sha1dc: integrate the sha1dc code with the git buildlt/sha1dc

This adds the proper magic to actually build the sha1dc code as part
of git when USE_SHA1DC is enabled.

This includes

 - adjusting the sha1dc include directives for git use

 - adding the proper USE_SHA1DC logic to the Makefile

 - adding the SHA1DC case to the "hash.h" header

 - adding the proper "git platform" wrappers for the SHA1 interface

Much of this comes from Jeff King's previous integration effort, with
modifications for the new world order of hash.h.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

6 files changed, 55 insertions, 14 deletions

diff --git a/Makefile b/Makefile
index 25c21f08b1..b1cb652e34 100644
--- a/Makefile
+++ b/Makefile
@@ -142,6 +142,10 @@ all::
 # Define PPC_SHA1 environment variable when running make to make use of
 # a bundled SHA1 routine optimized for PowerPC.
 #
+# Define USE_SHA1DC to unconditionally enable the collision-detecting sha1
+# algorithm. This is slower, but may detect attempted collision attacks.
+# Takes priority over other *_SHA1 knobs.
+#
 # Define SHA1_MAX_BLOCK_SIZE to limit the amount of data that will be hashed
 # in one call to the platform's SHA1_Update(). e.g. APPLE_COMMON_CRYPTO
 # wants 'SHA1_MAX_BLOCK_SIZE=1024L*1024L*1024L' defined.
@@ -1386,6 +1390,11 @@ ifdef APPLE_COMMON_CRYPTO
 	SHA1_MAX_BLOCK_SIZE = 1024L*1024L*1024L
 endif
 
+ifdef USE_SHA1DC
+	LIB_OBJS += sha1dc/sha1.o
+	LIB_OBJS += sha1dc/ubc_check.o
+	BASIC_CFLAGS += -DSHA1DC
+else
 ifdef BLK_SHA1
 	LIB_OBJS += block-sha1/sha1.o
 	BASIC_CFLAGS += -DSHA1_BLK
@@ -1403,6 +1412,7 @@ else
 endif
 endif
 endif
+endif
 
 ifdef SHA1_MAX_BLOCK_SIZE
 	LIB_OBJS += compat/sha1-chunked.o
diff --git a/hash.h b/hash.h
index f0d9ddd0c2..b9e7e34fcd 100644
--- a/hash.h
+++ b/hash.h
@@ -3,6 +3,8 @@
 
 #if defined(SHA1_PPC)
 #include "ppc/sha1.h"
+#elif defined(SHA1DC)
+#include "sha1dc/sha1.h"
 #elif defined(SHA1_APPLE)
 #include <CommonCrypto/CommonDigest.h>
 #elif defined(SHA1_OPENSSL)
diff --git a/sha1dc/sha1.c b/sha1dc/sha1.c
index 27a535c6a7..6c984215bd 100644
--- a/sha1dc/sha1.c
+++ b/sha1dc/sha1.c
@@ -5,14 +5,9 @@
 * https://opensource.org/licenses/MIT
 ***/
 
-#include <string.h>
-#include <memory.h>
-#include <stdio.h>
-#include <stdlib.h>
-
-#include "sha1.h"
-#include "ubc_check.h"
-
+#include "git-compat-util.h"
+#include "sha1dc/sha1.h"
+#include "sha1dc/ubc_check.h"
 
 /*
    Because Little-Endian architectures are most common,
@@ -1790,3 +1785,25 @@ int SHA1DCFinal(unsigned char output[20], SHA1_CTX *ctx)
 	output[19] = (unsigned char)(ctx->ihv[4]);
 	return ctx->found_collision;
 }
+
+static const char collision_message[] =
+"The SHA1 computation detected evidence of a collision attack;\n"
+"refusing to process the contents.";
+
+void git_SHA1DCFinal(unsigned char hash[20], SHA1_CTX *ctx)
+{
+	if (SHA1DCFinal(hash, ctx))
+		die(collision_message);
+}
+
+void git_SHA1DCUpdate(SHA1_CTX *ctx, const void *vdata, unsigned long len)
+{
+	const char *data = vdata;
+	/* We expect an unsigned long, but sha1dc only takes an int */
+	while (len > INT_MAX) {
+		SHA1DCUpdate(ctx, data, INT_MAX);
+		data += INT_MAX;
+		len -= INT_MAX;
+	}
+	SHA1DCUpdate(ctx, data, len);
+}
diff --git a/sha1dc/sha1.h b/sha1dc/sha1.h
index 88556179b5..84d6f143e1 100644
--- a/sha1dc/sha1.h
+++ b/sha1dc/sha1.h
@@ -9,8 +9,6 @@
 extern "C" {
 #endif
 
-#include <stdint.h>
-
 /* uses SHA-1 message expansion to expand the first 16 words of W[] to 80 words */
 /* void sha1_message_expansion(uint32_t W[80]); */
 
@@ -100,6 +98,22 @@ void SHA1DCUpdate(SHA1_CTX*, const char*, size_t);
 /* returns: 0 = no collision detected, otherwise = collision found => warn user for active attack */
 int  SHA1DCFinal(unsigned char[20], SHA1_CTX*);
 
+
+/*
+ * Same as SHA1DCFinal, but convert collision attack case into a verbose die().
+ */
+void git_SHA1DCFinal(unsigned char [20], SHA1_CTX *);
+
+/*
+ * Same as SHA1DCUpdate, but adjust types to match git's usual interface.
+ */
+void git_SHA1DCUpdate(SHA1_CTX *ctx, const void *data, unsigned long len);
+
+#define platform_SHA_CTX SHA1_CTX
+#define platform_SHA1_Init SHA1DCInit
+#define platform_SHA1_Update git_SHA1DCUpdate
+#define platform_SHA1_Final git_SHA1DCFinal
+
 #if defined(__cplusplus)
 }
 #endif
diff --git a/sha1dc/ubc_check.c b/sha1dc/ubc_check.c
index 27d0976daa..089dd4743d 100644
--- a/sha1dc/ubc_check.c
+++ b/sha1dc/ubc_check.c
@@ -24,8 +24,8 @@
 // ubc_check has been verified against ubc_check_verify using the 'ubc_check_test' program in the tools section
 */
 
-#include <stdint.h>
-#include "ubc_check.h"
+#include "git-compat-util.h"
+#include "sha1dc/ubc_check.h"
 
 static const uint32_t DV_I_43_0_bit 	= (uint32_t)(1) << 0;
 static const uint32_t DV_I_44_0_bit 	= (uint32_t)(1) << 1;
diff --git a/sha1dc/ubc_check.h b/sha1dc/ubc_check.h
index b349bed928..b64c306d77 100644
--- a/sha1dc/ubc_check.h
+++ b/sha1dc/ubc_check.h
@@ -27,8 +27,6 @@
 extern "C" {
 #endif
 
-#include <stdint.h>
-
 #define DVMASKSIZE 1
 typedef struct { int dvType; int dvK; int dvB; int testt; int maski; int maskb; uint32_t dm[80]; } dv_info_t;
 extern dv_info_t sha1_dvs[];