Signature verification routines for DSA crypto key subtype.
Signed-off-by: David Howells <dhowe...@redhat.com>
---
security/keys/Makefile | 2
security/keys/crypto_dsa.h | 11 +
security/keys/crypto_dsa_verify.c | 384 +++++++++++++++++++++++++++++++++++++
3 files changed, 396 insertions(+), 1 deletions(-)
create mode 100644 security/keys/crypto_dsa_verify.c
diff --git a/security/keys/Makefile b/security/keys/Makefile
index 8f48527..bde336e 100644
--- a/security/keys/Makefile
+++ b/security/keys/Makefile
@@ -23,5 +23,5 @@ obj-$(CONFIG_PROC_FS) += proc.o
obj-$(CONFIG_SYSCTL) += sysctl.o
crypto_keys-y := crypto_type.o pgp_parse.o crypto_verify.o
-crypto_dsa-y := crypto_dsa_subtype.o
+crypto_dsa-y := crypto_dsa_subtype.o crypto_dsa_verify.o
crypto_rsa-y := crypto_rsa_subtype.o
diff --git a/security/keys/crypto_dsa.h b/security/keys/crypto_dsa.h
index 0455634..8c7c6e9 100644
--- a/security/keys/crypto_dsa.h
+++ b/security/keys/crypto_dsa.h
@@ -34,3 +34,14 @@ struct DSA_payload {
u8 key_id_size; /* Number of bytes in key_id */
struct DSA_public_key *public_key;
};
+
+/*
+ * crypto_dsa_verify.c
+ */
+extern struct crypto_key_verify_context *DSA_verify_sig_begin(
+ struct key *key, const u8 *sig, size_t siglen);
+extern int DSA_verify_sig_add_data(struct crypto_key_verify_context *ctx,
+ const void *data, size_t datalen);
+extern int DSA_verify_sig_end(struct crypto_key_verify_context *ctx,
+ const u8 *sig, size_t siglen);
+extern void DSA_verify_sig_cancel(struct crypto_key_verify_context *ctx);
diff --git a/security/keys/crypto_dsa_verify.c
b/security/keys/crypto_dsa_verify.c
new file mode 100644
index 0000000..c9dc180
--- /dev/null
+++ b/security/keys/crypto_dsa_verify.c
@@ -0,0 +1,384 @@
+/* DSA signature verification algorithm
+ *
+ * Copyright (C) 2011 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 DEBUG
+#define pr_fmt(fmt) "DSA: "fmt
+#include <keys/crypto-subtype.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/mpi.h>
+#include <linux/pgp.h>
+#include <crypto/hash.h>
+#include "internal.h"
+#include "crypto_dsa.h"
+
+#define DSA_NSIG 2 /* number of MPI's in DSA signature */
+
+struct DSA_signature {
+ struct crypto_key_verify_context base;
+ enum pgp_hash_algo hash_algo : 8;
+ u8 signed_hash_msw[2];
+ union {
+ MPI mpi[2];
+ struct {
+ MPI r;
+ MPI s;
+ };
+ };
+ struct shash_desc hash; /* This must go last! */
+};
+
+struct DSA_sig_parse_context {
+ struct pgp_parse_context pgp;
+ struct pgp_sig_parameters params;
+};
+
+static int DSA_parse_signature(struct pgp_parse_context *context,
+ enum pgp_packet_tag type,
+ u8 headerlen,
+ const u8 *data,
+ size_t datalen)
+{
+ struct DSA_sig_parse_context *ctx =
+ container_of(context, struct DSA_sig_parse_context, pgp);
+
+ return pgp_parse_sig_params(&data, &datalen, &ctx->params);
+}
+
+/*
+ * Begin the process of verifying a DSA signature.
+ *
+ * This involves allocating the hash into which first the data and then the
+ * metadata will be put, and parsing the signature to check that it matches the
+ * key.
+ */
+struct crypto_key_verify_context *DSA_verify_sig_begin(
+ struct key *key, const u8 *sigdata, size_t siglen)
+{
+ struct DSA_sig_parse_context p;
+ struct DSA_signature *sig;
+ struct crypto_shash *tfm;
+ struct DSA_payload *dsa = key->payload.data;
+ int ret;
+
+ kenter("{%d},,%zu", key_serial(key), siglen);
+
+ if (!dsa->public_key) {
+ kleave(" = -ENOKEY [no public key]");
+ return ERR_PTR(-ENOKEY);
+ }
+
+ p.pgp.types_of_interest = (1 << PGP_PKT_SIGNATURE);
+ p.pgp.process_packet = DSA_parse_signature;
+ ret = pgp_parse_packets(sigdata, siglen, &p.pgp);
+ if (ret < 0)
+ return ERR_PTR(ret);
+
+ if (p.params.pubkey_algo != PGP_PUBKEY_DSA) {
+ kleave(" = -ENOKEY [wrong pk algo]");
+ return ERR_PTR(-ENOKEY);
+ }
+
+ if (p.params.hash_algo >= PGP_HASH__LAST ||
+ !pgp_hash_algorithms[p.params.hash_algo]) {
+ kleave(" = -ENOPKG [hash]");
+ return ERR_PTR(-ENOPKG);
+ }
+
+ pr_notice("Signature generated with %s hash\n",
+ pgp_hash_algorithms[p.params.hash_algo]);
+
+ if (memcmp(&p.params.issuer, dsa->key_id, 8) != 0) {
+ kleave(" = -ENOKEY [wrong key ID]");
+ return ERR_PTR(-ENOKEY);
+ }
+
+ if (p.params.signature_type != PGP_SIG_BINARY_DOCUMENT_SIG &&
+ p.params.signature_type != PGP_SIG_STANDALONE_SIG) {
+ /* We don't want to canonicalise */
+ kleave(" = -EOPNOTSUPP [canon]");
+ return ERR_PTR(-EOPNOTSUPP);
+ }
+
+ /* Allocate the hashing algorithm we're going to need and find out how
+ * big the hash operational data will be.
+ */
+ tfm = crypto_alloc_shash(pgp_hash_algorithms[p.params.hash_algo], 0, 0);
+ if (IS_ERR(tfm))
+ return PTR_ERR(tfm) == -ENOENT ?
+ ERR_PTR(-ENOPKG) : ERR_CAST(tfm);
+
+ /* We allocate the hash operational data storage on the end of our
+ * context data.
+ */
+ sig = kzalloc(sizeof(*sig) + crypto_shash_descsize(tfm), GFP_KERNEL);
+ if (!sig) {
+ crypto_free_shash(tfm);
+ return ERR_PTR(-ENOMEM);
+ }
+
+ sig->base.key = key;
+ sig->hash_algo = p.params.hash_algo;
+ sig->hash.tfm = tfm;
+ sig->hash.flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+
+ ret = crypto_shash_init(&sig->hash);
+ if (ret < 0) {
+ crypto_free_shash(sig->hash.tfm);
+ kfree(sig);
+ return ERR_PTR(ret);
+ }
+
+ key_get(sig->base.key);
+ kleave(" = %p", sig);
+ return &sig->base;
+}
+
+/*
+ * Load data into the hash
+ */
+int DSA_verify_sig_add_data(struct crypto_key_verify_context *ctx,
+ const void *data, size_t datalen)
+{
+ struct DSA_signature *sig =
+ container_of(ctx, struct DSA_signature, base);
+
+ return crypto_shash_update(&sig->hash, data, datalen);
+}
+
+/*
+ * Perform the actual mathematical DSA signature verification.
+ */
+static int DSA_verify(const MPI datahash,
+ const struct DSA_signature *sig,
+ const struct DSA_public_key *pub)
+{
+ MPI w = NULL, u1 = NULL, u2 = NULL, v = NULL;
+ MPI base[3];
+ MPI exp[3];
+ int rc;
+
+ kenter("");
+
+ if (!(mpi_cmp_ui(sig->r, 0) > 0 && mpi_cmp(sig->r, pub->q) < 0)) {
+ pr_warning("Assertion failed [0 < r < q]\n");
+ return -EKEYREJECTED;
+ }
+
+ if (!(mpi_cmp_ui(sig->s, 0) > 0 && mpi_cmp(sig->s, pub->q) < 0)) {
+ pr_warning("Assertion failed [0 < s < q]\n");
+ return -EKEYREJECTED;
+ }
+
+ rc = -ENOMEM;
+ w = mpi_alloc(mpi_get_nlimbs(pub->q)); if (!w ) goto cleanup;
+ u1 = mpi_alloc(mpi_get_nlimbs(pub->q)); if (!u1) goto cleanup;
+ u2 = mpi_alloc(mpi_get_nlimbs(pub->q)); if (!u2) goto cleanup;
+ v = mpi_alloc(mpi_get_nlimbs(pub->p)); if (!v ) goto cleanup;
+
+ /* w = s^(-1) mod q */
+ if (mpi_invm(w, sig->s, pub->q) < 0)
+ goto cleanup;
+
+ /* u1 = (datahash * w) mod q */
+ if (mpi_mulm(u1, datahash, w, pub->q) < 0)
+ goto cleanup;
+
+ /* u2 = r * w mod q */
+ if (mpi_mulm(u2, sig->r, w, pub->q) < 0)
+ goto cleanup;
+
+ /* v = g^u1 * y^u2 mod p mod q */
+ base[0] = pub->g; exp[0] = u1;
+ base[1] = pub->y; exp[1] = u2;
+ base[2] = NULL; exp[2] = NULL;
+
+ if (mpi_mulpowm(v, base, exp, pub->p) < 0)
+ goto cleanup;
+
+ if (mpi_fdiv_r(v, v, pub->q) < 0)
+ goto cleanup;
+
+ rc = (mpi_cmp(v, sig->r) == 0) ? 0 : -EKEYREJECTED;
+
+cleanup:
+ mpi_free(w);
+ mpi_free(u1);
+ mpi_free(u2);
+ mpi_free(v);
+ kleave(" = %d", rc);
+ return rc;
+}
+
+struct DSA_sig_digest_context {
+ struct pgp_parse_context pgp;
+ struct DSA_signature *sig;
+};
+
+/*
+ * Extract required metadata from the signature packet and add what we need to
+ * to the hash.
+ */
+static int DSA_digest_signature(struct pgp_parse_context *context,
+ enum pgp_packet_tag type,
+ u8 headerlen,
+ const u8 *data,
+ size_t datalen)
+{
+ enum pgp_signature_version version;
+ struct DSA_sig_digest_context *ctx =
+ container_of(context, struct DSA_sig_digest_context, pgp);
+ int i;
+
+ kenter("");
+
+ version = *data;
+ if (version == PGP_SIG_VERSION_3) {
+ /* We just include an excerpt of the metadata from a V3
+ * signature.
+ */
+ crypto_shash_update(&ctx->sig->hash, data + 1, 5);
+ data += sizeof(struct pgp_signature_v3_packet);
+ datalen -= sizeof(struct pgp_signature_v3_packet);
+ } else if (version == PGP_SIG_VERSION_4) {
+ /* We add the whole metadata header and some of the hashed data
+ * for a V4 signature, plus a trailer.
+ */
+ size_t hashedsz, unhashedsz;
+ u8 trailer[6];
+
+ hashedsz = 4 + 2 + (data[4] << 8) + data[5];
+ crypto_shash_update(&ctx->sig->hash, data, hashedsz);
+
+ trailer[0] = version;
+ trailer[1] = 0xffU;
+ trailer[2] = hashedsz >> 24;
+ trailer[3] = hashedsz >> 16;
+ trailer[4] = hashedsz >> 8;
+ trailer[5] = hashedsz;
+
+ crypto_shash_update(&ctx->sig->hash, trailer, 6);
+ data += hashedsz;
+ datalen -= hashedsz;
+
+ unhashedsz = 2 + (data[0] << 8) + data[1];
+ data += unhashedsz;
+ datalen -= unhashedsz;
+ }
+
+ if (datalen <= 2) {
+ kleave(" = -EBADMSG");
+ return -EBADMSG;
+ }
+
+ /* There's a quick check on the hash available. */
+ ctx->sig->signed_hash_msw[0] = *data++;
+ ctx->sig->signed_hash_msw[1] = *data++;
+ datalen -= 2;
+
+ /* And then the cryptographic data, which we'll need for the
+ * algorithm.
+ */
+ for (i = 0; i < DSA_NSIG; i++) {
+ unsigned int remaining = datalen;
+ ctx->sig->mpi[i] = mpi_read_from_buffer(data, &remaining);
+ if (!ctx->sig->mpi[i])
+ return -ENOMEM;
+ data += remaining;
+ datalen -= remaining;
+ }
+
+ if (datalen != 0) {
+ kleave(" = -EBADMSG [trailer %zu]", datalen);
+ return -EBADMSG;
+ }
+
+ kleave(" = 0");
+ return 0;
+}
+
+/*
+ * The data is now all loaded into the hash; load the metadata, finalise the
+ * hash and perform the verification step.
+ */
+int DSA_verify_sig_end(struct crypto_key_verify_context *ctx,
+ const u8 *sigdata, size_t siglen)
+{
+ struct DSA_signature *sig =
+ container_of(ctx, struct DSA_signature, base);
+ struct DSA_payload *dsa = sig->base.key->payload.data;
+ struct DSA_sig_digest_context p;
+ void *digest = NULL;
+ MPI datahash = NULL;
+ size_t digest_size;
+ int ret;
+
+ kenter("");
+
+ /* Firstly we add metadata, starting with some of the data from the
+ * signature packet */
+ p.pgp.types_of_interest = (1 << PGP_PKT_SIGNATURE);
+ p.pgp.process_packet = DSA_digest_signature;
+ p.sig = sig;
+ ret = pgp_parse_packets(sigdata, siglen, &p.pgp);
+ if (ret < 0)
+ goto error_free_ctx;
+
+ ret = -ENOMEM;
+ digest_size = crypto_shash_digestsize(sig->hash.tfm);
+ digest = kmalloc(digest_size, GFP_KERNEL);
+ if (!digest)
+ goto error_free_ctx;
+
+ crypto_shash_final(&sig->hash, digest);
+
+ ret = -ENOMEM;
+ datahash = mpi_alloc((digest_size + BYTES_PER_MPI_LIMB - 1) /
+ BYTES_PER_MPI_LIMB);
+ if (!datahash)
+ goto error_free_digest;
+
+ ret = mpi_set_buffer(datahash, digest, digest_size, 0);
+ if (ret < 0)
+ goto error_free_mpi;
+
+ ret = DSA_verify(datahash, sig, dsa->public_key);
+
+error_free_mpi:
+ mpi_free(datahash);
+error_free_digest:
+ kfree(digest);
+error_free_ctx:
+ DSA_verify_sig_cancel(ctx);
+ kleave(" = %d", ret);
+ return ret;
+}
+
+/*
+ * Cancel an in-progress data loading
+ */
+void DSA_verify_sig_cancel(struct crypto_key_verify_context *_ctx)
+{
+ struct DSA_signature *sig =
+ container_of(_ctx, struct DSA_signature, base);
+
+ kenter("");
+
+ /* !!! Do we need to tell the crypto layer to cancel too? */
+ crypto_free_shash(sig->hash.tfm);
+ key_put(sig->base.key);
+ mpi_free(sig->r);
+ mpi_free(sig->s);
+ kfree(sig);
+
+ kleave("");
+}
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