[PATCH v3 05/14] PGPLIB: Signature parser

Roberto Sassu
2024-09-11T12:30:12Z

From: David Howells <dhowells@redhat.com>

Provide some PGP signature parsing helpers:

(1) A function to parse V4 signature subpackets and pass the desired ones
to a processor function:

int pgp_parse_sig_subpkts(const u8 *data, size_t datalen,
struct pgp_parse_sig_context *ctx);

(2) A function to parse out basic signature parameters from any PGP
signature such that the algorithms and public key can be selected:

int pgp_parse_sig_params(const u8 **_data, size_t *_datalen,
struct pgp_sig_parameters *p);

Signed-off-by: David Howells <dhowells@redhat.com>
Co-developed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
crypto/asymmetric_keys/pgp_library.c | 284 +++++++++++++++++++++++++++
crypto/asymmetric_keys/pgplib.h | 25 +++
2 files changed, 309 insertions(+)

diff --git a/crypto/asymmetric_keys/pgp_library.c b/crypto/asymmetric_keys/pgp_library.c
index 1b87f8af411b..a9708ccbcb81 100644
--- a/crypto/asymmetric_keys/pgp_library.c
+++ b/crypto/asymmetric_keys/pgp_library.c
@@ -260,3 +260,287 @@ int pgp_parse_public_key(const u8 **_data, size_t *_datalen,
return 0;
}
EXPORT_SYMBOL_GPL(pgp_parse_public_key);
+
+/**
+ * pgp_parse_sig_subpkt_header - Parse a PGP V4 signature subpacket header
+ * @_data: Start of the subpacket (updated to subpacket data)
+ * @_datalen: Amount of data remaining in buffer (decreased)
+ * @_type: Where the subpacket type will be returned
+ *
+ * Parse a PGP V4 signature subpacket header [RFC 9580: 5.2.3.7].
+ *
+ * Return: packet data size on success; non-zero on error. If successful,
+ * *_data and *_datalen will have been updated and *_headerlen will be set to
+ * hold the length of the packet header.
+ */
+static ssize_t pgp_parse_sig_subpkt_header(const u8 **_data, size_t *_datalen,
+ enum pgp_sig_subpkt_type *_type)
+{
+ enum pgp_sig_subpkt_type type;
+ const u8 *data = *_data;
+ size_t size, datalen = *_datalen;
+
+ pr_devel("-->%s(,%zu,,)\n", __func__, datalen);
+
+ if (datalen < 2)
+ goto short_subpacket;
+
+ pr_devel("subpkt hdr %02x, %02x\n", data[0], data[1]);
+
+ switch (data[0]) {
+ case 0x00 ... 0xbf:
+ /* One-byte length */
+ size = data[0];
+ data++;
+ datalen--;
+ break;
+ case 0xc0 ... 0xfe:
+ /* Two-byte length */
+ if (datalen < 3)
+ goto short_subpacket;
+ size = (data[0] - 192) * 256;
+ size += data[1] + 192;
+ data += 2;
+ datalen -= 2;
+ break;
+ case 0xff:
+ if (datalen < 6)
+ goto short_subpacket;
+ size = data[1] << 24;
+ size |= data[2] << 16;
+ size |= data[3] << 8;
+ size |= data[4];
+ data += 5;
+ datalen -= 5;
+ break;
+ }
+
+ /* The type octet is included in the size */
+ pr_devel("datalen=%zu size=%zu\n", datalen, size);
+ if (datalen < size)
+ goto short_subpacket;
+ if (size == 0)
+ goto very_short_subpacket;
+ if (size > INT_MAX)
+ goto too_big;
+
+ type = *data++ & ~PGP_SIG_SUBPKT_TYPE_CRITICAL_MASK;
+ datalen--;
+ size--;
+
+ *_data = data;
+ *_datalen = datalen;
+ *_type = type;
+ pr_devel("Found subpkt type=%u size=%zd\n", type, size);
+ return size;
+
+very_short_subpacket:
+ pr_debug("Signature subpacket size can't be zero\n");
+ return -EBADMSG;
+short_subpacket:
+ pr_debug("Attempt to parse short signature subpacket\n");
+ return -EBADMSG;
+too_big:
+ pr_debug("Signature subpacket size >2G\n");
+ return -EMSGSIZE;
+}
+
+/**
+ * pgp_parse_sig_subpkts - Parse a set of PGP V4 signatute subpackets
+ * @data: Data to be parsed (updated)
+ * @datalen: Amount of data (updated)
+ * @ctx: Parsing context
+ *
+ * Parse a set of PGP signature subpackets [RFC 9580: 5.2.3].
+ *
+ * Return: 0 on successful parsing, an error value otherwise.
+ */
+static int pgp_parse_sig_subpkts(const u8 *data, size_t datalen,
+ struct pgp_parse_sig_context *ctx)
+{
+ enum pgp_sig_subpkt_type type;
+ ssize_t pktlen;
+ int ret;
+
+ pr_devel("-->%s(,%zu,,)\n", __func__, datalen);
+
+ while (datalen > 2) {
+ pktlen = pgp_parse_sig_subpkt_header(&data, &datalen, &type);
+ if (pktlen < 0)
+ return pktlen;
+ if (test_bit(type, ctx->types_of_interest)) {
+ ret = ctx->process_packet(ctx, type, data, pktlen);
+ if (ret < 0)
+ return ret;
+ }
+ data += pktlen;
+ datalen -= pktlen;
+ }
+
+ if (datalen != 0) {
+ pr_debug("Excess octets in signature subpacket stream\n");
+ return -EBADMSG;
+ }
+
+ return 0;
+}
+
+struct pgp_parse_sig_params_ctx {
+ struct pgp_parse_sig_context base;
+ struct pgp_sig_parameters *params;
+ bool got_the_issuer;
+};
+
+/*
+ * Process a V4 signature subpacket.
+ */
+static int pgp_process_sig_params_subpkt(struct pgp_parse_sig_context *context,
+ enum pgp_sig_subpkt_type type,
+ const u8 *data,
+ size_t datalen)
+{
+ struct pgp_parse_sig_params_ctx *ctx =
+ container_of(context, struct pgp_parse_sig_params_ctx, base);
+
+ if (ctx->got_the_issuer) {
+ pr_debug("V4 signature packet has multiple issuers\n");
+ return -EBADMSG;
+ }
+
+ if (datalen != 8) {
+ pr_debug("V4 signature issuer subpkt not 8 long (%zu)\n",
+ datalen);
+ return -EBADMSG;
+ }
+
+ memcpy(&ctx->params->issuer, data, 8);
+ ctx->got_the_issuer = true;
+ return 0;
+}
+
+/**
+ * pgp_parse_sig_params - Parse basic parameters from a PGP signature packet
+ * @_data: Content of packet (updated)
+ * @_datalen: Length of packet remaining (updated)
+ * @p: The basic parameters
+ *
+ * Parse the basic parameters from a PGP signature packet [RFC 9580: 5.2] that
+ * are needed to start off a signature verification operation. The only ones
+ * actually necessary are the signature type (which affects how the data is
+ * transformed) and the hash algorithm.
+ *
+ * We also extract the public key algorithm and the issuer's key ID as we'll
+ * need those to determine if we actually have the public key available. If
+ * not, then we can't verify the signature anyway.
+ *
+ * Return: 0 if successful or a negative error code. *_data and *_datalen are
+ * updated to point to the 16-bit subset of the hash value and the set of MPIs.
+ */
+int pgp_parse_sig_params(const u8 **_data, size_t *_datalen,
+ struct pgp_sig_parameters *p)
+{
+ const u8 *data = *_data;
+ size_t datalen = *_datalen;
+ int ret;
+
+ pr_devel("-->%s(,%zu,,)\n", __func__, datalen);
+
+ if (datalen < 1)
+ return -EBADMSG;
+ p->version = *data;
+
+ if (p->version == PGP_SIG_VERSION_3) {
+ const struct pgp_signature_v3_packet *v3 = (const void *)data;
+
+ if (datalen < sizeof(*v3)) {
+ pr_debug("Short V3 signature packet\n");
+ return -EBADMSG;
+ }
+ datalen -= sizeof(*v3);
+ data += sizeof(*v3);
+
+ /* V3 has everything we need in the header */
+ p->signature_type = v3->hashed.signature_type;
+ memcpy(&p->issuer, &v3->issuer, 8);
+ p->pubkey_algo = v3->pubkey_algo;
+ p->hash_algo = v3->hash_algo;
+
+ } else if (p->version == PGP_SIG_VERSION_4) {
+ const struct pgp_signature_v4_packet *v4 = (const void *)data;
+ struct pgp_parse_sig_params_ctx ctx = {
+ .base.process_packet = pgp_process_sig_params_subpkt,
+ .params = p,
+ .got_the_issuer = false,
+ };
+ size_t subdatalen;
+
+ if (datalen < sizeof(*v4) + 2 + 2 + 2) {
+ pr_debug("Short V4 signature packet\n");
+ return -EBADMSG;
+ }
+ datalen -= sizeof(*v4);
+ data += sizeof(*v4);
+
+ /* V4 has most things in the header... */
+ p->signature_type = v4->signature_type;
+ p->pubkey_algo = v4->pubkey_algo;
+ p->hash_algo = v4->hash_algo;
+
+ /*
+ * ... but we have to get the key ID from the subpackets, of
+ * which there are two sets.
+ */
+ __set_bit(PGP_SIG_ISSUER, ctx.base.types_of_interest);
+
+ subdatalen = *data++ << 8;
+ subdatalen |= *data++;
+ datalen -= 2;
+ if (subdatalen) {
+ /* Hashed subpackets */
+ pr_devel("hashed data: %zu (after %zu)\n",
+ subdatalen, sizeof(*v4));
+ if (subdatalen > datalen + 2 + 2) {
+ pr_debug("Short V4 signature packet [hdata]\n");
+ return -EBADMSG;
+ }
+ ret = pgp_parse_sig_subpkts(data, subdatalen,
+ &ctx.base);
+ if (ret < 0)
+ return ret;
+ data += subdatalen;
+ datalen -= subdatalen;
+ }
+
+ subdatalen = *data++ << 8;
+ subdatalen |= *data++;
+ datalen -= 2;
+ if (subdatalen) {
+ /* Unhashed subpackets */
+ pr_devel("unhashed data: %zu\n", subdatalen);
+ if (subdatalen > datalen + 2) {
+ pr_debug("Short V4 signature packet [udata]\n");
+ return -EBADMSG;
+ }
+ ret = pgp_parse_sig_subpkts(data, subdatalen,
+ &ctx.base);
+ if (ret < 0)
+ return ret;
+ data += subdatalen;
+ datalen -= subdatalen;
+ }
+
+ if (!ctx.got_the_issuer) {
+ pr_debug("V4 signature packet lacks issuer\n");
+ return -EBADMSG;
+ }
+ } else {
+ pr_debug("Signature packet with unhandled version %d\n",
+ p->version);
+ return -EBADMSG;
+ }
+
+ *_data = data;
+ *_datalen = datalen;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(pgp_parse_sig_params);
diff --git a/crypto/asymmetric_keys/pgplib.h b/crypto/asymmetric_keys/pgplib.h
index 3ec4b408a11e..25191cea33a4 100644
--- a/crypto/asymmetric_keys/pgplib.h
+++ b/crypto/asymmetric_keys/pgplib.h
@@ -31,3 +31,28 @@ struct pgp_parse_pubkey {

extern int pgp_parse_public_key(const u8 **_data, size_t *_datalen,
struct pgp_parse_pubkey *pk);
+
+struct pgp_parse_sig_context {
+ unsigned long types_of_interest[128 / BITS_PER_LONG];
+ int (*process_packet)(struct pgp_parse_sig_context *context,
+ enum pgp_sig_subpkt_type type,
+ const u8 *data,
+ size_t datalen);
+};
+
+extern int pgp_parse_sig_packets(const u8 *data, size_t datalen,
+ struct pgp_parse_sig_context *ctx);
+
+struct pgp_sig_parameters {
+ enum pgp_signature_version version : 8;
+ enum pgp_signature_type signature_type : 8;
+ enum pgp_pubkey_algo pubkey_algo : 8;
+ enum pgp_hash_algo hash_algo : 8;
+ union {
+ struct pgp_key_ID issuer;
+ __be32 issuer32[2];
+ };
+};
+
+extern int pgp_parse_sig_params(const u8 **_data, size_t *_datalen,
+ struct pgp_sig_parameters *p);
--
2.34.1