initial checking

This is a rewrite of ssdeep's fuzzy.c to do streaming hashes. It is a
bit slower, but the memory consumption is bounded in all cases.

1 files changed, 375 insertions, 0 deletions

diff --git a/fuzzy.c b/fuzzy.c
new file mode 100644
index 0000000..7b2b608
--- /dev/null
+++ b/fuzzy.c
@@ -0,0 +1,375 @@
+/* ssdeep
+ * Copyright (C) 2002 Andrew Tridgell <tridge@samba.org>
+ * Copyright (C) 2006 ManTech International Corporation
+ * Copyright (C) 2013 Helmut Grohne <helmut@subdivi.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Earlier versions of this code were named fuzzy.c and can be found at:
+ *     http://www.samba.org/ftp/unpacked/junkcode/spamsum/
+ *     http://ssdeep.sf.net/
+ */
+
+#include <assert.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#if defined(__GNUC__) && __GNUC__ >= 3
+#define likely(x)       __builtin_expect(!!(x), 1)
+#define unlikely(x)     __builtin_expect(!!(x), 0)
+#else
+#define likely(x) x
+#define unlikely(x) x
+#endif
+
+#define SPAMSUM_LENGTH 64
+#define FUZZY_MAX_RESULT (SPAMSUM_LENGTH + (SPAMSUM_LENGTH/2 + 20))
+#define ROLLING_WINDOW 7
+#define MIN_BLOCKSIZE 3
+#define HASH_PRIME 0x01000193
+#define HASH_INIT 0x28021967
+
+struct roll_state {
+	unsigned char window[ROLLING_WINDOW];
+	uint32_t h1, h2, h3;
+	uint32_t n;
+};
+
+static void roll_init(/*@out@*/ struct roll_state *self) {
+	memset(self, 0, sizeof(struct roll_state));
+}
+
+/*
+ * a rolling hash, based on the Adler checksum. By using a rolling hash
+ * we can perform auto resynchronisation after inserts/deletes
+
+ * internally, h1 is the sum of the bytes in the window and h2
+ * is the sum of the bytes times the index
+
+ * h3 is a shift/xor based rolling hash, and is mostly needed to ensure that
+ * we can cope with large blocksize values
+ */
+static void roll_hash(struct roll_state *self, unsigned char c) {
+	self->h2 -= self->h1;
+ 	self->h2 += ROLLING_WINDOW * (uint32_t)c;
+
+	self->h1 += (uint32_t)c;
+	self->h1 -= (uint32_t)self->window[self->n % ROLLING_WINDOW];
+
+	self->window[self->n % ROLLING_WINDOW] = c;
+	self->n++;
+
+	/* The original spamsum AND'ed this value with 0xFFFFFFFF which
+	 * in theory should have no effect. This AND has been removed
+	 * for performance (jk) */
+	self->h3 <<= 5;
+ 	self->h3 ^= c;
+}
+
+static uint32_t roll_sum(const struct roll_state *self) {
+	return self->h1 + self->h2 + self->h3;
+}
+
+/* A simple non-rolling hash, based on the FNV hash. */
+static uint32_t sum_hash(unsigned char c, uint32_t h) {
+	return (h * HASH_PRIME) ^ c;
+}
+
+/* A blockhash contains a signature state for a specific (implicit) blocksize.
+ * The blocksize is given by the start_blocksize from ssdeep_context times two
+ * to the power of the position of the element in the blockhashes member of
+ * ssdeep_context (head position = 0). The h and halfh members are the FNV
+ * hashes, where halfh stops to be reset after digest is SPAMSUM_LENGTH/2 long.
+ * The halfh hash is needed be able to truncate digest for the second output
+ * hash to stay compatible with ssdeep output. */
+struct blockhash_context {
+	uint32_t h, halfh;
+	char digest[SPAMSUM_LENGTH];
+	unsigned int dlen;
+	/*@null@*/ struct blockhash_context *next;
+};
+
+struct ssdeep_context {
+	unsigned int start_blocksize;
+	struct blockhash_context *blockhashes;
+	size_t total_size;
+	struct roll_state roll;
+};
+
+static int ssdeep_init(/*@out@*/ struct ssdeep_context *self) {
+	self->blockhashes = malloc(sizeof(struct blockhash_context));
+	if(NULL == self->blockhashes)
+		return -1;
+	self->start_blocksize = MIN_BLOCKSIZE;
+	self->blockhashes->h = HASH_INIT;
+	self->blockhashes->halfh = HASH_INIT;
+	self->blockhashes->dlen = 0;
+	self->blockhashes->next = NULL;
+	self->total_size = 0;
+	roll_init(&self->roll);
+	return 0;
+}
+
+static const char *b64 =
+	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+static int ssdeep_engine_step(struct ssdeep_context *self, unsigned char c) {
+	size_t h;
+	unsigned int bs;
+	struct blockhash_context *bh;
+	/* At each character we update the rolling hash and the normal hashes.
+	 * When the rolling hash hits a reset value then we emit a normal hash
+	 * as a element of the signature and reset the normal hash. */
+	roll_hash(&self->roll, c);
+	h = roll_sum(&self->roll);
+
+	for(bh = self->blockhashes; NULL != bh; bh = bh->next) {
+		bh->h = sum_hash(c, bh->h);
+		bh->halfh = sum_hash(c, bh->halfh);
+	}
+
+	bs = self->start_blocksize;
+	bh = self->blockhashes;
+	while(bh != NULL) {
+		/* With growing blocksize almost no runs fail the next test. */
+		if(likely(h % bs != bs - 1))
+			/* Once this condition is false for one bs, it is
+			 * automatically false for all further bs. I.e. if
+			 * h === -1 (mod 2*bs) then h === -1 (mod bs). */
+			break;
+		/* We don't need bs until next iteration. Update now, so we
+		 * don't forget about it. */
+		bs *= 2;
+		/* We have hit a reset point. We now emit hashes which are
+		 * based on all characters in the piece of the message between
+		 * the last reset point and this one */
+		if(unlikely(0 == bh->dlen)) { /* Can only happen 30 times. */
+			/* First step for this blocksize. Clone next. */
+			assert(NULL == bh->next);
+			bh->next = malloc(sizeof(
+					struct blockhash_context));
+			if(NULL == bh->next)
+				return -1;
+			bh->next->h = bh->h;
+			bh->next->dlen = 0;
+			bh->next->next = NULL;
+		}
+		if(bh->dlen < SPAMSUM_LENGTH - 1) {
+			/* We can have a problem with the tail overflowing. The
+			 * easiest way to cope with this is to only reset the
+			 * normal hash if we have room for more characters in
+			 * our signature. This has the effect of combining the
+			 * last few pieces of the message into a single piece
+			 * */
+			bh->digest[bh->dlen++] = b64[bh->h % 64];
+			bh->h = HASH_INIT;
+			if(bh->dlen < SPAMSUM_LENGTH / 2)
+				bh->halfh = HASH_INIT;
+		} else if(NULL != bh->next &&
+				(size_t)self->start_blocksize * SPAMSUM_LENGTH <
+					self->total_size &&
+				bh->next->dlen >= SPAMSUM_LENGTH / 2 &&
+				bh == self->blockhashes) {
+			/* Operating on the currently smallest blocksize and
+			 * the next blocksize is already large enough. */
+			self->start_blocksize *= 2;
+			bh = bh->next;
+			free(self->blockhashes);
+			self->blockhashes = bh;
+			continue;
+		}
+		bh = bh->next;
+	}
+	++self->total_size;
+	return 0;
+}
+
+static int ssdeep_engine(struct ssdeep_context *self,
+		const unsigned char *buffer, size_t buffer_size) {
+	for( ;buffer_size > 0; ++buffer, --buffer_size)
+		if(ssdeep_engine_step(self, *buffer) < 0)
+			return -1;
+	return 0;
+}
+
+static void ssdeep_digest(const struct ssdeep_context *self,
+		/*@out@*/ char *result) {
+	unsigned int bs = self->start_blocksize;
+	uint32_t h = roll_sum(&self->roll);
+	int i, remain = FUZZY_MAX_RESULT - 1;
+	const struct blockhash_context *bh = self->blockhashes, *bhp;
+	/* Verify that our elimination was not overeager. */
+	assert(bs == MIN_BLOCKSIZE ||
+			(size_t)bs / 2 * SPAMSUM_LENGTH < self->total_size);
+
+	/* Initial blocksize guess. */
+	while((size_t)bs * SPAMSUM_LENGTH < self->total_size) {
+		bs *= 2;
+		assert(bh->next != NULL);
+		bh = bh->next;
+	}
+	/* Adapt blocksize guess to actual digest length. */
+	while(bs > self->start_blocksize && bh->dlen < SPAMSUM_LENGTH / 2) {
+		bs /= 2;
+		/* Slow version of bh = bh->prev; */
+		for(bhp = self->blockhashes; bhp->next != bh; bhp = bhp->next)
+			;
+		bh = bhp;
+	}
+	assert(bh != NULL);
+	assert(!(bs > MIN_BLOCKSIZE && bh->dlen < SPAMSUM_LENGTH / 2));
+
+	i = snprintf(result, (size_t)remain, "%u:", bs);
+	/* In theory snprintf can fail. It is unclear how though, so we assume
+	 * that it doesn't for simplicity. */
+	assert(i > 0);
+	assert(i < remain);
+	remain -= i;
+	result += i;
+	i = (int)bh->dlen;
+	if(i > remain)
+		i = remain;
+	memcpy(result, bh->digest, (size_t)i);
+	result += i;
+	remain -= i;
+	if(remain > 0 && h != 0) {
+		*result++ = b64[bh->h % 64];
+		--remain;
+	}
+	if(remain > 0) {
+		*result++ = ':';
+		--remain;
+	}
+	if(NULL != bh->next) {
+		bh = bh->next;
+		i = (int)bh->dlen;
+		if(i > SPAMSUM_LENGTH / 2 - 1)
+			i = SPAMSUM_LENGTH / 2 - 1;
+		if(i > remain)
+			i = remain;
+		memcpy(result, bh->digest, (size_t)i);
+		result += i;
+		remain -= i;
+		if(remain > 0 && h != 0) {
+			*result++ = b64[bh->halfh % 64];
+			--remain;
+		}
+	} else if(remain > 0 && h != 0) {
+		assert(bh->dlen == 0);
+		*result++ = b64[bh->h % 64];
+		--remain;
+	}
+	*result = '\0';
+}
+
+static void ssdeep_clear(struct ssdeep_context *self) {
+	struct blockhash_context *bh, *bhn;
+	bh = self->blockhashes;
+	while(bh) {
+		bhn = bh->next;
+		free(bh);
+		bh = bhn;
+	}
+}
+
+int fuzzy_hash_buf(const unsigned char *buf, uint32_t buf_len,
+		/*@out@*/ char *result) {
+	struct ssdeep_context ctx[1];
+	if(ssdeep_init(ctx) < 0)
+		return -1;
+	if(ssdeep_engine(ctx, buf, buf_len) < 0) {
+		ssdeep_clear(ctx);
+		return -1;
+	}
+	ssdeep_digest(ctx, result);
+	ssdeep_clear(ctx);
+	return 0;
+}
+
+int fuzzy_hash_stream(FILE *handle, /*@out@*/ char *result) {
+	struct ssdeep_context ctx[1];
+	unsigned char buffer[4096];
+	size_t n;
+	if(ssdeep_init(ctx) < 0)
+		return -1;
+	for(;;) {
+		n = fread(buffer, 1, 4096, handle);
+		if(0 == n)
+			break;
+		if(ssdeep_engine(ctx, buffer, n) < 0)
+			goto errout;
+	}
+	if(ferror(handle) != 0)
+		goto errout;
+	ssdeep_digest(ctx, result);
+	ssdeep_clear(ctx);
+	return 0;
+errout:
+	ssdeep_clear(ctx);
+	return -1;
+}
+
+#ifdef S_SPLINT_S
+typedef size_t off_t;
+#endif
+
+int fuzzy_hash_file(FILE *handle, /*@out@*/ char *result) {
+	off_t fpos;
+	int status;
+	fpos = ftello(handle);
+	if(fseek(handle, 0, SEEK_SET) < 0)
+		return -1;
+	status = fuzzy_hash_stream(handle, result);
+	if(status == 0)
+		if(fseeko(handle, fpos, SEEK_SET) < 0)
+			return -1;
+	return status;
+}
+
+int fuzzy_hash_filename(const char *filename, /*@out@*/ char *result) {
+	int status;
+	FILE *handle = fopen(filename, "rb");
+	if(NULL == handle)
+		return -1;
+	status = fuzzy_hash_file(handle, result);
+	/* We cannot do anything about an fclose failure. */
+	(void)fclose(handle);
+	return status;
+}
+
+#ifdef S_SPLINT_S
+extern /*@only@*/ /*@null@*/ char *realpath(const char *,
+		/*@null@*/ const char *);
+#endif
+
+int main(int argc, char **argv) {
+	char digest[FUZZY_MAX_RESULT], *p;
+	int i;
+	puts("ssdeep,1.1--blocksize:hash:hash,filename");
+	for(i = 1; i < argc; ++i) {
+		p = realpath(argv[i], NULL);
+		if(p == NULL)
+			return 1;
+		if(fuzzy_hash_filename(argv[i], digest) < 0) {
+			free(p);
+			return 1;
+		}
+		printf("%s,\"%s\"\n", digest, p);
+		free(p);
+	}
+	return 0;
+}