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From 1cb2420a26924ea4b4a5b525a78cdd06e4f9e4fa Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Tue, 26 Nov 2019 19:30:10 -0800
Subject: [PATCH] cbor, u2f: avoid use of packed struct
---
src/cbor.c | 14 ++++++++--
src/fido/types.h | 13 ++-------
src/u2f.c | 70 +++++++++++++++++++++++++++++++++---------------
3 files changed, 62 insertions(+), 35 deletions(-)
diff --git a/src/cbor.c b/src/cbor.c
index 3928325..2b3c150 100644
--- a/src/cbor.c
+++ b/src/cbor.c
@@ -1278,7 +1278,12 @@ cbor_decode_cred_authdata(const cbor_item_t *item, int cose_alg,
fido_log_debug("%s: buf=%p, len=%zu", __func__, (const void *)buf, len);
fido_log_xxd(buf, len);
- if (fido_buf_read(&buf, &len, authdata, sizeof(*authdata)) < 0) {
+ if (fido_buf_read(&buf, &len, authdata->rp_id_hash,
+ sizeof(authdata->rp_id_hash)) < 0 ||
+ fido_buf_read(&buf, &len, &authdata->flags,
+ sizeof(authdata->flags)) < 0 ||
+ fido_buf_read(&buf, &len, &authdata->sigcount,
+ sizeof(authdata->sigcount)) < 0) {
fido_log_debug("%s: fido_buf_read", __func__);
return (-1);
}
@@ -1328,7 +1333,12 @@ cbor_decode_assert_authdata(const cbor_item_t *item, fido_blob_t *authdata_cbor,
fido_log_debug("%s: buf=%p, len=%zu", __func__, (const void *)buf, len);
- if (fido_buf_read(&buf, &len, authdata, sizeof(*authdata)) < 0) {
+ if (fido_buf_read(&buf, &len, authdata->rp_id_hash,
+ sizeof(authdata->rp_id_hash)) < 0 ||
+ fido_buf_read(&buf, &len, &authdata->flags,
+ sizeof(authdata->flags)) < 0 ||
+ fido_buf_read(&buf, &len, &authdata->sigcount,
+ sizeof(authdata->sigcount)) < 0) {
fido_log_debug("%s: fido_buf_read", __func__);
return (-1);
}
diff --git a/src/fido/types.h b/src/fido/types.h
index a8ce2ec..814f22c 100644
--- a/src/fido/types.h
+++ b/src/fido/types.h
@@ -44,7 +44,6 @@ typedef enum {
typedef void fido_log_handler_t(const char *);
#ifdef _FIDO_INTERNAL
-#include "packed.h"
#include "blob.h"
/* COSE ES256 (ECDSA over P-256 with SHA-256) public key */
@@ -69,20 +68,12 @@ typedef struct eddsa_pk {
unsigned char x[32];
} eddsa_pk_t;
-PACKED_TYPE(fido_authdata_t,
-struct fido_authdata {
+typedef struct fido_authdata {
unsigned char rp_id_hash[32]; /* sha256 of fido_rp.id */
uint8_t flags; /* user present/verified */
uint32_t sigcount; /* signature counter */
/* actually longer */
-})
-
-PACKED_TYPE(fido_attcred_raw_t,
-struct fido_attcred_raw {
- unsigned char aaguid[16]; /* credential's aaguid */
- uint16_t id_len; /* credential id length */
- uint8_t body[]; /* credential id + pubkey */
-})
+} fido_authdata_t;
typedef struct fido_attcred {
unsigned char aaguid[16]; /* credential's aaguid */
diff --git a/src/u2f.c b/src/u2f.c
index 3b01f61..848d2fb 100644
--- a/src/u2f.c
+++ b/src/u2f.c
@@ -16,6 +16,29 @@
#include "fido.h"
#include "fido/es256.h"
+/*
+ * Web Authentication section 6.1
+ * https://www.w3.org/TR/webauthn/#authenticator-data
+ */
+enum {
+ AUTHDATA_RP_ID_HASH = 0,
+ AUTHDATA_FLAGS = 32,
+ AUTHDATA_SIGN_COUNT = 33,
+
+ AUTHDATA_BASE_SIZE = 37
+};
+
+/*
+ * Web Authentication section 6.4.1
+ * https://www.w3.org/TR/webauthn/#sec-attested-credential-data
+ */
+enum {
+ ATTCRED_AAGUID = 0,
+ ATTCRED_CREDENTIAL_ID_LENGTH = 16,
+
+ ATTCRED_BASE_SIZE = 18
+};
+
static int
sleep_msec(unsigned int msec)
{
@@ -96,23 +119,24 @@ static int
authdata_fake(const char *rp_id, uint8_t flags, uint32_t sigcount,
fido_blob_t *fake_cbor_ad)
{
- fido_authdata_t ad;
+ uint8_t authdata[AUTHDATA_BASE_SIZE] = {0};
+ unsigned char *rp_id_hash;
cbor_item_t *item = NULL;
size_t alloc_len;
- memset(&ad, 0, sizeof(ad));
+ rp_id_hash = (unsigned char *)&authdata[AUTHDATA_RP_ID_HASH];
if (SHA256((const void *)rp_id, strlen(rp_id),
- ad.rp_id_hash) != ad.rp_id_hash) {
+ rp_id_hash) != rp_id_hash) {
fido_log_debug("%s: sha256", __func__);
return (-1);
}
- ad.flags = flags; /* XXX translate? */
- ad.sigcount = sigcount;
+ authdata[AUTHDATA_FLAGS] = flags; /* XXX translate? */
+ memcpy(&authdata[AUTHDATA_SIGN_COUNT], &sigcount, 4);
- if ((item = cbor_build_bytestring((const unsigned char *)&ad,
- sizeof(ad))) == NULL) {
+ if ((item = cbor_build_bytestring((cbor_data)authdata,
+ sizeof(authdata))) == NULL) {
fido_log_debug("%s: cbor_build_bytestring", __func__);
return (-1);
}
@@ -410,18 +434,18 @@ static int
encode_cred_authdata(const char *rp_id, const uint8_t *kh, uint8_t kh_len,
const uint8_t *pubkey, size_t pubkey_len, fido_blob_t *out)
{
- fido_authdata_t authdata;
- fido_attcred_raw_t attcred_raw;
- fido_blob_t pk_blob;
- fido_blob_t authdata_blob;
- cbor_item_t *authdata_cbor = NULL;
- unsigned char *ptr;
- size_t len;
- size_t alloc_len;
- int ok = -1;
+ uint8_t authdata[AUTHDATA_BASE_SIZE] = {0};
+ unsigned char *rp_id_hash;
+ uint8_t attcred_raw[ATTCRED_BASE_SIZE] = {0};
+ fido_blob_t pk_blob;
+ fido_blob_t authdata_blob;
+ cbor_item_t *authdata_cbor = NULL;
+ unsigned char *ptr;
+ size_t len;
+ size_t alloc_len;
+ int ok = -1;
memset(&pk_blob, 0, sizeof(pk_blob));
- memset(&authdata, 0, sizeof(authdata));
memset(&authdata_blob, 0, sizeof(authdata_blob));
memset(out, 0, sizeof(*out));
@@ -435,17 +459,19 @@ encode_cred_authdata(const char *rp_id, const uint8_t *kh, uint8_t kh_len,
goto fail;
}
+ rp_id_hash = (unsigned char *)&authdata[AUTHDATA_RP_ID_HASH];
+
if (SHA256((const void *)rp_id, strlen(rp_id),
- authdata.rp_id_hash) != authdata.rp_id_hash) {
+ rp_id_hash) != rp_id_hash) {
fido_log_debug("%s: sha256", __func__);
goto fail;
}
- authdata.flags = (CTAP_AUTHDATA_ATT_CRED | CTAP_AUTHDATA_USER_PRESENT);
- authdata.sigcount = 0;
+ authdata[AUTHDATA_FLAGS] = (CTAP_AUTHDATA_ATT_CRED |
+ CTAP_AUTHDATA_USER_PRESENT);
- memset(&attcred_raw.aaguid, 0, sizeof(attcred_raw.aaguid));
- attcred_raw.id_len = htobe16(kh_len);
+ /* big-endian, so second byte is LSB */
+ attcred_raw[ATTCRED_CREDENTIAL_ID_LENGTH + 1] = kh_len;
len = authdata_blob.len = sizeof(authdata) + sizeof(attcred_raw) +
kh_len + pk_blob.len;
--
2.26.1
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