From e15f70f41d691fc1e6cc82fb398429cdb3444342 Mon Sep 17 00:00:00 2001
From: Andre Noll <maan@tuebingen.mpg.de>
Date: Sun, 7 May 2023 18:01:43 +0200
Subject: [PATCH] apc_priv_decrypt: Let the callee allocate the buffer.

This complements the previous commit which made the analogous
change for public encryption. Passing char ** instead of char * to
apc_priv_decrypt() allows us to get rid of the magic 1024 constant
in client_common.c.
---
 client_common.c |  6 ++++--
 crypt.h         |  4 ++--
 gcrypt.c        | 12 ++++++++----
 openssl.c       | 11 ++++++++---
 4 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/client_common.c b/client_common.c
index 32a94492..396fd88c 100644
--- a/client_common.c
+++ b/client_common.c
@@ -324,7 +324,7 @@ static int client_post_monitor(struct sched *s, void *context)
 		 */
 		{
 		/* decrypted challenge/session key buffer */
-		unsigned char crypt_buf[1024];
+		unsigned char *crypt_buf;
 		struct sb_buffer sbb;
 
 		ret = recv_sb(ct, &sbb);
@@ -337,12 +337,13 @@ static int client_post_monitor(struct sched *s, void *context)
 		}
 		n = sbb.iov.iov_len;
 		PARA_INFO_LOG("<-- [challenge] (%zu bytes)\n", n);
-		ret = apc_priv_decrypt(ct->key_file, crypt_buf,
+		ret = apc_priv_decrypt(ct->key_file, &crypt_buf,
 			sbb.iov.iov_base, n);
 		free(sbb.iov.iov_base);
 		if (ret < 0)
 			goto out;
 		if (ret != APC_CHALLENGE_SIZE + 2 * SESSION_KEY_LEN) {
+			free(crypt_buf);
 			ret = -E_DECRYPT;
 			goto out;
 		}
@@ -360,6 +361,7 @@ static int client_post_monitor(struct sched *s, void *context)
 			 SESSION_KEY_LEN);
 		ct->scc.recv = sc_new(crypt_buf + APC_CHALLENGE_SIZE
 			+ SESSION_KEY_LEN, SESSION_KEY_LEN);
+		free(crypt_buf);
 		PARA_INFO_LOG("--> %s\n", buf);
 		ct->status = CL_RECEIVED_CHALLENGE;
 		return 0;
diff --git a/crypt.h b/crypt.h
index 65070995..2e094ced 100644
--- a/crypt.h
+++ b/crypt.h
@@ -31,7 +31,7 @@ int apc_pub_encrypt(struct asymmetric_key *pub, unsigned char *inbuf,
  * Decrypt a buffer using a private key.
  *
  * \param key_file Full path of the key.
- * \param outbuf The output buffer.
+ * \param outbuf The output buffer is allocated by the callee.
  * \param inbuf The encrypted input buffer.
  * \param inlen The length of \a inbuf.
  *
@@ -39,7 +39,7 @@ int apc_pub_encrypt(struct asymmetric_key *pub, unsigned char *inbuf,
  *
  * \return The size of the recovered plaintext on success, negative on errors.
  */
-int apc_priv_decrypt(const char *key_file, unsigned char *outbuf,
+int apc_priv_decrypt(const char *key_file, unsigned char **outbuf,
 		unsigned char *inbuf, int inlen);
 
 /**
diff --git a/gcrypt.c b/gcrypt.c
index 68f80f27..e5f64688 100644
--- a/gcrypt.c
+++ b/gcrypt.c
@@ -478,17 +478,20 @@ void apc_free_pubkey(struct asymmetric_key *key)
 	free(key);
 }
 
-static int decode_rsa(gcry_sexp_t sexp, unsigned char *outbuf, size_t *nbytes)
+static int decode_rsa(gcry_sexp_t sexp, unsigned char **outbuf, size_t *nbytes)
 {
 	const char *p = gcry_sexp_nth_data(sexp, 1, nbytes);
 
-	if (!p)
+	if (!p) {
+		*outbuf = NULL;
 		return -E_RSA_DECODE;
-	memcpy(outbuf, p, *nbytes);
+	}
+	*outbuf = alloc(*nbytes);
+	memcpy(*outbuf, p, *nbytes);
 	return 1;
 }
 
-int apc_priv_decrypt(const char *key_file, unsigned char *outbuf,
+int apc_priv_decrypt(const char *key_file, unsigned char **outbuf,
 		unsigned char *inbuf, int inlen)
 {
 	gcry_error_t gret;
@@ -498,6 +501,7 @@ int apc_priv_decrypt(const char *key_file, unsigned char *outbuf,
 	gcry_sexp_t in, out, priv_key;
 	size_t nbytes;
 
+	*outbuf = NULL;
 	ret = check_private_key_file(key_file);
 	if (ret < 0)
 		return ret;
diff --git a/openssl.c b/openssl.c
index acf1120d..5f981437 100644
--- a/openssl.c
+++ b/openssl.c
@@ -274,12 +274,13 @@ void apc_free_pubkey(struct asymmetric_key *pub)
 	free(pub);
 }
 
-int apc_priv_decrypt(const char *key_file, unsigned char *outbuf,
+int apc_priv_decrypt(const char *key_file, unsigned char **outbuf,
 		unsigned char *inbuf, int inlen)
 {
 	struct asymmetric_key *priv;
 	int ret;
 
+	*outbuf = NULL;
 	ret = check_private_key_file(key_file);
 	if (ret < 0)
 		return ret;
@@ -298,11 +299,15 @@ int apc_priv_decrypt(const char *key_file, unsigned char *outbuf,
 	ret = -E_BLINDING;
 	if (RSA_blinding_on(priv->rsa, NULL) == 0)
 		goto out;
-	ret = RSA_private_decrypt(inlen, inbuf, outbuf, priv->rsa,
+	*outbuf = alloc(RSA_size(priv->rsa));
+	ret = RSA_private_decrypt(inlen, inbuf, *outbuf, priv->rsa,
 		RSA_PKCS1_OAEP_PADDING);
 	RSA_blinding_off(priv->rsa);
-	if (ret <= 0)
+	if (ret <= 0) {
+		free(*outbuf);
+		*outbuf = NULL;
 		ret = -E_DECRYPT;
+	}
 out:
 	RSA_free(priv->rsa);
 	free(priv);
-- 
2.39.5