--- /dev/null
+From 511563ce763b1e98e3fb3b3e3addfef550ff99b2 Mon Sep 17 00:00:00 2001
+From: Tobias Brunner <tobias@strongswan.org>
+Date: Tue, 28 Aug 2018 11:26:24 +0200
+Subject: [PATCH] gmp: Don't parse PKCS1 v1.5 RSA signatures to verify them
+
+Instead we generate the expected signature encoding and compare it to the
+decrypted value.
+
+Due to the lenient nature of the previous parsing code (minimum padding
+length was not enforced, the algorithmIdentifier/OID parser accepts arbitrary
+data after OIDs and in the parameters field etc.) it was susceptible to
+Daniel Bleichenbacher's low-exponent attack (from 2006!), which allowed
+forging signatures for keys that use low public exponents (i.e. e=3).
+
+Since the public exponent is usually set to 0x10001 (65537) since quite a
+while, the flaws in the previous code should not have had that much of a
+practical impact in recent years.
+
+Fixes: CVE-2018-16151, CVE-2018-16152
+---
+ .../plugins/gmp/gmp_rsa_private_key.c | 66 +++++----
+ src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c | 156 ++-------------------
+ 2 files changed, 52 insertions(+), 170 deletions(-)
+
+diff --git a/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c b/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c
+index 241ef7d3b12b..edc178e96a4f 100644
+--- a/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c
++++ b/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c
+@@ -264,14 +264,15 @@ static chunk_t rsasp1(private_gmp_rsa_private_key_t *this, chunk_t data)
+ }
+
+ /**
+- * Build a signature using the PKCS#1 EMSA scheme
++ * Hashes the data and builds the plaintext signature value with EMSA
++ * PKCS#1 v1.5 padding.
++ *
++ * Allocates the signature data.
+ */
+-static bool build_emsa_pkcs1_signature(private_gmp_rsa_private_key_t *this,
+- hash_algorithm_t hash_algorithm,
+- chunk_t data, chunk_t *signature)
++bool gmp_emsa_pkcs1_signature_data(hash_algorithm_t hash_algorithm,
++ chunk_t data, size_t keylen, chunk_t *em)
+ {
+ chunk_t digestInfo = chunk_empty;
+- chunk_t em;
+
+ if (hash_algorithm != HASH_UNKNOWN)
+ {
+@@ -295,43 +296,56 @@ static bool build_emsa_pkcs1_signature(private_gmp_rsa_private_key_t *this,
+ /* build DER-encoded digestInfo */
+ digestInfo = asn1_wrap(ASN1_SEQUENCE, "mm",
+ asn1_algorithmIdentifier(hash_oid),
+- asn1_simple_object(ASN1_OCTET_STRING, hash)
+- );
+- chunk_free(&hash);
++ asn1_wrap(ASN1_OCTET_STRING, "m", hash));
++
+ data = digestInfo;
+ }
+
+- if (data.len > this->k - 3)
++ if (data.len > keylen - 11)
+ {
+- free(digestInfo.ptr);
+- DBG1(DBG_LIB, "unable to sign %d bytes using a %dbit key", data.len,
+- mpz_sizeinbase(this->n, 2));
++ chunk_free(&digestInfo);
++ DBG1(DBG_LIB, "signature value of %zu bytes is too long for key of "
++ "%zu bytes", data.len, keylen);
+ return FALSE;
+ }
+
+- /* build chunk to rsa-decrypt:
+- * EM = 0x00 || 0x01 || PS || 0x00 || T.
+- * PS = 0xFF padding, with length to fill em
++ /* EM = 0x00 || 0x01 || PS || 0x00 || T.
++ * PS = 0xFF padding, with length to fill em (at least 8 bytes)
+ * T = encoded_hash
+ */
+- em.len = this->k;
+- em.ptr = malloc(em.len);
++ *em = chunk_alloc(keylen);
+
+ /* fill em with padding */
+- memset(em.ptr, 0xFF, em.len);
++ memset(em->ptr, 0xFF, em->len);
+ /* set magic bytes */
+- *(em.ptr) = 0x00;
+- *(em.ptr+1) = 0x01;
+- *(em.ptr + em.len - data.len - 1) = 0x00;
+- /* set DER-encoded hash */
+- memcpy(em.ptr + em.len - data.len, data.ptr, data.len);
++ *(em->ptr) = 0x00;
++ *(em->ptr+1) = 0x01;
++ *(em->ptr + em->len - data.len - 1) = 0x00;
++ /* set encoded hash */
++ memcpy(em->ptr + em->len - data.len, data.ptr, data.len);
++
++ chunk_clear(&digestInfo);
++ return TRUE;
++}
++
++/**
++ * Build a signature using the PKCS#1 EMSA scheme
++ */
++static bool build_emsa_pkcs1_signature(private_gmp_rsa_private_key_t *this,
++ hash_algorithm_t hash_algorithm,
++ chunk_t data, chunk_t *signature)
++{
++ chunk_t em;
++
++ if (!gmp_emsa_pkcs1_signature_data(hash_algorithm, data, this->k, &em))
++ {
++ return FALSE;
++ }
+
+ /* build signature */
+ *signature = rsasp1(this, em);
+
+- free(digestInfo.ptr);
+- free(em.ptr);
+-
++ chunk_free(&em);
+ return TRUE;
+ }
+
+diff --git a/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c b/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c
+index 52bc9fb38046..ce9a80fadf2a 100644
+--- a/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c
++++ b/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c
+@@ -70,7 +70,9 @@ struct private_gmp_rsa_public_key_t {
+ /**
+ * Shared functions defined in gmp_rsa_private_key.c
+ */
+-extern chunk_t gmp_mpz_to_chunk(const mpz_t value);
++chunk_t gmp_mpz_to_chunk(const mpz_t value);
++bool gmp_emsa_pkcs1_signature_data(hash_algorithm_t hash_algorithm,
++ chunk_t data, size_t keylen, chunk_t *em);
+
+ /**
+ * RSAEP algorithm specified in PKCS#1.
+@@ -115,26 +117,13 @@ static chunk_t rsavp1(private_gmp_rsa_public_key_t *this, chunk_t data)
+ }
+
+ /**
+- * ASN.1 definition of digestInfo
+- */
+-static const asn1Object_t digestInfoObjects[] = {
+- { 0, "digestInfo", ASN1_SEQUENCE, ASN1_OBJ }, /* 0 */
+- { 1, "digestAlgorithm", ASN1_EOC, ASN1_RAW }, /* 1 */
+- { 1, "digest", ASN1_OCTET_STRING, ASN1_BODY }, /* 2 */
+- { 0, "exit", ASN1_EOC, ASN1_EXIT }
+-};
+-#define DIGEST_INFO 0
+-#define DIGEST_INFO_ALGORITHM 1
+-#define DIGEST_INFO_DIGEST 2
+-
+-/**
+ * Verification of an EMSA PKCS1 signature described in PKCS#1
+ */
+ static bool verify_emsa_pkcs1_signature(private_gmp_rsa_public_key_t *this,
+ hash_algorithm_t algorithm,
+ chunk_t data, chunk_t signature)
+ {
+- chunk_t em_ori, em;
++ chunk_t em_expected, em;
+ bool success = FALSE;
+
+ /* remove any preceding 0-bytes from signature */
+@@ -148,140 +137,19 @@ static bool verify_emsa_pkcs1_signature(private_gmp_rsa_public_key_t *this,
+ return FALSE;
+ }
+
+- /* unpack signature */
+- em_ori = em = rsavp1(this, signature);
+-
+- /* result should look like this:
+- * EM = 0x00 || 0x01 || PS || 0x00 || T.
+- * PS = 0xFF padding, with length to fill em
+- * T = oid || hash
+- */
+-
+- /* check magic bytes */
+- if (em.len < 2 || *(em.ptr) != 0x00 || *(em.ptr+1) != 0x01)
++ /* generate expected signature value */
++ if (!gmp_emsa_pkcs1_signature_data(algorithm, data, this->k, &em_expected))
+ {
+- goto end;
+- }
+- em = chunk_skip(em, 2);
+-
+- /* find magic 0x00 */
+- while (em.len > 0)
+- {
+- if (*em.ptr == 0x00)
+- {
+- /* found magic byte, stop */
+- em = chunk_skip(em, 1);
+- break;
+- }
+- else if (*em.ptr != 0xFF)
+- {
+- /* bad padding, decryption failed ?!*/
+- goto end;
+- }
+- em = chunk_skip(em, 1);
+- }
+-
+- if (em.len == 0)
+- {
+- /* no digestInfo found */
+- goto end;
+- }
+-
+- if (algorithm == HASH_UNKNOWN)
+- { /* IKEv1 signatures without digestInfo */
+- if (em.len != data.len)
+- {
+- DBG1(DBG_LIB, "hash size in signature is %u bytes instead of"
+- " %u bytes", em.len, data.len);
+- goto end;
+- }
+- success = memeq_const(em.ptr, data.ptr, data.len);
++ return FALSE;
+ }
+- else
+- { /* IKEv2 and X.509 certificate signatures */
+- asn1_parser_t *parser;
+- chunk_t object;
+- int objectID;
+- hash_algorithm_t hash_algorithm = HASH_UNKNOWN;
+-
+- DBG2(DBG_LIB, "signature verification:");
+- parser = asn1_parser_create(digestInfoObjects, em);
+
+- while (parser->iterate(parser, &objectID, &object))
+- {
+- switch (objectID)
+- {
+- case DIGEST_INFO:
+- {
+- if (em.len > object.len)
+- {
+- DBG1(DBG_LIB, "digestInfo field in signature is"
+- " followed by %u surplus bytes",
+- em.len - object.len);
+- goto end_parser;
+- }
+- break;
+- }
+- case DIGEST_INFO_ALGORITHM:
+- {
+- int hash_oid = asn1_parse_algorithmIdentifier(object,
+- parser->get_level(parser)+1, NULL);
+-
+- hash_algorithm = hasher_algorithm_from_oid(hash_oid);
+- if (hash_algorithm == HASH_UNKNOWN || hash_algorithm != algorithm)
+- {
+- DBG1(DBG_LIB, "expected hash algorithm %N, but found"
+- " %N (OID: %#B)", hash_algorithm_names, algorithm,
+- hash_algorithm_names, hash_algorithm, &object);
+- goto end_parser;
+- }
+- break;
+- }
+- case DIGEST_INFO_DIGEST:
+- {
+- chunk_t hash;
+- hasher_t *hasher;
+-
+- hasher = lib->crypto->create_hasher(lib->crypto, hash_algorithm);
+- if (hasher == NULL)
+- {
+- DBG1(DBG_LIB, "hash algorithm %N not supported",
+- hash_algorithm_names, hash_algorithm);
+- goto end_parser;
+- }
+-
+- if (object.len != hasher->get_hash_size(hasher))
+- {
+- DBG1(DBG_LIB, "hash size in signature is %u bytes"
+- " instead of %u bytes", object.len,
+- hasher->get_hash_size(hasher));
+- hasher->destroy(hasher);
+- goto end_parser;
+- }
+-
+- /* build our own hash and compare */
+- if (!hasher->allocate_hash(hasher, data, &hash))
+- {
+- hasher->destroy(hasher);
+- goto end_parser;
+- }
+- hasher->destroy(hasher);
+- success = memeq_const(object.ptr, hash.ptr, hash.len);
+- free(hash.ptr);
+- break;
+- }
+- default:
+- break;
+- }
+- }
++ /* unpack signature */
++ em = rsavp1(this, signature);
+
+-end_parser:
+- success &= parser->success(parser);
+- parser->destroy(parser);
+- }
++ success = chunk_equals_const(em_expected, em);
+
+-end:
+- free(em_ori.ptr);
++ chunk_free(&em_expected);
++ chunk_free(&em);
+ return success;
+ }
+
+--
+2.7.4
+
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