From 42379dfdd0d10c9ce9ba3f7c2c7e26083e240e68 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sat, 24 Aug 2019 10:17:57 -0700
Subject: sha256/md5: state-based hash: handle size_t overflow.

* chksum.c (sha256_szmax_upd, md5_szmax_upd): New static
functions, consisting of logic from sha256_buf and
md5_buf, respectively.
(sha256_buf, md5_buf): Use sha256_szmax_up and md5_szmax_upd,
respectively, to handle the unlikely possiblity of the ucnum
buffer length being larger than the range of size_t.
(sha256_hash, md5_hash): Also use the new static functions
instead of callig SHA256_update or MD5_update directly
to deal with the same issue.
---
 chksum.c | 40 ++++++++++++++++++++--------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/chksum.c b/chksum.c
index 09e9f3b5..8934583b 100644
--- a/chksum.c
+++ b/chksum.c
@@ -119,23 +119,23 @@ val sha256_stream(val stream, val nbytes, val buf_in)
   return buf;
 }
 
-static void sha256_buf(val buf, unsigned char *hash)
+static void sha256_szmax_upd(SHA256_t *ps256, mem_t *data, ucnum len)
 {
-  SHA256_t s256;
-  SHA256_init(&s256);
-  ucnum len = c_unum(buf->b.len);
-  mem_t *data = buf->b.data;
   const size_t szmax = convert(size_t, -1) / 4 + 1;
-
   while (len >= szmax) {
-    SHA256_update(&s256, data, szmax);
+    SHA256_update(ps256, data, szmax);
     data += szmax;
     len -= szmax;
   }
-
   if (len > 0)
-    SHA256_update(&s256, data, len);
+    SHA256_update(ps256, data, len);
+}
 
+static void sha256_buf(val buf, unsigned char *hash)
+{
+  SHA256_t s256;
+  SHA256_init(&s256);
+  sha256_szmax_upd(&s256, buf->b.data, c_unum(buf->b.len));
   SHA256_final(&s256, hash);
 }
 
@@ -199,7 +199,7 @@ val sha256_hash(val ctx, val obj)
     }
     break;
   case BUF:
-    SHA256_update(ps256, obj->b.data, c_unum(obj->b.len));
+    sha256_szmax_upd(ps256, obj->b.data, c_unum(obj->b.len));
     break;
   default:
     uw_throwf(error_s, lit("~a: cannot hash ~s, only buffer and strings"),
@@ -360,23 +360,23 @@ val md5_stream(val stream, val nbytes, val buf_in)
   return buf;
 }
 
-static void md5_buf(val buf, unsigned char *hash)
+static void md5_szmax_upd(MD5_t *pmd5, mem_t *data, ucnum len)
 {
-  MD5_t md5;
-  MD5_init(&md5);
-  ucnum len = c_unum(buf->b.len);
-  mem_t *data = buf->b.data;
   const size_t szmax = convert(size_t, -1) / 4 + 1;
-
   while (len >= szmax) {
-    MD5_update(&md5, data, szmax);
+    MD5_update(pmd5, data, szmax);
     data += szmax;
     len -= szmax;
   }
-
   if (len > 0)
-    MD5_update(&md5, data, len);
+    MD5_update(pmd5, data, len);
+}
 
+static void md5_buf(val buf, unsigned char *hash)
+{
+  MD5_t md5;
+  MD5_init(&md5);
+  md5_szmax_upd(&md5, buf->b.data, c_unum(buf->b.len));
   MD5_final(&md5, hash);
 }
 
@@ -440,7 +440,7 @@ val md5_hash(val ctx, val obj)
     }
     break;
   case BUF:
-    MD5_update(pmd5, obj->b.data, c_unum(obj->b.len));
+    md5_szmax_upd(pmd5, obj->b.data, c_unum(obj->b.len));
     break;
   default:
     uw_throwf(error_s, lit("~a: cannot hash ~s, only buffer and strings"),
-- 
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