David Howells <dhowe...@redhat.com> wrote:
> Note, this implementation of the X.509 certificate parser uses a couple of
> patterns to drive a reusable ASN.1 decoder. I do, however, have a direct
> in-line decoder implementation also that can only decode X.509 certs. The
> stack space usage is greater, but the code size is simpler and slightly
> smaller and the code is less capable (it can't handle indefinite-length
> elements for example), and it can't be reused for anything else (such as
> CIFS, netfilter, PKCS#7, Kerberos tickets), whereas the pattern-based
> decoder can. I'll post this separately to see what people think.
Here's the direct inline X.509 ASN.1 decoder I mentioned.
David
---
/* X.509 certificate parser
*
* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowe...@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#define pr_fmt(fmt) "X.509: "fmt
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/oid_registry.h>
#include "linux/asn1.h"
#include "public_key.h"
#include "x509_parser.h"
struct x509_cursor {
unsigned start; /* Start of this element's
content */
unsigned len; /* Remaining length of
element's content */
u8 hdrlen; /* Length of header */
u8 tag; /* Tag found */
bool present; /* Element present */
};
struct x509_parse_context {
struct x509_certificate *cert; /* Certificate being
constructed */
const u8 *data; /* Start of data */
const void *cert_start; /* Start of cert content */
const void *key; /* Key data */
size_t key_size; /* Size of key data */
enum OID algo_oid; /* Algorithm OID */
unsigned char nr_mpi; /* Number of MPIs stored */
int error;
};
/*
* Free an X.509 certificate
*/
void x509_free_certificate(struct x509_certificate *cert)
{
if (cert) {
public_key_destroy(cert->pub);
kfree(cert->issuer);
kfree(cert->subject);
kfree(cert->fingerprint);
kfree(cert->authority);
kfree(cert);
}
}
/*
* Extract an ASN.1 element.
*/
static bool asn1_extract(struct x509_parse_context *ctx,
struct x509_cursor *cursor,
int expected_tag, bool optional,
struct x509_cursor *_extracted_cursor)
{
unsigned start, len;
u8 tag, l;
pr_devel("==>%s(,{%u,%u},%02x,%u) [%02x%02x]\n",
__func__, cursor->start, cursor->len, expected_tag, optional,
ctx->data[cursor->start], ctx->data[cursor->start + 1]);
if (ctx->error)
return false;
if (_extracted_cursor)
_extracted_cursor->present = false;
if (cursor->len == 0 && optional)
return false;
if (cursor->len < 2) {
pr_debug("ASN.1 elem header underrun @%u+%u\n",
cursor->start, cursor->len);
ctx->error = -EBADMSG;
return false;
}
tag = ctx->data[cursor->start];
len = ctx->data[cursor->start + 1];
if (expected_tag != -1 && tag != expected_tag) {
if (!optional) {
pr_debug("ASN.1 unexpected tag %02x%02x not %02x
@%u+%u\n",
tag, len, expected_tag,
cursor->start, cursor->len);
ctx->error = -EBADMSG;
}
return false;
}
cursor->start += 2;
cursor->len -= 2;
if ((tag & 0x1f) == 0x1f) {
pr_debug("ASN.1 long tag @%u\n", cursor->start);
ctx->error = -EBADMSG;
return false;
}
if (len == 0x80) {
pr_debug("ASN.1 indefinite length @%u\n", cursor->start);
ctx->error = -EBADMSG;
return false;
}
l = 0;
if (len > 0x80) {
l = len - 0x80;
if (cursor->len < l) {
pr_debug("ASN.1 elem len underrun (%u) @%u+%u\n",
l, cursor->start, cursor->len);
ctx->error = -EBADMSG;
return false;
}
switch (l) {
case 0x01:
len = ctx->data[cursor->start];
break;
case 0x02:
len = ctx->data[cursor->start + 0] << 8;
len += ctx->data[cursor->start + 1];
break;
case 0x03:
len = ctx->data[cursor->start + 0] << 16;
len += ctx->data[cursor->start + 1] << 8;
len += ctx->data[cursor->start + 2];
break;
case 0x04:
len = ctx->data[cursor->start + 0] << 24;
len += ctx->data[cursor->start + 1] << 16;
len += ctx->data[cursor->start + 2] << 8;
len += ctx->data[cursor->start + 3];
break;
default:
pr_debug("ASN.1 elem excessive len (%u) @%u\n",
l, cursor->start);
ctx->error = -EBADMSG;
return false;
}
cursor->start += l;
cursor->len -= l;
}
pr_debug("TAG %02x len: %u+%u\n", tag, l + 2, len);
if (cursor->len < len) {
pr_debug("ASN.1 data underrun (%u) @%u+%u\n",
len, cursor->start, cursor->len);
ctx->error = -EBADMSG;
return false;
}
start = cursor->start;
cursor->start += len;
cursor->len -= len;
if (_extracted_cursor) {
_extracted_cursor->start = start;
_extracted_cursor->len = len;
_extracted_cursor->hdrlen = 2 + l;
_extracted_cursor->tag = tag;
_extracted_cursor->present = true;
}
return true;
}
static bool asn1_check_end(struct x509_parse_context *ctx,
struct x509_cursor *cursor)
{
if (ctx->error)
return false;
if (cursor->len != 0) {
pr_debug("ASN.1 excess data @%u+%u\n",
cursor->start, cursor->len);
ctx->error = -EBADMSG;
return false;
}
return true;
}
/*
* Parse the signature type.
*/
static void x509_parse_signature_type(struct x509_parse_context *ctx,
struct x509_cursor *data)
{
struct x509_cursor type;
enum OID oid;
asn1_extract(ctx, data, ASN1_UNIV | ASN1_OID, false, &type);
asn1_extract(ctx, data, -1, true, NULL);
if (!asn1_check_end(ctx, data))
return;
oid = look_up_OID(ctx->data + type.start, type.len);
switch (oid) {
case OID_md2WithRSAEncryption:
case OID_md3WithRSAEncryption:
default:
/* Unsupported combination */
ctx->error = -ENOPKG;
return;
case OID_md4WithRSAEncryption:
ctx->cert->sig_hash_algo = PKEY_HASH_MD5;
ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
break;
case OID_sha1WithRSAEncryption:
ctx->cert->sig_hash_algo = PKEY_HASH_SHA1;
ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
break;
case OID_sha256WithRSAEncryption:
ctx->cert->sig_hash_algo = PKEY_HASH_SHA256;
ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
break;
case OID_sha384WithRSAEncryption:
ctx->cert->sig_hash_algo = PKEY_HASH_SHA384;
ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
break;
case OID_sha512WithRSAEncryption:
ctx->cert->sig_hash_algo = PKEY_HASH_SHA512;
ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
break;
case OID_sha224WithRSAEncryption:
ctx->cert->sig_hash_algo = PKEY_HASH_SHA224;
ctx->cert->sig_pkey_algo = PKEY_ALGO_RSA;
break;
}
ctx->algo_oid = oid;
}
/*
* Parse a name
*/
static void x509_parse_name(struct x509_parse_context *ctx,
struct x509_cursor *name, char **_name)
{
const u8 *data = ctx->data;
unsigned o_offset = 0, cn_offset = 0, email_offset = 0, offset;
unsigned namesize;
u8 o_size = 0, cn_size = 0, email_size = 0;
char *buffer;
BUG_ON(*_name);
while (!ctx->error && name->len > 0) {
struct x509_cursor rdn, attr, n_oid, n_val;
enum OID oid;
asn1_extract(ctx, name, ASN1_UNIV | ASN1_CONS | ASN1_SET,
false, &rdn);
while (!ctx->error && rdn.len > 0) {
asn1_extract(ctx, &rdn, ASN1_UNIV | ASN1_CONS |
ASN1_SEQ,
false, &attr);
asn1_extract(ctx, &attr, ASN1_UNIV | ASN1_OID, false,
&n_oid);
asn1_extract(ctx, &attr, -1, false, &n_val);
if (!asn1_check_end(ctx, &attr))
return;
oid = look_up_OID(data + n_oid.start, n_oid.len);
switch (oid) {
case OID_organizationName:
o_size = n_val.len;
o_offset = n_val.start;
break;
case OID_commonName:
cn_size = n_val.len;
cn_offset = n_val.start;
break;
case OID_email_address:
email_size = n_val.len;
email_offset = n_val.start;
break;
default:
continue;
}
}
if (!asn1_check_end(ctx, &rdn))
return;
}
if (!asn1_check_end(ctx, name))
return;
/* Empty name string if no material */
if (!cn_size && !o_size && !email_size) {
buffer = kmalloc(1, GFP_KERNEL);
if (!buffer) {
ctx->error = -ENOMEM;
return;
}
buffer[0] = 0;
goto done;
}
if (cn_size && o_size) {
/* Consider combining O and CN, but use only the CN if it is
* prefixed by the O, or a significant portion thereof.
*/
namesize = cn_size;
offset = cn_offset;
if (cn_size >= o_size &&
memcmp(data + cn_offset, data + o_offset, o_size) == 0)
goto single_component;
if (cn_size >= 7 &&
o_size >= 7 &&
memcmp(data + cn_offset, data + o_offset, 7) == 0)
goto single_component;
buffer = kmalloc(o_size + 2 + cn_size + 1, GFP_KERNEL);
if (!buffer) {
ctx->error = -ENOMEM;
return;
}
memcpy(buffer, data + o_offset, o_size);
buffer[o_size + 0] = ':';
buffer[o_size + 1] = ' ';
memcpy(buffer + o_size + 2, data + cn_offset, cn_size);
buffer[o_size + 2 + cn_size] = 0;
goto done;
} else if (cn_size) {
namesize = cn_size;
offset = cn_offset;
} else if (o_size) {
namesize = o_size;
offset = o_offset;
} else {
namesize = email_size;
offset = email_offset;
}
single_component:
buffer = kmalloc(namesize + 1, GFP_KERNEL);
if (!buffer) {
ctx->error = -ENOMEM;
return;
}
memcpy(buffer, data + offset, namesize);
buffer[namesize] = 0;
done:
*_name = buffer;
}
/*
* Record a certificate time.
*/
static bool x509_note_time(struct x509_parse_context *ctx,
time_t *_time, u8 tag, const u8 *value, size_t vlen)
{
unsigned YY, MM, DD, hh, mm, ss;
const u8 *p = value;
#define dec2bin(X) ((X) - '0')
#define DD2bin(P) ({ unsigned x = dec2bin(P[0]) * 10 + dec2bin(P[1]); P += 2;
x; })
if (tag == ASN1_UNITIM) {
/* UTCTime: YYMMDDHHMMSSZ */
if (vlen != 13)
goto unsupported_time;
YY = DD2bin(p);
if (YY > 50)
YY += 1900;
else
YY += 2000;
} else if (tag == ASN1_GENTIM) {
/* GenTime: YYYYMMDDHHMMSSZ */
if (vlen != 15)
goto unsupported_time;
YY = DD2bin(p) * 100 + DD2bin(p);
} else {
goto unsupported_time;
}
MM = DD2bin(p);
DD = DD2bin(p);
hh = DD2bin(p);
mm = DD2bin(p);
ss = DD2bin(p);
if (*p != 'Z')
goto unsupported_time;
*_time = mktime(YY, MM, DD, hh, mm, ss);
return true;
unsupported_time:
pr_debug("Got unsupported time [tag %02x]: '%*.*s'\n",
tag, (int)vlen, (int)vlen, value);
ctx->error = -EBADMSG;
return false;
}
/*
* Parse the validity data.
*/
static void x509_parse_validity(struct x509_parse_context *ctx,
struct x509_cursor *data)
{
struct x509_cursor not_before, not_after;
asn1_extract(ctx, data, -1, false, ¬_before);
asn1_extract(ctx, data, -1, false, ¬_after);
if (!asn1_check_end(ctx, data))
return;
if (x509_note_time(ctx, &ctx->cert->valid_from, not_before.tag,
ctx->data + not_before.start, not_before.len) < 0) {
ctx->error = -EBADMSG;
return;
}
if (x509_note_time(ctx, &ctx->cert->valid_to, not_after.tag,
ctx->data + not_after.start, not_after.len) < 0) {
ctx->error = -EBADMSG;
return;
}
}
/*
* Extract a RSA public key value
*/
static void x509_parse_rsa_key(struct x509_parse_context *ctx,
struct x509_cursor *data)
{
struct x509_cursor list, integer;
MPI mpi;
asn1_extract(ctx, data, ASN1_UNIV | ASN1_CONS | ASN1_SEQ, false, &list);
if (!asn1_check_end(ctx, data))
return;
while (list.len > 0) {
if (ctx->nr_mpi >= ARRAY_SIZE(ctx->cert->pub->mpi)) {
pr_debug("Too many public key MPIs in certificate\n");
ctx->error = -EBADMSG;
return;
}
if (!asn1_extract(ctx, &list, ASN1_UNIV | ASN1_INT,
false, &integer))
return;
mpi = mpi_read_raw_data(ctx->data + integer.start, integer.len);
if (!mpi) {
ctx->error = -ENOMEM;
return;
}
ctx->cert->pub->mpi[ctx->nr_mpi++] = mpi;
}
asn1_check_end(ctx, &list);
}
/*
* Parse the key.
*/
static void x509_parse_key(struct x509_parse_context *ctx,
struct x509_cursor *data)
{
struct x509_cursor algo, type, str;
enum OID oid;
asn1_extract(ctx, data, ASN1_UNIV | ASN1_CONS | ASN1_SEQ, false, &algo);
asn1_extract(ctx, data, ASN1_UNIV | ASN1_BTS, false, &str);
if (!asn1_check_end(ctx, data))
return;
asn1_extract(ctx, &algo, ASN1_UNIV | ASN1_OID, false, &type);
asn1_extract(ctx, &algo, -1, true, NULL);
if (!asn1_check_end(ctx, &algo))
return;
oid = look_up_OID(ctx->data + type.start, type.len);
if (oid != OID_rsaEncryption) {
ctx->error = -ENOPKG;
return;
}
ctx->cert->pkey_algo = PKEY_ALGO_RSA;
/* Remove the bit string's initial unused bit count */
if (str.len < 1) {
pr_debug("ASN.1 short BIT STRING @%u+%u\n", str.start, str.len);
ctx->error = -EBADMSG;
return;
}
str.start++;
str.len--;
x509_parse_rsa_key(ctx, &str);
}
/*
* Parse the extension list.
*/
static void x509_parse_extensions(struct x509_parse_context *ctx,
struct x509_cursor *data)
{
struct x509_cursor extensions, ext;
char *f;
if (!data->present)
return;
asn1_extract(ctx, data, ASN1_UNIV | ASN1_CONS | ASN1_SEQ, false,
&extensions);
if (!asn1_check_end(ctx, data))
return;
while (extensions.len > 0 &&
asn1_extract(ctx, &extensions, ASN1_UNIV | ASN1_CONS | ASN1_SEQ,
false, &ext)
) {
struct x509_cursor type, val, wrapper, part;
const u8 *v;
enum OID oid;
int i;
asn1_extract(ctx, &ext, ASN1_UNIV | ASN1_OID, false, &type);
asn1_extract(ctx, &ext, ASN1_UNIV | ASN1_BOOL, true, NULL);
asn1_extract(ctx, &ext, ASN1_UNIV | ASN1_OTS, false, &val);
if (!asn1_check_end(ctx, &ext))
return;
oid = look_up_OID(ctx->data + type.start, type.len);
switch (oid) {
case OID_subjectKeyIdentifier:
/* Get hold of the key fingerprint */
asn1_extract(ctx, &val, ASN1_UNIV | ASN1_OTS, false,
&part);
if (!asn1_check_end(ctx, &val))
return;
if (part.len == 0) {
pr_debug("Empty subjectKeyIdentifier\n");
ctx->error = -EBADMSG;
return;
}
f = kmalloc(part.len * 2 + 1, GFP_KERNEL);
if (!f) {
ctx->error = -ENOMEM;
return;
}
v = ctx->data + part.start;
for (i = 0; i < part.len; i++)
sprintf(f + i * 2, "%02x", v[i]);
pr_debug("fingerprint %s\n", f);
ctx->cert->fingerprint = f;
break;
case OID_authorityKeyIdentifier:
/* Get hold of the CA key fingerprint */
asn1_extract(ctx, &val, ASN1_UNIV | ASN1_CONS |
ASN1_SEQ,
false, &wrapper);
if (!asn1_check_end(ctx, &val))
return;
asn1_extract(ctx, &wrapper, ASN1_CONT | 0, false,
&part);
if (!asn1_check_end(ctx, &wrapper))
return;
if (part.len == 0) {
pr_debug("Empty authorityKeyIdentifier\n");
ctx->error = -EBADMSG;
return;
}
f = kmalloc(part.len * 2 + 1, GFP_KERNEL);
if (!f) {
ctx->error = -ENOMEM;
return;
}
v = ctx->data + part.start;
for (i = 0; i < part.len; i++)
sprintf(f + i * 2, "%02x", v[i]);
pr_debug("authority %s\n", f);
ctx->cert->authority = f;
break;
default:
continue;
}
}
asn1_check_end(ctx, &extensions);
}
/*
* Parse the signature algorithm.
*/
static void x509_parse_signature_algo(struct x509_parse_context *ctx,
struct x509_cursor *data)
{
struct x509_cursor type;
enum OID oid;
asn1_extract(ctx, data, ASN1_UNIV | ASN1_OID, false, &type);
asn1_extract(ctx, data, -1, true, NULL);
if (!asn1_check_end(ctx, data))
return;
oid = look_up_OID(ctx->data + type.start, type.len);
pr_debug("Signature type: %u\n", oid);
if (oid != ctx->algo_oid) {
pr_debug("Got cert with pkey (%u) and sig (%u) algorithm
OIDs\n",
ctx->algo_oid, oid);
ctx->error = -EINVAL;
}
}
/*
* Parse the basic structure of the certificate.
*/
static void x509_parse_basic(struct x509_parse_context *ctx,
size_t datalen)
{
struct x509_cursor cert, tbs;
struct x509_cursor tmp = {
.start = 0,
.len = datalen
};
if (!asn1_extract(ctx, &tmp, ASN1_UNIV | ASN1_CONS | ASN1_SEQ,
false, &cert) ||
!asn1_check_end(ctx, &tmp))
return;
if (!asn1_extract(ctx, &cert, ASN1_UNIV | ASN1_CONS | ASN1_SEQ,
false, &tbs))
return;
pr_debug("x509_note_tbs_certificate(,%02x,%u,%u)!\n",
tbs.tag, tbs.start, tbs.len);
ctx->cert->tbs = ctx->data + (tbs.start - tbs.hdrlen);
ctx->cert->tbs_size = tbs.hdrlen + tbs.len;
{
asn1_extract(ctx, &tbs, ASN1_CONT | ASN1_CONS | 0,
true, NULL); /* Version */
asn1_extract(ctx, &tbs, ASN1_UNIV | ASN1_INT,
false, NULL); /* Serial */
asn1_extract(ctx, &tbs, ASN1_UNIV | ASN1_CONS | ASN1_SEQ,
false, &tmp);
x509_parse_signature_type(ctx, &tmp);
asn1_extract(ctx, &tbs, ASN1_UNIV | ASN1_CONS | ASN1_SEQ,
false, &tmp);
x509_parse_name(ctx, &tmp, &ctx->cert->issuer);
asn1_extract(ctx, &tbs, ASN1_UNIV | ASN1_CONS | ASN1_SEQ,
false, &tmp);
x509_parse_validity(ctx, &tmp);
asn1_extract(ctx, &tbs, ASN1_UNIV | ASN1_CONS | ASN1_SEQ,
false, &tmp);
x509_parse_name(ctx, &tmp, &ctx->cert->subject);
asn1_extract(ctx, &tbs, ASN1_UNIV | ASN1_CONS | ASN1_SEQ,
false, &tmp);
x509_parse_key(ctx, &tmp);
asn1_extract(ctx, &tbs, ASN1_CONT | ASN1_CONS | 1,
true, NULL); /* Issuer uid */
asn1_extract(ctx, &tbs, ASN1_CONT | ASN1_CONS | 2,
true, NULL); /* Subject uid */
asn1_extract(ctx, &tbs, ASN1_CONT | ASN1_CONS | 3,
true, &tmp);
x509_parse_extensions(ctx, &tmp);
}
if (!asn1_check_end(ctx, &tbs))
return;
asn1_extract(ctx, &cert, ASN1_UNIV | ASN1_CONS | ASN1_SEQ,
false, &tmp);
x509_parse_signature_algo(ctx, &tmp);
asn1_extract(ctx, &cert, ASN1_UNIV | ASN1_BTS, false, &tmp);
if (!asn1_check_end(ctx, &cert))
return;
/* Remove the bit string's initial unused bit count */
if (tmp.len < 1) {
pr_debug("ASN.1 short BIT STRING @%u+%u\n", tmp.start, tmp.len);
ctx->error = -EBADMSG;
return;
}
tmp.start++;
tmp.len--;
pr_debug("Signature size %u\n", tmp.len);
ctx->cert->sig = ctx->data + tmp.start;
ctx->cert->sig_size = tmp.len;
}
/*
* Parse an X.509 certificate
*/
struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
{
struct x509_certificate *cert;
struct x509_parse_context *ctx;
long ret;
ret = -ENOMEM;
cert = kzalloc(sizeof(struct x509_certificate), GFP_KERNEL);
if (!cert)
goto error_no_cert;
cert->pub = kzalloc(sizeof(struct public_key), GFP_KERNEL);
if (!cert->pub)
goto error_no_ctx;
ctx = kzalloc(sizeof(struct x509_parse_context), GFP_KERNEL);
if (!ctx)
goto error_no_ctx;
ctx->cert = cert;
ctx->data = data;
/* Attempt to decode the certificate */
x509_parse_basic(ctx, datalen);
ret = ctx->error;
if (ret < 0)
goto error_decode;
kfree(ctx);
return cert;
error_decode:
kfree(ctx);
error_no_ctx:
x509_free_certificate(cert);
error_no_cert:
return ERR_PTR(ret);
}
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