[RFC PATCH 16/24] crypto/krb5: Implement the AES encrypt/decrypt from rfc8009

David Howells
2025-01-17T18:37:30Z

Implement encryption and decryption functions for AES + HMAC-SHA2 as
described in rfc8009 sec 5.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: "David S. Miller" <davem@davemloft.net>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-crypto@vger.kernel.org
cc: netdev@vger.kernel.org
---
crypto/krb5/rfc8009_aes2.c | 139 ++++++++++++++++++++++++++++++++++++-
1 file changed, 137 insertions(+), 2 deletions(-)

diff --git a/crypto/krb5/rfc8009_aes2.c b/crypto/krb5/rfc8009_aes2.c
index d7225187ce8b..bcf84284abff 100644
--- a/crypto/krb5/rfc8009_aes2.c
+++ b/crypto/krb5/rfc8009_aes2.c
@@ -234,6 +234,141 @@ int authenc_load_encrypt_keys(const struct krb5_enctype *krb5,
return 0;
}

+/*
+ * Apply encryption and checksumming functions to a message. Unlike for
+ * RFC3961, for RFC8009, we have to chuck the starting IV into the hash first.
+ */
+static ssize_t rfc8009_encrypt(const struct krb5_enctype *krb5,
+ struct crypto_aead *aead,
+ struct scatterlist *sg, unsigned int nr_sg, size_t sg_len,
+ size_t data_offset, size_t data_len,
+ bool preconfounded)
+{
+ struct aead_request *req;
+ struct scatterlist bsg[2];
+ ssize_t ret, done;
+ size_t bsize, base_len, secure_offset, secure_len, pad_len, cksum_offset;
+ void *buffer;
+ u8 *iv, *ad;
+
+ if (WARN_ON(data_offset != krb5->conf_len))
+ return -EINVAL; /* Data is in wrong place */
+
+ secure_offset = 0;
+ base_len = krb5->conf_len + data_len;
+ pad_len = 0;
+ secure_len = base_len + pad_len;
+ cksum_offset = secure_len;
+ if (WARN_ON(cksum_offset + krb5->cksum_len > sg_len))
+ return -EFAULT;
+
+ bsize = krb5_aead_size(aead) +
+ krb5_aead_ivsize(aead) * 2;
+ buffer = kzalloc(bsize, GFP_NOFS);
+ if (!buffer)
+ return -ENOMEM;
+
+ req = buffer;
+ iv = buffer + krb5_aead_size(aead);
+ ad = buffer + krb5_aead_size(aead) + krb5_aead_ivsize(aead);
+
+ /* Insert the confounder into the buffer */
+ ret = -EFAULT;
+ if (!preconfounded) {
+ get_random_bytes(buffer, krb5->conf_len);
+ done = sg_pcopy_from_buffer(sg, nr_sg, buffer, krb5->conf_len,
+ secure_offset);
+ if (done != krb5->conf_len)
+ goto error;
+ }
+
+ /* We may need to pad out to the crypto blocksize. */
+ if (pad_len) {
+ done = sg_zero_buffer(sg, nr_sg, pad_len, data_offset + data_len);
+ if (done != pad_len)
+ goto error;
+ }
+
+ /* We need to include the starting IV in the hash. */
+ sg_init_table(bsg, 2);
+ sg_set_buf(&bsg[0], ad, krb5_aead_ivsize(aead));
+ sg_chain(bsg, 2, sg);
+
+ /* Hash and encrypt the message. */
+ aead_request_set_tfm(req, aead);
+ aead_request_set_callback(req, 0, NULL, NULL);
+ aead_request_set_ad(req, krb5_aead_ivsize(aead));
+ aead_request_set_crypt(req, bsg, bsg, secure_len, iv);
+ ret = crypto_aead_encrypt(req);
+ if (ret < 0)
+ goto error;
+
+ ret = secure_len + krb5->cksum_len;
+
+error:
+ kfree_sensitive(buffer);
+ return ret;
+}
+
+/*
+ * Apply decryption and checksumming functions to a message. Unlike for
+ * RFC3961, for RFC8009, we have to chuck the starting IV into the hash first.
+ *
+ * The offset and length are updated to reflect the actual content of the
+ * encrypted region.
+ */
+static int rfc8009_decrypt(const struct krb5_enctype *krb5,
+ struct crypto_aead *aead,
+ struct scatterlist *sg, unsigned int nr_sg,
+ size_t *_offset, size_t *_len)
+{
+ struct aead_request *req;
+ struct scatterlist bsg[2];
+ size_t bsize;
+ void *buffer;
+ int ret;
+ u8 *iv, *ad;
+
+ if (WARN_ON(*_offset != 0))
+ return -EINVAL; /* Can't set offset on aead */
+
+ if (*_len < krb5->conf_len + krb5->cksum_len)
+ return -EPROTO;
+
+ bsize = krb5_aead_size(aead) +
+ krb5_aead_ivsize(aead) * 2;
+ buffer = kzalloc(bsize, GFP_NOFS);
+ if (!buffer)
+ return -ENOMEM;
+
+ req = buffer;
+ iv = buffer + krb5_aead_size(aead);
+ ad = buffer + krb5_aead_size(aead) + krb5_aead_ivsize(aead);
+
+ /* We need to include the starting IV in the hash. */
+ sg_init_table(bsg, 2);
+ sg_set_buf(&bsg[0], ad, krb5_aead_ivsize(aead));
+ sg_chain(bsg, 2, sg);
+
+ /* Decrypt the message and verify its checksum. */
+ aead_request_set_tfm(req, aead);
+ aead_request_set_callback(req, 0, NULL, NULL);
+ aead_request_set_ad(req, krb5_aead_ivsize(aead));
+ aead_request_set_crypt(req, bsg, bsg, *_len, iv);
+ ret = crypto_aead_decrypt(req);
+ if (ret < 0)
+ goto error;
+
+ /* Adjust the boundaries of the data. */
+ *_offset += krb5->conf_len;
+ *_len -= krb5->conf_len + krb5->cksum_len;
+ ret = 0;
+
+error:
+ kfree_sensitive(buffer);
+ return ret;
+}
+
static const struct krb5_crypto_profile rfc8009_crypto_profile = {
.calc_PRF = rfc8009_calc_PRF,
.calc_Kc = rfc8009_calc_Ki,
@@ -243,8 +378,8 @@ static const struct krb5_crypto_profile rfc8009_crypto_profile = {
.load_encrypt_keys = authenc_load_encrypt_keys,
.derive_checksum_key = rfc3961_derive_checksum_key,
.load_checksum_key = rfc3961_load_checksum_key,
- .encrypt = NULL, //rfc8009_encrypt,
- .decrypt = NULL, //rfc8009_decrypt,
+ .encrypt = rfc8009_encrypt,
+ .decrypt = rfc8009_decrypt,
.get_mic = rfc3961_get_mic,
.verify_mic = rfc3961_verify_mic,
};