[PATCH v3 16/18] crypto: rsa-psspad: Implement signature verify callback

Varad Gautam
2021-04-20T11:47:11Z

The RSA output must be processed as per the EMSA-PSS-VERIFY operation
from RFC8017, which forms the core of the PSS signature verification.

Implement the verification callback, which operates on the RSA output
buffer.

Reference: https://tools.ietf.org/html/rfc8017#section-9.1.2
Signed-off-by: Varad Gautam <varad.gautam@suse.com>
---
crypto/rsa-psspad.c | 114 +++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 113 insertions(+), 1 deletion(-)

diff --git a/crypto/rsa-psspad.c b/crypto/rsa-psspad.c
index 4e8525d89172d..c6f8fb43cb01e 100644
--- a/crypto/rsa-psspad.c
+++ b/crypto/rsa-psspad.c
@@ -8,6 +8,7 @@

#include <crypto/hash.h>
#include <crypto/internal/akcipher.h>
+#include <crypto/internal/rsa.h>
#include <crypto/internal/rsa-common.h>
#include <crypto/public_key.h>

@@ -126,7 +127,118 @@ static int pkcs1_mgf1(u8 *seed, unsigned int seed_len,

static int psspad_verify_complete(struct akcipher_request *req, int err)
{
- return -EOPNOTSUPP;
+ struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
+ struct rsapad_tfm_ctx *ctx = akcipher_tfm_ctx(tfm);
+ struct rsapad_akciper_req_ctx *req_ctx = akcipher_request_ctx(req);
+ struct akcipher_instance *inst = akcipher_alg_instance(tfm);
+ struct rsapad_inst_ctx *ictx = akcipher_instance_ctx(inst);
+ const struct rsa_asn1_template *digest_info = ictx->digest_info;
+ struct crypto_shash *hash_tfm = NULL;
+ struct shash_desc *desc = NULL;
+ struct rsa_mpi_key *pkey = akcipher_tfm_ctx(ctx->child);
+
+ u8 *em, *h, *salt, *maskeddb;
+ unsigned int em_len, em_bits, h_len, s_len, maskeddb_len;
+ u8 *m_hash, *db_mask, *db, *h_;
+ static u8 zeroes[8] = { 0 };
+ unsigned int pos;
+
+ if (err)
+ goto out;
+
+ err = -EINVAL;
+ if (!digest_info)
+ goto out;
+
+ em = req_ctx->out_buf;
+ em_len = ctx->key_size;
+ em_bits = mpi_get_nbits(pkey->n) - 1;
+ if ((em_bits & 0x7) == 0) {
+ em_len--;
+ em++;
+ }
+
+ h_len = req->dst_len;
+ s_len = ictx->salt_len;
+
+ if (em_len < h_len + s_len + 2)
+ goto out;
+
+ if (em[em_len - 1] != 0xbc)
+ goto out;
+
+ maskeddb = em;
+ maskeddb_len = em_len - h_len - 1;
+ h = em + maskeddb_len;
+
+ if (em[0] & ~((u8) 0xff >> (8 * em_len - em_bits)))
+ goto out;
+
+ db_mask = kzalloc(maskeddb_len, GFP_KERNEL);
+ if (!db_mask) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ err = psspad_setup_shash(&hash_tfm, &desc, ictx->mgf_hash_algo);
+ if (err < 0)
+ goto out_db_mask;
+
+ err = pkcs1_mgf1(h, h_len, desc, db_mask, maskeddb_len);
+ if (err < 0)
+ goto out_shash;
+
+ for (pos = 0; pos < maskeddb_len; pos++)
+ maskeddb[pos] ^= db_mask[pos];
+ db = maskeddb;
+
+ db[0] &= ((u8) 0xff >> (8 * em_len - em_bits));
+
+ err = -EINVAL;
+ for (pos = 0; pos < em_len - h_len - s_len - 2; pos++) {
+ if (db[pos] != 0)
+ goto out_shash;
+ }
+ if (db[pos] != 0x01)
+ goto out_shash;
+
+ salt = db + (maskeddb_len - s_len);
+
+ m_hash = req_ctx->out_buf + ctx->key_size;
+ sg_pcopy_to_buffer(req->src,
+ sg_nents_for_len(req->src, req->src_len + req->dst_len),
+ m_hash,
+ req->dst_len, ctx->key_size);
+
+ if (strcmp(ictx->mgf_hash_algo, digest_info->name) != 0) {
+ psspad_free_shash(hash_tfm, desc);
+ err = psspad_setup_shash(&hash_tfm, &desc, digest_info->name);
+ if (err < 0)
+ goto out_db_mask;
+ }
+
+ err = crypto_shash_init(desc);
+ if (!err)
+ err = crypto_shash_update(desc, zeroes, 8);
+ if (!err)
+ err = crypto_shash_update(desc, m_hash, h_len);
+ if (!err)
+ err = crypto_shash_finup(desc, salt, s_len, m_hash);
+ if (err < 0)
+ goto out_shash;
+
+ h_ = m_hash;
+
+ if (memcmp(h_, h, h_len) != 0)
+ err = -EKEYREJECTED;
+
+out_shash:
+ psspad_free_shash(hash_tfm, desc);
+out_db_mask:
+ kfree(db_mask);
+out:
+ kfree_sensitive(req_ctx->out_buf);
+ return err;
}

static void psspad_verify_complete_cb(struct crypto_async_request *child_async_req,
--
2.30.2