From 7d52d0bd861c3aeaea5214131ef64543d63ea309 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sun, 29 Sep 2019 13:29:09 +0100
Subject: [PATCH] hash: Put hash state on the caller's stack

This makes the code simpler too!

We rename len to slen, to distinguish hlen and slen (to help avoid
bugs where the wrong amount is allocated).

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 md5.c    | 15 ++++++---------
 rsa.c    |  9 +++++----
 secnet.h |  7 ++++---
 sha1.c   | 15 ++++++---------
 4 files changed, 21 insertions(+), 25 deletions(-)

diff --git a/md5.c b/md5.c
index 738d81a..caaa5a6 100644
--- a/md5.c
+++ b/md5.c
@@ -238,14 +238,11 @@ MD5Transform(uint32_t buf[4], uint32_t const in[16])
 
 #endif
 
-static void *md5_init(void)
+static void md5_init(void *sst)
 {
-    struct MD5Context *ctx;
+    struct MD5Context *ctx=sst;
 
-    NEW(ctx);
     MD5Init(ctx);
-
-    return ctx;
 }
 
 static void md5_update(void *sst, const void *buf, int32_t len)
@@ -260,7 +257,6 @@ static void md5_final(void *sst, uint8_t *digest)
     struct MD5Context *ctx=sst;
 
     MD5Final(digest,ctx);
-    free(ctx);
 }
 
 struct md5 {
@@ -271,7 +267,6 @@ struct md5 {
 void md5_module(dict_t *dict)
 {
     struct md5 *st;
-    void *ctx;
     cstring_t testinput="12345\n";
     uint8_t expected[16]=
 	{0xd5,0x77,0x27,0x3f,0xf8,0x85,0xc3,0xf8,
@@ -284,14 +279,16 @@ void md5_module(dict_t *dict)
     st->cl.type=CL_HASH;
     st->cl.apply=NULL;
     st->cl.interface=&st->ops;
-    st->ops.len=16;
+    st->ops.hlen=16;
+    st->ops.slen=sizeof(struct MD5Context);
     st->ops.init=md5_init;
     st->ops.update=md5_update;
     st->ops.final=md5_final;
 
     dict_add(dict,"md5",new_closure(&st->cl));
 
-    ctx=md5_init();
+    uint8_t ctx[st->ops.slen];
+    md5_init(ctx);
     md5_update(ctx,testinput,strlen(testinput));
     md5_final(ctx,digest);
     for (i=0; i<16; i++) {
diff --git a/rsa.c b/rsa.c
index 81754a7..c87fcb7 100644
--- a/rsa.c
+++ b/rsa.c
@@ -77,7 +77,7 @@ static const char *hexchars="0123456789abcdef";
 static void rsa_sethash(struct rsacommon *c, struct hash_if *hash)
 {
     free(c->hashbuf);
-    c->hashbuf=safe_malloc(hash->len, "generate_msg");
+    c->hashbuf=safe_malloc(hash->hlen, "generate_msg");
     c->hashi=hash;
 }
 static void rsa_pub_sethash(void *sst, struct hash_if *hash)
@@ -92,7 +92,8 @@ static void rsa_priv_sethash(void *sst, struct hash_if *hash)
 }
 static void rsa_hash(struct rsacommon *c, const uint8_t *buf, int32_t len)
 {
-    void *hst=c->hashi->init();
+    uint8_t hst[c->hashi->slen];
+    c->hashi->init(hst);
     c->hashi->update(hst,buf,len);
     c->hashi->final(hst,c->hashbuf);
 }
@@ -158,7 +159,7 @@ static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
 
     rsa_hash(&st->common,data,datalen);
     /* Construct the message representative. */
-    emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->len);
+    emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->hlen);
 
     /*
      * Produce an RSA signature (a^d mod n) using the Chinese
@@ -245,7 +246,7 @@ static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
     mpz_init(&c);
 
     rsa_hash(&st->common,data,datalen);
-    emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->len);
+    emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->hlen);
 
     /* Terminate signature with a '0' - already checked that this will fit */
     int save = sig->sigstart[sig->siglen];
diff --git a/secnet.h b/secnet.h
index d2575f1..c6e8f49 100644
--- a/secnet.h
+++ b/secnet.h
@@ -643,11 +643,12 @@ struct dh_if {
 
 /* HASH interface */
 
-typedef void *hash_init_fn(void);
+typedef void hash_init_fn(void *st /* slen bytes alloc'd by caller */);
 typedef void hash_update_fn(void *st, const void *buf, int32_t len);
-typedef void hash_final_fn(void *st, uint8_t *digest);
+typedef void hash_final_fn(void *st, uint8_t *digest /* hlen bytes */);
 struct hash_if {
-    int32_t len; /* Hash output length in bytes */
+    int32_t slen; /* State length in bytes */
+    int32_t hlen; /* Hash output length in bytes */
     hash_init_fn *init;
     hash_update_fn *update;
     hash_final_fn *final;
diff --git a/sha1.c b/sha1.c
index 4cc63b5..b11c25a 100644
--- a/sha1.c
+++ b/sha1.c
@@ -287,14 +287,11 @@ unsigned char finalcount[8];
 /*************************************************************/
 
 /* Everything below here is the interface to secnet */
-static void *sha1_init(void)
+static void sha1_init(void *sst)
 {
-    SHA1_CTX *ctx;
+    SHA1_CTX *ctx=sst;
 
-    NEW(ctx);
     SHA1Init(ctx);
-
-    return ctx;
 }
 
 static void sha1_update(void *sst, const void *buf, int32_t len)
@@ -309,7 +306,6 @@ static void sha1_final(void *sst, uint8_t *digest)
     SHA1_CTX *ctx=sst;
 
     SHA1Final(digest,ctx);
-    free(ctx);
 }
 
 struct sha1 {
@@ -320,7 +316,6 @@ struct sha1 {
 void sha1_module(dict_t *dict)
 {
     struct sha1 *st;
-    void *ctx;
     cstring_t testinput="abcdbcdecdefdefgefghfghigh"
 	"ijhijkijkljklmklmnlmnomnopnopq";
     uint8_t expected[20]=
@@ -337,14 +332,16 @@ void sha1_module(dict_t *dict)
     st->cl.type=CL_HASH;
     st->cl.apply=NULL;
     st->cl.interface=&st->ops;
-    st->ops.len=20;
+    st->ops.hlen=20;
+    st->ops.slen=sizeof(SHA1_CTX);
     st->ops.init=sha1_init;
     st->ops.update=sha1_update;
     st->ops.final=sha1_final;
 
     dict_add(dict,"sha1",new_closure(&st->cl));
 
-    ctx=sha1_init();
+    uint8_t ctx[st->ops.slen];
+    sha1_init(ctx);
     sha1_update(ctx,testinput,strlen(testinput));
     sha1_final(ctx,digest);
     for (i=0; i<20; i++) {
-- 
2.30.2