[RFC PATCH 13/24] crypto/krb5: Implement the Kerberos5 rfc3961 get_mic and verify_mic

[David Howells <dhowells@redhat.com>]

Add functions that sign and verify a message according to rfc3961 sec 5.4,
using Kc to generate a checksum and insert it into the MIC field in the
skbuff in the sign phase then checksum the data and compare it to the MIC
in the verify phase.

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/internal.h           |  10 +++
 crypto/krb5/rfc3961_simplified.c | 130 +++++++++++++++++++++++++++++++
 2 files changed, 140 insertions(+)

diff --git a/crypto/krb5/internal.h b/crypto/krb5/internal.h
index 4533fb342953..eaaa9c13c8b3 100644
--- a/crypto/krb5/internal.h
+++ b/crypto/krb5/internal.h
@@ -169,3 +169,13 @@ int krb5_aead_decrypt(const struct krb5_enctype *krb5,
 		      struct crypto_aead *aead,
 		      struct scatterlist *sg, unsigned int nr_sg,
 		      size_t *_offset, size_t *_len);
+ssize_t rfc3961_get_mic(const struct krb5_enctype *krb5,
+			struct crypto_shash *shash,
+			const struct krb5_buffer *metadata,
+			struct scatterlist *sg, unsigned int nr_sg, size_t sg_len,
+			size_t data_offset, size_t data_len);
+int rfc3961_verify_mic(const struct krb5_enctype *krb5,
+		       struct crypto_shash *shash,
+		       const struct krb5_buffer *metadata,
+		       struct scatterlist *sg, unsigned int nr_sg,
+		       size_t *_offset, size_t *_len);
diff --git a/crypto/krb5/rfc3961_simplified.c b/crypto/krb5/rfc3961_simplified.c
index 55f295f3ac5f..59f0e7c823f7 100644
--- a/crypto/krb5/rfc3961_simplified.c
+++ b/crypto/krb5/rfc3961_simplified.c
@@ -647,6 +647,134 @@ int krb5_aead_decrypt(const struct krb5_enctype *krb5,
 	return ret;
 }
 
+/*
+ * Generate a checksum over some metadata and part of an skbuff and insert the
+ * MIC into the skbuff immediately prior to the data.
+ */
+ssize_t rfc3961_get_mic(const struct krb5_enctype *krb5,
+			struct crypto_shash *shash,
+			const struct krb5_buffer *metadata,
+			struct scatterlist *sg, unsigned int nr_sg, size_t sg_len,
+			size_t data_offset, size_t data_len)
+{
+	struct shash_desc *desc;
+	ssize_t ret, done;
+	size_t bsize;
+	void *buffer, *digest;
+
+	if (WARN_ON(data_offset != krb5->cksum_len))
+		return -EMSGSIZE;
+
+	bsize = krb5_shash_size(shash) +
+		krb5_digest_size(shash);
+	buffer = kzalloc(bsize, GFP_NOFS);
+	if (!buffer)
+		return -ENOMEM;
+
+	/* Calculate the MIC with key Kc and store it into the skb */
+	desc = buffer;
+	desc->tfm = shash;
+	ret = crypto_shash_init(desc);
+	if (ret < 0)
+		goto error;
+
+	if (metadata) {
+		ret = crypto_shash_update(desc, metadata->data, metadata->len);
+		if (ret < 0)
+			goto error;
+	}
+
+	ret = crypto_shash_update_sg(desc, sg, data_offset, data_len);
+	if (ret < 0)
+		goto error;
+
+	digest = buffer + krb5_shash_size(shash);
+	ret = crypto_shash_final(desc, digest);
+	if (ret < 0)
+		goto error;
+
+	ret = -EFAULT;
+	done = sg_pcopy_from_buffer(sg, nr_sg, digest, krb5->cksum_len,
+				    data_offset - krb5->cksum_len);
+	if (done != krb5->cksum_len)
+		goto error;
+
+	ret = krb5->cksum_len + data_len;
+
+error:
+	kfree_sensitive(buffer);
+	return ret;
+}
+
+/*
+ * Check the MIC on a region of an skbuff.  The offset and length are updated
+ * to reflect the actual content of the secure region.
+ */
+int rfc3961_verify_mic(const struct krb5_enctype *krb5,
+		       struct crypto_shash *shash,
+		       const struct krb5_buffer *metadata,
+		       struct scatterlist *sg, unsigned int nr_sg,
+		       size_t *_offset, size_t *_len)
+{
+	struct shash_desc *desc;
+	ssize_t done;
+	size_t bsize, data_offset, data_len, offset = *_offset, len = *_len;
+	void *buffer = NULL;
+	int ret;
+	u8 *cksum, *cksum2;
+
+	if (len < krb5->cksum_len)
+		return -EPROTO;
+	data_offset = offset + krb5->cksum_len;
+	data_len = len - krb5->cksum_len;
+
+	bsize = krb5_shash_size(shash) +
+		krb5_digest_size(shash) * 2;
+	buffer = kzalloc(bsize, GFP_NOFS);
+	if (!buffer)
+		return -ENOMEM;
+
+	cksum = buffer +
+		krb5_shash_size(shash);
+	cksum2 = buffer +
+		krb5_shash_size(shash) +
+		krb5_digest_size(shash);
+
+	/* Calculate the MIC */
+	desc = buffer;
+	desc->tfm = shash;
+	ret = crypto_shash_init(desc);
+	if (ret < 0)
+		goto error;
+
+	if (metadata) {
+		ret = crypto_shash_update(desc, metadata->data, metadata->len);
+		if (ret < 0)
+			goto error;
+	}
+
+	crypto_shash_update_sg(desc, sg, data_offset, data_len);
+	crypto_shash_final(desc, cksum);
+
+	ret = -EFAULT;
+	done = sg_pcopy_to_buffer(sg, nr_sg, cksum2, krb5->cksum_len, offset);
+	if (done != krb5->cksum_len)
+		goto error;
+
+	if (memcmp(cksum, cksum2, krb5->cksum_len) != 0) {
+		ret = -EBADMSG;
+		goto error;
+	}
+
+	*_offset += krb5->cksum_len;
+	*_len -= krb5->cksum_len;
+	ret = 0;
+
+error:
+	kfree_sensitive(buffer);
+	return ret;
+}
+
 const struct krb5_crypto_profile rfc3961_simplified_profile = {
 	.calc_PRF		= rfc3961_calc_PRF,
 	.calc_Kc		= rfc3961_calc_DK,
@@ -658,4 +786,6 @@ const struct krb5_crypto_profile rfc3961_simplified_profile = {
 	.load_checksum_key	= rfc3961_load_checksum_key,
 	.encrypt		= krb5_aead_encrypt,
 	.decrypt		= krb5_aead_decrypt,
+	.get_mic		= rfc3961_get_mic,
+	.verify_mic		= rfc3961_verify_mic,
 };