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Fix SASL SCRAM implementation

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* Add SCRAM_DIGEST_SIZE macro for maximum possible digest size. It will
  avoid new buffer overflow errors when new digests are added.
* Fix buffer overflow in sasl_scram(). Buffers were allocated for SHA1
  digest size.
* Fix bug with handler re-registration when a SASL SCRAM mechanism
  fails.
This commit is contained in:
Dmitry Podgorny
2020-01-05 18:46:15 +02:00
parent 709e41fd10
commit 1ca10fd167
4 changed files with 38 additions and 23 deletions
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34
src/auth.c
View File

@@ -82,9 +82,9 @@ static int _handle_digestmd5_challenge(xmpp_conn_t *const conn,
static int _handle_digestmd5_rspauth(xmpp_conn_t *const conn,
xmpp_stanza_t *const stanza,
void *const userdata);
static int _handle_scram_sha1_challenge(xmpp_conn_t *const conn,
xmpp_stanza_t *const stanza,
void *const userdata);
static int _handle_scram_challenge(xmpp_conn_t *const conn,
xmpp_stanza_t *const stanza,
void *const userdata);
static char *_make_scram_init_msg(xmpp_conn_t *const conn);
static int _handle_missing_features_sasl(xmpp_conn_t *const conn,
@@ -440,18 +440,18 @@ struct scram_user_data {
};
/* handle the challenge phase of SCRAM-SHA-1 auth */
static int _handle_scram_sha1_challenge(xmpp_conn_t *const conn,
xmpp_stanza_t *const stanza,
void *const userdata)
static int _handle_scram_challenge(xmpp_conn_t *const conn,
xmpp_stanza_t *const stanza,
void *const userdata)
{
char *text;
char *response;
xmpp_stanza_t *auth;
xmpp_stanza_t *authdata;
const char *name;
const char *scram_name;
char *challenge;
struct scram_user_data *scram_ctx = (struct scram_user_data *)userdata;
int rc;
name = xmpp_stanza_get_name(stanza);
xmpp_debug(conn->ctx, "xmpp", "handle %s (challenge) called for %s",
@@ -491,14 +491,24 @@ static int _handle_scram_sha1_challenge(xmpp_conn_t *const conn,
xmpp_send(conn, auth);
xmpp_stanza_release(auth);
rc = 1; /* Keep handler */
} else {
scram_name = scram_ctx->alg->scram_name;
/*
* Free scram_ctx after calling _handle_sasl_result(). If authentication
* fails, we want to try other mechanism which may be different SCRAM
* mechanism. If we freed scram_ctx before the function, _auth() would
* be able to allocate new scram_ctx object with the same address and
* handler_add() would consider new SCRAM handler as duplicate, because
* current handler is not removed yet. As result, libstrophe wouldn't
* handle incoming challenge stanza.
*/
rc = _handle_sasl_result(conn, stanza,
(void *)scram_ctx->alg->scram_name);
xmpp_free(conn->ctx, scram_ctx->scram_init);
xmpp_free(conn->ctx, scram_ctx);
return _handle_sasl_result(conn, stanza, (void *)scram_name);
}
return 1;
return rc;
err_release_auth:
xmpp_stanza_release(auth);
@@ -694,8 +704,8 @@ static void _auth(xmpp_conn_t *const conn)
xmpp_stanza_add_child(auth, authdata);
xmpp_stanza_release(authdata);
handler_add(conn, _handle_scram_sha1_challenge, XMPP_NS_SASL, NULL,
NULL, (void *)scram_ctx);
handler_add(conn, _handle_scram_challenge, XMPP_NS_SASL, NULL, NULL,
(void *)scram_ctx);
xmpp_send(conn, auth);
xmpp_stanza_release(auth);

13
src/sasl.c
View File

@@ -21,7 +21,6 @@
#include "ostypes.h"
#include "sasl.h"
#include "md5.h"
#include "sha1.h"
#include "scram.h"
#include "rand.h"
#include "util.h"
@@ -379,7 +378,7 @@ char *sasl_digest_md5(xmpp_ctx_t *ctx,
return response;
}
/** generate auth response string for the SASL SCRAM-SHA-1 mechanism */
/** generate auth response string for the SASL SCRAM mechanism */
char *sasl_scram(xmpp_ctx_t *ctx,
const struct hash_alg *alg,
const char *challenge,
@@ -387,8 +386,8 @@ char *sasl_scram(xmpp_ctx_t *ctx,
const char *jid,
const char *password)
{
uint8_t key[SHA1_DIGEST_SIZE];
uint8_t sign[SHA1_DIGEST_SIZE];
uint8_t key[SCRAM_DIGEST_SIZE];
uint8_t sign[SCRAM_DIGEST_SIZE];
char *r = NULL;
char *s = NULL;
char *i = NULL;
@@ -439,7 +438,8 @@ char *sasl_scram(xmpp_ctx_t *ctx,
goto out_sval;
}
response_len = 39 + strlen(r);
/* "c=biws," + r + ",p=" + sign_b64 + '\0' */
response_len = 7 + strlen(r) + 3 + ((alg->digest_size + 2) / 3 * 4) + 1;
response = xmpp_alloc(ctx, response_len);
if (!response) {
goto out_auth;
@@ -454,11 +454,12 @@ char *sasl_scram(xmpp_ctx_t *ctx,
SCRAM_ClientSignature(alg, key, (uint8_t *)auth, strlen(auth), sign);
SCRAM_ClientProof(alg, sign, key, sign);
sign_b64 = xmpp_base64_encode(ctx, sign, sizeof(sign));
sign_b64 = xmpp_base64_encode(ctx, sign, alg->digest_size);
if (!sign_b64) {
goto out_response;
}
/* Check for buffer overflow */
if (strlen(response) + strlen(sign_b64) + 3 + 1 > response_len) {
xmpp_free(ctx, sign_b64);
goto out_response;

6
src/scram.c
View File

@@ -75,7 +75,7 @@ static void crypto_HMAC(const struct hash_alg *alg,
uint8_t key_pad[HMAC_BLOCK_SIZE];
uint8_t key_ipad[HMAC_BLOCK_SIZE];
uint8_t key_opad[HMAC_BLOCK_SIZE];
uint8_t sha_digest[SHA512_DIGEST_SIZE];
uint8_t sha_digest[SCRAM_DIGEST_SIZE];
int i;
union common_hash_ctx ctx;
@@ -148,7 +148,7 @@ void SCRAM_ClientKey(const struct hash_alg *alg,
uint32_t i,
uint8_t *key)
{
uint8_t salted[SHA512_DIGEST_SIZE];
uint8_t salted[SCRAM_DIGEST_SIZE];
/* XXX: Normalize(password) is omitted */
@@ -163,7 +163,7 @@ void SCRAM_ClientSignature(const struct hash_alg *alg,
size_t len,
uint8_t *sign)
{
uint8_t stored[SHA512_DIGEST_SIZE];
uint8_t stored[SCRAM_DIGEST_SIZE];
alg->hash(ClientKey, alg->digest_size, stored);
crypto_HMAC(alg, stored, alg->digest_size, AuthMessage, len, sign);

8
src/scram.h
View File

@@ -1,5 +1,5 @@
/* scram.h
* strophe XMPP client library -- SCRAM-SHA1 helper functions
* strophe XMPP client library -- SCRAM helper functions
*
* Copyright (C) 2013 Dmitry Podgorny <pasis.ua@gmail.com>
*
@@ -10,7 +10,7 @@
*/
/** @file
* SCRAM-SHA1 helper functions.
* SCRAM helper functions.
*/
#ifndef __LIBSTROPHE_SCRAM_H__
@@ -19,6 +19,10 @@
/* make sure the stdint.h types are available */
#include "ostypes.h"
/* Maximum possible digest size. Used for buffers allocation. */
#include "sha512.h"
#define SCRAM_DIGEST_SIZE SHA512_DIGEST_SIZE
struct hash_alg {
const char *scram_name;
int mask;