);
for(i = 0, tmpcp = request_signature; i < md_len; i++, tmpcp += 2)
apr_snprintf(tmpcp, 3, "%02x", md_value[i]);
// build our authorization header
apr_table_set(realheaders, "Authorization", apr_pstrcat(pool,
"AWS4-HMAC-SHA256 Credential=",
creds.access_key_id, "/", today, "/", region, "/", service, "/aws4_request, ",
"SignedHeaders=", signed_headers, ", ",
"Signature=", request_signature,
NULL
)
);
// if we're using temp creds add the token
if(strlen(creds.token))
apr_table_set(realheaders, "X-Amz-Security-Token", creds.token);
// build the actual request
ch = curl_easy_init();
curl_easy_setopt(ch, CURLOPT_URL, apr_pstrcat(pool, "https://", hostname, path, NULL));
// for now treat everything like a POST
curl_easy_setopt(ch, CURLOPT_POST, 1L);
curl_easy_setopt(ch, CURLOPT_CUSTOMREQUEST, method);
if(payload_size != 0)
{
curl_easy_setopt(ch, CURLOPT_POSTFIELDSIZE, payload_size);
curl_easy_setopt(ch, CURLOPT_POSTFIELDS, payload);
}
// set request headers
pool_slist.pool = pool;
pool_slist.slist = NULL;
apr_table_do(_header_table_to_slist_callback, NULL, realheaders, NULL);
curl_easy_setopt(ch, CURLOPT_HTTPHEADER, pool_slist.slist);
// capture the output in curlmemstruct
curlmemstruct.data = malloc(sizeof(char));
curlmemstruct.size = 0;
curl_easy_setopt(ch, CURLOPT_WRITEFUNCTION, curl_writemem_callback);
curl_easy_setopt(ch, CURLOPT_WRITEDATA, &curlmemstruct);
// execute the request
status = curl_easy_perform(ch);
// copy results to a fresh non-static buffer
*return_data = calloc(curlmemstruct.size, 1);
memcpy(*return_data, curlmemstruct.data, curlmemstruct.size);
*return_size = curlmemstruct.size;
// clean up
curl_slist_free_all(pool_slist.slist);
curl_easy_cleanup(ch);
free(curlmemstruct.data);
apr_pool_destroy(pool);
return status;
}