Merge pull request #314 from nrclark/randomseed

config: add new randomseed option

Author: michaelolbrich

Makefile.am

@@ -18,6 +18,7 @@ genimage_SOURCES = \
 	config.c \
 	util.c \
 	crc32.c \
+	random32.c \
 	image-android-sparse.c \
 	image-cpio.c \
 	image-cramfs.c \
@@ -152,6 +153,8 @@ EXTRA_DIST += \
 	test/mke2fs.3.dump \
 	test/qemu.config \
 	test/qemu.qcow.gz \
+	test/randomseed.config \
+	test/randomseed.expected \
 	test/rauc.config \
 	test/sharness.sh \
 	test/signing-ca/ca.cert.pem \

README.rst

@@ -791,7 +791,8 @@ variable.
 
 :loglevel:	default: 1
 		genimage log level.
-
+:randomseed:	default: none
+		Random number generator seed (optional).
 :outputpath:	default: images
 		Mandatory path where all images are written to (must exist).
 :inputpath:	default: input

config.c

@@ -489,6 +489,12 @@ static struct config opts[] = {
 		.env = "GENIMAGE_QEMU",
 		.def = "qemu-img",
 	},
+	{
+		.name = "randomseed",
+		.opt = CFG_STR("randomseed", NULL, CFGF_NONE),
+		.env = "GENIMAGE_RANDOMSEED",
+		.def = NULL,
+	},
 	{
 		.name = "rauc",
 		.opt = CFG_STR("rauc", NULL, CFGF_NONE),

genimage.c

@@ -21,7 +21,6 @@
 #include <errno.h>
 #include <libgen.h>
 #include <sys/stat.h>
-#include <sys/time.h>
 #include <sys/types.h>
 #include <dirent.h>
 
@@ -700,11 +699,6 @@ int main(int argc, char *argv[])
 	cfg_opt_t image_end[] = {
 		CFG_END()
 	};
-	struct timeval tv;
-
-	/* Seed the rng */
-	gettimeofday(&tv, NULL);
-	srandom(tv.tv_usec);
 
 	memcpy(imageopts, image_common_opts, sizeof(image_common_opts));
 
@@ -760,6 +754,13 @@ int main(int argc, char *argv[])
 	/* again, with config file this time */
 	set_config_opts(argc, argv, cfg);
 
+	str = get_opt("randomseed");
+	if (!str || (*str == '\0')) {
+		random32_init();
+	} else {
+		random32_enable_prng(str, strnlen(str, 4096));
+	}
+
 	str = get_opt("configdump");
 	if (str) {
 		FILE *dump;

genimage.h

@@ -225,4 +225,8 @@ uint32_t crc32_next(const void *data, size_t len, uint32_t last_crc);
 
 #define ct_assert(e) _Static_assert(e, #e)
 
+void random32_init(void);
+void random32_enable_prng(const char *seed, size_t length);
+uint32_t random32(void);
+
 #endif /* __PTX_IMAGE_H */

image-hd.c

@@ -871,7 +871,7 @@ static int setup_uuid(struct image *image, cfg_t *cfg)
 	if (!disk_signature)
 		hd->disksig = 0;
 	else if (!strcmp(disk_signature, "random"))
-		hd->disksig = random();
+		hd->disksig = random32();
 	else {
 		if (!(hd->table_type & TYPE_MBR)) {
 			image_error(image, "'disk-signature' is only valid for mbr and hybrid partition-table-type\n");

random32.c

@@ -0,0 +1,87 @@
+/*
+ * 32-bit xorwow-based PRNG with a seed input. Based on George Marsaglia's
+ * Xorshift RNGs paper.
+ *
+ * Copyright (c) 2025 Nicholas Clark <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <sys/time.h>
+
+#include "genimage.h"
+
+struct prng_state {
+	uint32_t lane[5];
+	uint32_t counter;
+};
+
+static uint32_t prng_getrandom(struct prng_state *state)
+{
+	uint32_t buffer = state->lane[4];
+
+	state->lane[4] = state->lane[3];
+	state->lane[3] = state->lane[2];
+	state->lane[2] = state->lane[1];
+	state->lane[1] = state->lane[0];
+
+	buffer ^= buffer >> 2;
+	buffer ^= buffer << 1;
+	buffer ^= state->lane[0] ^ (state->lane[0] << 4);
+	state->lane[0] = buffer;
+	state->counter += 0x587C5;
+
+	return buffer + state->counter;
+}
+
+static void prng_seed(struct prng_state *state, uint32_t seed)
+{
+	state->counter = seed;
+	state->lane[0] = 1 + (seed & 0x0FFFFFFFu);
+	state->lane[1] = 2 + (seed & 0xFF0FFFFFu);
+	state->lane[2] = 3 + (seed & 0xFFF00FFFu);
+	state->lane[3] = 4 + (seed & 0xFFFFF0FFu);
+	state->lane[4] = 5 + (seed & 0xFFFFFFF0u);
+
+	for (int x = 0; x < 8; x++) {
+		prng_getrandom(state);
+	}
+}
+
+static struct prng_state prng = { { 1, 2, 3, 4, 5 }, 0 };
+static bool prng_active = false;
+
+void random32_init(void)
+{
+	struct timeval tv;
+	gettimeofday(&tv, NULL);
+	srandom(tv.tv_usec);
+	prng_active = false;
+}
+
+void random32_enable_prng(const char *seed, size_t length)
+{
+	prng_seed(&prng, crc32(seed, length));
+	prng_active = true;
+}
+
+uint32_t random32(void)
+{
+	if (prng_active) {
+		return prng_getrandom(&prng);
+	}
+	return random();
+}

test/misc.test

@@ -143,6 +143,30 @@ test_expect_success "custom" "
 	echo 'Hello genimage!' > images/test.custom.expect &&
 	test_cmp images/test.custom.expect images/test.custom
 "
+test_expect_success "disable random-seed" "
+	extra_opts="--randomseed=" &&
+	run_genimage randomseed.config randomseed.img &&
+	hexdump -C images/randomseed.img > randomseed.expected &&
+	unset extra_opts &&
+	test_must_fail diff -q $SHARNESS_TEST_SRCDIR/randomseed.expected randomseed.expected
+"
+
+test_expect_success "enable random-seed" "
+	run_genimage randomseed.config randomseed.img &&
+		hexdump -C images/randomseed.img > randomseed.expected &&
+	diff -q $SHARNESS_TEST_SRCDIR/randomseed.expected randomseed.expected
+"
+
+test_expect_success "use different random-seeds" "
+		extra_opts="--randomseed=2" &&
+		run_genimage randomseed.config randomseed.img &&
+		hexdump -C images/randomseed.img > randomseed.expected.1 &&
+		extra_opts="--randomseed=3" &&
+		run_genimage randomseed.config randomseed.img &&
+		hexdump -C images/randomseed.img > randomseed.expected.2 &&
+		unset extra_opts &&
+		test_must_fail diff -q randomseed.expected.1 randomseed.expected.2
+"
 
 exec_test_set_prereq base64
 exec_test_set_prereq dd

test/randomseed.config

@@ -0,0 +1,13 @@
+image randomseed.img {
+    hdimage {
+        partition-table-type = "gpt"
+    }
+
+    partition rootfs {
+        size = 1M
+    }
+}
+
+config {
+    randomseed = 1
+}

test/randomseed.expected

@@ -0,0 +1,37 @@
+00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+*
+000001c0  02 00 ee 21 29 00 01 00  00 00 47 08 00 00 00 00  |...!).....G.....|
+000001d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+*
+000001f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 55 aa  |..............U.|
+00000200  45 46 49 20 50 41 52 54  00 00 01 00 5c 00 00 00  |EFI PART....\...|
+00000210  a8 9f e4 6e 00 00 00 00  01 00 00 00 00 00 00 00  |...n............|
+00000220  47 08 00 00 00 00 00 00  22 00 00 00 00 00 00 00  |G.......".......|
+00000230  26 08 00 00 00 00 00 00  18 07 21 30 00 55 81 53  |&.........!0.U.S|
+00000240  ff 99 08 fd 68 07 00 40  02 00 00 00 00 00 00 00  |....h..@........|
+00000250  80 00 00 00 80 00 00 00  e5 81 84 df 00 00 00 00  |................|
+00000260  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+*
+00000400  af 3d c6 0f 83 84 72 47  8e 79 3d 69 d8 47 7d e4  |.=....rG.y=i.G}.|
+00000410  62 09 50 60 00 40 99 61  ff 94 03 fd 88 82 00 46  |b.P`[email protected]|
+00000420  22 00 00 00 00 00 00 00  21 08 00 00 00 00 00 00  |".......!.......|
+00000430  00 00 00 00 00 00 00 00  72 00 6f 00 6f 00 74 00  |........r.o.o.t.|
+00000440  66 00 73 00 00 00 00 00  00 00 00 00 00 00 00 00  |f.s.............|
+00000450  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+*
+00104e00  af 3d c6 0f 83 84 72 47  8e 79 3d 69 d8 47 7d e4  |.=....rG.y=i.G}.|
+00104e10  62 09 50 60 00 40 99 61  ff 94 03 fd 88 82 00 46  |b.P`[email protected]|
+00104e20  22 00 00 00 00 00 00 00  21 08 00 00 00 00 00 00  |".......!.......|
+00104e30  00 00 00 00 00 00 00 00  72 00 6f 00 6f 00 74 00  |........r.o.o.t.|
+00104e40  66 00 73 00 00 00 00 00  00 00 00 00 00 00 00 00  |f.s.............|
+00104e50  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+*
+00108e00  45 46 49 20 50 41 52 54  00 00 01 00 5c 00 00 00  |EFI PART....\...|
+00108e10  e3 54 c1 02 00 00 00 00  47 08 00 00 00 00 00 00  |.T......G.......|
+00108e20  01 00 00 00 00 00 00 00  22 00 00 00 00 00 00 00  |........".......|
+00108e30  26 08 00 00 00 00 00 00  18 07 21 30 00 55 81 53  |&.........!0.U.S|
+00108e40  ff 99 08 fd 68 07 00 40  27 08 00 00 00 00 00 00  |....h..@'.......|
+00108e50  80 00 00 00 80 00 00 00  e5 81 84 df 00 00 00 00  |................|
+00108e60  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+*
+00109000