[RFC 6/8] KEYS: PGP data parser
From: Petr Tesarik
Date: Fri Feb 16 2024 - 10:35:45 EST
From: David Howells <dhowells@xxxxxxxxxx>
Implement a PGP data parser for the crypto key type to use when
instantiating a key.
This parser attempts to parse the instantiation data as a PGP packet
sequence (RFC 4880) and if it parses okay, attempts to extract a public-key
algorithm key or subkey from it.
If it finds such a key, it will set up a public_key subtype payload with
appropriate handler routines (RSA) and attach it to the key.
Thanks to Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> for pointing
out some errors.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Co-developed-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
crypto/asymmetric_keys/Kconfig | 11 +
crypto/asymmetric_keys/Makefile | 4 +
crypto/asymmetric_keys/pgp_parser.h | 18 +
crypto/asymmetric_keys/pgp_public_key.c | 416 ++++++++++++++++++++++++
4 files changed, 449 insertions(+)
create mode 100644 crypto/asymmetric_keys/pgp_parser.h
create mode 100644 crypto/asymmetric_keys/pgp_public_key.c
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index ebe9dc88d975..ebde5ef5d65f 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -92,4 +92,15 @@ config PGP_LIBRARY
This option enables a library that provides a number of simple
utility functions for parsing PGP (RFC 4880) packet-based messages.
+config PGP_KEY_PARSER
+ tristate "PGP key parser"
+ depends on ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+ select PGP_LIBRARY
+ select MD5 # V3 fingerprint generation
+ select SHA1 # V4 fingerprint generation
+ help
+ This option provides support for parsing PGP (RFC 4880) format blobs
+ for key data and provides the ability to instantiate a crypto key
+ from a public key packet found inside the blob.
+
endif # ASYMMETRIC_KEY_TYPE
diff --git a/crypto/asymmetric_keys/Makefile b/crypto/asymmetric_keys/Makefile
index f7e5ee59857f..36a27cf2daff 100644
--- a/crypto/asymmetric_keys/Makefile
+++ b/crypto/asymmetric_keys/Makefile
@@ -93,3 +93,7 @@ $(obj)/tpm.asn1.o: $(obj)/tpm.asn1.c $(obj)/tpm.asn1.h
# PGP handling
#
obj-$(CONFIG_PGP_LIBRARY) += pgp_library.o
+
+obj-$(CONFIG_PGP_KEY_PARSER) += pgp_key_parser.o
+pgp_key_parser-y := \
+ pgp_public_key.o
diff --git a/crypto/asymmetric_keys/pgp_parser.h b/crypto/asymmetric_keys/pgp_parser.h
new file mode 100644
index 000000000000..1a560ce32415
--- /dev/null
+++ b/crypto/asymmetric_keys/pgp_parser.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* PGP crypto data parser internal definitions
+ *
+ * Copyright (C) 2011 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@xxxxxxxxxx)
+ */
+
+#include "pgplib.h"
+
+#define kenter(FMT, ...) \
+ pr_devel("==> %s("FMT")\n", __func__, ##__VA_ARGS__)
+#define kleave(FMT, ...) \
+ pr_devel("<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
+
+/*
+ * pgp_public_key.c
+ */
+extern const char *pgp_to_public_key_algo[PGP_PUBKEY__LAST];
diff --git a/crypto/asymmetric_keys/pgp_public_key.c b/crypto/asymmetric_keys/pgp_public_key.c
new file mode 100644
index 000000000000..0529c8ce2d43
--- /dev/null
+++ b/crypto/asymmetric_keys/pgp_public_key.c
@@ -0,0 +1,416 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Instantiate a public key crypto key from PGP format data [RFC 4880]
+ *
+ * Copyright (C) 2011 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@xxxxxxxxxx)
+ */
+
+#define pr_fmt(fmt) "PGP: "fmt
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/mpi.h>
+#include <keys/asymmetric-subtype.h>
+#include <keys/asymmetric-parser.h>
+#include <crypto/hash.h>
+#include <crypto/public_key.h>
+
+#include "pgp_parser.h"
+
+#define MAX_MPI 5
+#define KEYCTL_SUPPORTS_ENCDEC \
+ (KEYCTL_SUPPORTS_ENCRYPT | KEYCTL_SUPPORTS_DECRYPT)
+#define KEYCTL_SUPPORTS_SIGVER (KEYCTL_SUPPORTS_SIGN | KEYCTL_SUPPORTS_VERIFY)
+
+MODULE_LICENSE("GPL");
+
+const char *pgp_to_public_key_algo[PGP_PUBKEY__LAST] = {
+ [PGP_PUBKEY_RSA_ENC_OR_SIG] = "rsa",
+ [PGP_PUBKEY_RSA_ENC_ONLY] = "rsa",
+ [PGP_PUBKEY_RSA_SIG_ONLY] = "rsa",
+ [PGP_PUBKEY_ELGAMAL] = NULL,
+ [PGP_PUBKEY_DSA] = NULL,
+};
+
+static const int pgp_key_algo_p_num_mpi[PGP_PUBKEY__LAST] = {
+ [PGP_PUBKEY_RSA_ENC_OR_SIG] = 2,
+ [PGP_PUBKEY_RSA_ENC_ONLY] = 2,
+ [PGP_PUBKEY_RSA_SIG_ONLY] = 2,
+ [PGP_PUBKEY_ELGAMAL] = 3,
+ [PGP_PUBKEY_DSA] = 4,
+};
+
+static const u8 pgp_public_key_capabilities[PGP_PUBKEY__LAST] = {
+ [PGP_PUBKEY_RSA_ENC_OR_SIG] = KEYCTL_SUPPORTS_ENCDEC |
+ KEYCTL_SUPPORTS_SIGVER,
+ [PGP_PUBKEY_RSA_ENC_ONLY] = KEYCTL_SUPPORTS_ENCDEC,
+ [PGP_PUBKEY_RSA_SIG_ONLY] = KEYCTL_SUPPORTS_SIGVER,
+ [PGP_PUBKEY_ELGAMAL] = 0,
+ [PGP_PUBKEY_DSA] = 0,
+};
+
+struct pgp_key_data_parse_context {
+ struct pgp_parse_context pgp;
+ u8 key[1024];
+ size_t keylen;
+ u8 keyid_buf[1024];
+ size_t keyid_buf_len;
+ char user_id[512];
+ size_t user_id_len;
+ const char *algo;
+ u8 raw_fingerprint[HASH_MAX_DIGESTSIZE];
+ size_t raw_fingerprint_len;
+ unsigned int version;
+};
+
+static inline void write_keyid_buf_char(struct pgp_key_data_parse_context *ctx,
+ uint8_t ch)
+{
+ memcpy(&ctx->keyid_buf[ctx->keyid_buf_len++], &ch, 1);
+}
+
+/*
+ * Build buffer to calculate the public key ID (RFC4880 12.2)
+ */
+static int pgp_build_pkey_keyid_buf(struct pgp_key_data_parse_context *ctx,
+ struct pgp_parse_pubkey *pgp)
+{
+ unsigned int nb[MAX_MPI];
+ unsigned int nn[MAX_MPI];
+ unsigned int n;
+ size_t keylen = ctx->keylen;
+ u8 *key_ptr = ctx->key;
+ u8 *pp[MAX_MPI];
+ u32 a32;
+ int npkey = pgp_key_algo_p_num_mpi[pgp->pubkey_algo];
+ int i, ret;
+
+ kenter("");
+
+ n = (pgp->version < PGP_KEY_VERSION_4) ? 8 : 6;
+ for (i = 0; i < npkey; i++) {
+ ret = mpi_key_length(key_ptr, keylen, nb + i, nn + i);
+ if (ret < 0) {
+ kleave(" = %d", ret);
+ return ret;
+ }
+
+ if (keylen < 2 + nn[i])
+ break;
+
+ pp[i] = key_ptr + 2;
+ key_ptr += 2 + nn[i];
+ keylen -= 2 + nn[i];
+ n += 2 + nn[i];
+ }
+
+ if (keylen != 0) {
+ pr_debug("excess %zu\n", keylen);
+ kleave(" = -EBADMSG");
+ return -EBADMSG;
+ }
+
+ write_keyid_buf_char(ctx, 0x99); /* ctb */
+ write_keyid_buf_char(ctx, n >> 8); /* 16-bit header length */
+ write_keyid_buf_char(ctx, n);
+
+ write_keyid_buf_char(ctx, pgp->version);
+
+ a32 = pgp->creation_time;
+ write_keyid_buf_char(ctx, a32 >> 24);
+ write_keyid_buf_char(ctx, a32 >> 16);
+ write_keyid_buf_char(ctx, a32 >> 8);
+ write_keyid_buf_char(ctx, a32 >> 0);
+
+ if (pgp->version < PGP_KEY_VERSION_4) {
+ u16 a16;
+
+ if (pgp->expires_at)
+ a16 = (pgp->expires_at - pgp->creation_time) / 86400UL;
+ else
+ a16 = 0;
+ write_keyid_buf_char(ctx, a16 >> 8);
+ write_keyid_buf_char(ctx, a16 >> 0);
+ }
+
+ write_keyid_buf_char(ctx, pgp->pubkey_algo);
+
+ for (i = 0; i < npkey; i++) {
+ write_keyid_buf_char(ctx, nb[i] >> 8);
+ write_keyid_buf_char(ctx, nb[i]);
+ memcpy(&ctx->keyid_buf[ctx->keyid_buf_len], pp[i], nn[i]);
+ ctx->keyid_buf_len += nn[i];
+ }
+
+ kleave(" = 0");
+ return 0;
+}
+
+/*
+ * Extract a public key or public subkey from the PGP stream.
+ */
+static int pgp_process_public_key(struct pgp_parse_context *context,
+ enum pgp_packet_tag type,
+ u8 headerlen,
+ const u8 *data,
+ size_t datalen)
+{
+ struct pgp_key_data_parse_context *ctx =
+ container_of(context, struct pgp_key_data_parse_context, pgp);
+ struct pgp_parse_pubkey pgp;
+ u8 capabilities;
+ int ret;
+
+ kenter(",%u,%u,,%zu", type, headerlen, datalen);
+
+ if (type == PGP_PKT_USER_ID) {
+ if (!ctx->user_id_len) {
+ if (ctx->user_id_len > sizeof(ctx->user_id)) {
+ kleave(" = -E2BIG");
+ return -E2BIG;
+ }
+
+ memcpy(ctx->user_id, data, datalen);
+ ctx->user_id_len = datalen;
+ }
+ kleave(" = 0 [user ID]");
+ return 0;
+ }
+
+ if (ctx->keyid_buf_len) {
+ kleave(" = -EBADMSG");
+ return -EBADMSG;
+ }
+
+ ret = pgp_parse_public_key(&data, &datalen, &pgp);
+ if (ret < 0) {
+ kleave(" = %d", ret);
+ return ret;
+ }
+
+ ctx->version = pgp.version;
+
+ if (pgp.pubkey_algo < PGP_PUBKEY__LAST)
+ ctx->algo = pgp_to_public_key_algo[pgp.pubkey_algo];
+
+ if (!ctx->algo) {
+ pr_debug("Unsupported public key algorithm %u\n",
+ pgp.pubkey_algo);
+ kleave(" = -ENOPKG");
+ return -ENOPKG;
+ }
+
+ /*
+ * It's the public half of a key, so that only gives us encrypt and
+ * verify capabilities.
+ */
+ capabilities = pgp_public_key_capabilities[pgp.pubkey_algo] &
+ (KEYCTL_SUPPORTS_ENCRYPT | KEYCTL_SUPPORTS_VERIFY);
+ /*
+ * Capabilities are not stored anymore in the public key, store only
+ * those that allow signature verification.
+ */
+ if (!(capabilities & KEYCTL_SUPPORTS_VERIFY)) {
+ pr_debug("Public key cannot be used for verification\n");
+ kleave(" = -ENOPKG");
+ return -ENOPKG;
+ }
+
+ if (datalen > sizeof(ctx->key)) {
+ kleave(" = -E2BIG");
+ return -E2BIG;
+ }
+
+ memcpy(ctx->key, data, datalen);
+ ctx->keylen = datalen;
+
+ ret = pgp_build_pkey_keyid_buf(ctx, &pgp);
+
+ kleave(" = %d", ret);
+ return ret;
+}
+
+/*
+ * Calculate the public key ID fingerprint
+ */
+static int pgp_generate_fingerprint(struct pgp_key_data_parse_context *ctx)
+{
+ struct crypto_shash *tfm;
+ struct shash_desc *digest;
+ char fingerprint[HASH_MAX_DIGESTSIZE * 2 + 1] = { 0 };
+ size_t offset;
+ int ret;
+
+ ret = -ENOMEM;
+ tfm = crypto_alloc_shash(ctx->version < PGP_KEY_VERSION_4 ?
+ "md5" : "sha1", 0, 0);
+ if (!tfm)
+ goto cleanup;
+
+ digest = kmalloc(sizeof(*digest) + crypto_shash_descsize(tfm),
+ GFP_KERNEL);
+ if (!digest)
+ goto cleanup_tfm;
+
+ digest->tfm = tfm;
+ crypto_shash_set_flags(digest->tfm, CRYPTO_TFM_REQ_MAY_SLEEP);
+ ret = crypto_shash_init(digest);
+ if (ret < 0)
+ goto cleanup_hash;
+
+ crypto_shash_update(digest, ctx->keyid_buf, ctx->keyid_buf_len);
+
+ ctx->raw_fingerprint_len = crypto_shash_digestsize(tfm);
+
+ ret = crypto_shash_final(digest, ctx->raw_fingerprint);
+ if (ret < 0)
+ goto cleanup_hash;
+
+ offset = ctx->raw_fingerprint_len - 8;
+ pr_debug("offset %lu/%lu\n", offset, ctx->raw_fingerprint_len);
+
+ bin2hex(fingerprint, ctx->raw_fingerprint, ctx->raw_fingerprint_len);
+ pr_debug("fingerprint %s\n", fingerprint);
+
+ ret = 0;
+cleanup_hash:
+ kfree(digest);
+cleanup_tfm:
+ crypto_free_shash(tfm);
+cleanup:
+ return ret;
+}
+
+static struct asymmetric_key_ids *pgp_key_generate_id(
+ struct pgp_key_data_parse_context *ctx)
+{
+ struct asymmetric_key_ids *kids;
+ struct asymmetric_key_id *kid;
+
+ kids = kzalloc(sizeof(struct asymmetric_key_ids), GFP_KERNEL);
+ if (!kids)
+ return kids;
+
+ kid = asymmetric_key_generate_id(ctx->raw_fingerprint,
+ ctx->raw_fingerprint_len, NULL, 0);
+ if (IS_ERR(kid))
+ goto error;
+
+ kids->id[0] = kid;
+ kids->id[1] = kmemdup(kid, sizeof(*kid) + ctx->raw_fingerprint_len,
+ GFP_KERNEL);
+ if (!kids->id[1])
+ goto error;
+
+ return kids;
+error:
+ kfree(kids->id[0]);
+ kfree(kids);
+
+ return NULL;
+}
+
+/*
+ * Attempt to parse the instantiation data blob for a key as a PGP packet
+ * message holding a key.
+ */
+static int pgp_key_parse(struct key_preparsed_payload *prep)
+{
+ struct pgp_key_data_parse_context *ctx;
+ struct public_key *pub = NULL;
+ int ret;
+
+ kenter("");
+
+ ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+ if (!ctx) {
+ kleave(" = -ENOMEM");
+ return -ENOMEM;
+ }
+
+ ctx->pgp.types_of_interest = (1 << PGP_PKT_PUBLIC_KEY) |
+ (1 << PGP_PKT_USER_ID);
+ ctx->pgp.process_packet = pgp_process_public_key;
+
+ ret = pgp_parse_packets(prep->data, prep->datalen, &ctx->pgp);
+ if (ret < 0)
+ goto error;
+
+ ret = pgp_generate_fingerprint(ctx);
+ if (ret < 0)
+ goto error;
+
+ pub = kzalloc(sizeof(struct public_key), GFP_KERNEL);
+ if (!pub) {
+ ret = -ENOMEM;
+ goto error;
+ }
+
+ pub->key = kmemdup(ctx->key, ctx->keylen, GFP_KERNEL);
+ if (!pub->key) {
+ ret = -ENOMEM;
+ goto error;
+ }
+
+ pub->keylen = ctx->keylen;
+ pub->id_type = "PGP";
+ pub->pkey_algo = ctx->algo;
+
+ if (ctx->user_id && ctx->user_id_len > 0) {
+ /*
+ * Propose a description for the key (user ID without the
+ * comment).
+ */
+ size_t ulen = ctx->user_id_len;
+
+ if (ulen > 255 - 9)
+ ulen = 255 - 9;
+ prep->description = kmalloc(ulen + 1 + 8 + 1, GFP_KERNEL);
+ ret = -ENOMEM;
+ if (!prep->description)
+ goto error;
+ memcpy(prep->description, ctx->user_id, ulen);
+ prep->description[ulen] = ' ';
+ bin2hex(prep->description + ulen + 1,
+ ctx->raw_fingerprint + ctx->raw_fingerprint_len - 4, 4);
+ prep->description[ulen + 9] = '\0';
+ pr_debug("desc '%s'\n", prep->description);
+ }
+
+ /* We're pinning the module by being linked against it */
+ __module_get(public_key_subtype.owner);
+ prep->payload.data[asym_subtype] = &public_key_subtype;
+ prep->payload.data[asym_key_ids] = pgp_key_generate_id(ctx);
+ prep->payload.data[asym_crypto] = pub;
+ prep->quotalen = 100;
+ kfree(ctx);
+ return 0;
+
+error:
+ public_key_free(pub);
+ kfree(ctx);
+ kleave(" = %d", ret);
+ return ret;
+}
+
+static struct asymmetric_key_parser pgp_key_parser = {
+ .owner = THIS_MODULE,
+ .name = "pgp",
+ .parse = pgp_key_parse,
+};
+
+/*
+ * Module stuff
+ */
+static int __init pgp_key_init(void)
+{
+ return register_asymmetric_key_parser(&pgp_key_parser);
+}
+
+static void __exit pgp_key_exit(void)
+{
+ unregister_asymmetric_key_parser(&pgp_key_parser);
+}
+
+module_init(pgp_key_init);
+module_exit(pgp_key_exit);
--
2.34.1