feat(seedrng): use it

Signed-off-by: Raito Bezarius <masterancpp@gmail.com>

.forgejo/workflows/build.yaml

@@ -38,13 +38,3 @@ jobs:
         run: |
           # Enter the shell
           nix-build ci.nix -A wlan
-
-  test_shell_customization:
-    runs-on: nix
-    steps:
-      - uses: actions/checkout@v3
-
-      - name: Build VM QEMU MIPS
-        run: |
-          # Enter the shell
-          nix-build ci.nix -A custom-shell

modules/base.nix

@@ -4,13 +4,11 @@
 
 { lib, pkgs, config, ...}:
 let
-  inherit (lib) mkEnableOption mkOption types isDerivation hasAttr concatStringsSep mapAttrsToList;
+  inherit (lib) mkEnableOption mkOption types isDerivation hasAttr ;
   inherit (pkgs.pseudofile) dir symlink;
   inherit (pkgs.liminix.networking) address interface;
   inherit (pkgs.liminix.services) bundle;
 
-  # TODO: escape shell argument.
-  exportVar = name: value: "export ${name}=\"${value}\"";
   type_service = pkgs.liminix.lib.types.service;
 
 in {
@@ -24,24 +22,6 @@ in {
           /run/current-system, we just add the paths in /etc/profile
         '';
       };
-
-      environmentVariables = mkOption {
-        type = types.attrsOf types.str;
-        description = ''
-          Attribute set of environment variables to make available
-          in a login shell.
-
-          The value is assumed to be escaped and the name to be valid.
-        '';
-      };
-
-      prompt = mkOption {
-        type = types.str;
-        default = "$(whoami)@$(hostname) # ";
-        description = ''
-          Prompt string (PS1) for the shell.
-        '';
-      };
     };
     services = mkOption {
       type = types.attrsOf type_service;
@@ -131,8 +111,6 @@ in {
 
     defaultProfile.packages = with pkgs;
       [ s6 s6-init-bin execline s6-linux-init s6-rc ];
-    # Set the useful PS1 prompt by default.
-    defaultProfile.environmentVariables.PS1 = lib.mkDefault config.defaultProfile.prompt;
 
     boot.commandLine = [
       "panic=10 oops=panic init=/bin/init loglevel=8"
@@ -205,7 +183,6 @@ in {
           (pkgs.writeScript ".profile" ''
            PATH=${lib.makeBinPath config.defaultProfile.packages}:/bin
             export PATH
-            ${concatStringsSep "\n" (mapAttrsToList exportVar config.defaultProfile.environmentVariables)}
             '');
       in dir {
         inherit profile;

modules/hostname.nix

@@ -1,6 +1,7 @@
 { lib, pkgs, config, ...}:
 let
   inherit (lib) mkOption types;
+  inherit (pkgs.liminix.services) oneshot;
 in {
   options = {
     hostname = mkOption {
@@ -11,21 +12,12 @@ in {
       default = "liminix";
       type = types.nonEmptyStr;
     };
-    hostname-script = mkOption {
+  };
-      description = ''
+  config = {
-        Script that outputs the system hostname on stdin.
+    services.hostname = oneshot {
-      '';
+      name = "hostname-${builtins.substring 0 12 (builtins.hashString "sha256" config.hostname)}";
-      default = pkgs.writeScript "hostname-gen" ''
+      up = "echo ${config.hostname} > /proc/sys/kernel/hostname";
-        #!/bin/sh
+      down = "true";
-        echo ${config.hostname}
-      '';
-      defaultText = ''
-        pkgs.writeScript "hostname-gen" '''
-        #!/bin/sh
-        echo ''${config.hostname}
-      '''
-      '';
-      type = types.package;
     };
   };
 }

modules/s6/default.nix

@@ -1,4 +1,4 @@
-{ config, pkgs, ... }:
+{ config, pkgs, lib, ... }:
 let
   inherit (pkgs)
     execline
@@ -30,9 +30,9 @@ let
     installPhase = ''
       mkdir $out
       cp -r $src $out/scripts
-      substituteInPlace $out/scripts/rc.init \
-        --replace-fail 'config.hostname' "${config.hostname-script}"
       chmod -R +w $out
+      substituteInPlace $out/scripts/{rc.init,rc.shutdown} \
+        --replace-warn 'pkgs.seedrng' "${lib.getExe' pkgs.seedrng "seedrng"}"
     '';
   };
   service = dir  {

modules/s6/scripts/rc.init

@@ -32,11 +32,12 @@ else
     mkdir -m 0751 -p /run/services/state
 fi
 
+pkgs.seedrng
+
 ### If your services are managed by s6-rc:
 ### (replace /run/service with your scandir)
 s6-rc-init -d -c /etc/s6-rc/compiled /run/service
 
-config.hostname > /proc/sys/kernel/hostname
 
 ### 2. Starting the wanted set of services
 ### This is also called every time you change runlevels with telinit.

modules/s6/scripts/rc.shutdown

@@ -4,6 +4,7 @@
 ### Things to do before hardware halt/reboot/poweroff.
 ### Ideally, it should be a single call to the service manager,
 ### telling it to bring all the services down.
+pkgs.seedrng
 
 ### If your s6-linux-init-maker invocation was made with the -1
 ### option, messages from rc.shutdown will appear on /dev/console

pkgs/default.nix

@@ -99,6 +99,7 @@ in {
   run-liminix-vm = callPackage ./run-liminix-vm {};
   s6-init-bin =  callPackage ./s6-init-bin {};
   s6-rc-database = callPackage ./s6-rc-database {};
+  seedrng = callPackage ./seedrng {};
 
   # schnapps is written by Turris and provides a high-level interface
   # to btrfs snapshots. It may be useful on the Turris Omnia to

pkgs/seedrng/COPYING

@@ -0,0 +1,712 @@
+This project is licensed under any one of:
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+- MIT
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+- CC0-1.0
+
+Choose which one works best for you. They are reproduced below.
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pkgs/seedrng/Makefile

@@ -0,0 +1,18 @@
+PREFIX ?= /usr
+DESTDIR ?=
+SBINDIR ?= $(PREFIX)/sbin
+LOCALSTATEDIR ?= /var/lib
+CFLAGS ?= -O2 -pipe
+
+CFLAGS += -Wall -Wextra -pedantic
+CFLAGS += -DLOCALSTATEDIR="\"$(LOCALSTATEDIR)\""
+
+seedrng: seedrng.c
+
+install: seedrng
+	install -v -d "$(DESTDIR)$(SBINDIR)" && install -v -m 0755 seedrng "$(DESTDIR)$(SBINDIR)/seedrng"
+
+clean:
+	rm -f seedrng
+
+.PHONY: clean

pkgs/seedrng/README.md

@@ -0,0 +1,72 @@
+## SeedRNG — `seedrng(8)`
+##### by [Jason A. Donenfeld](mailto:Jason@zx2c4.com)
+
+SeedRNG is a simple program made for seeding the Linux kernel random number
+generator from seed files. The program takes no arguments, must be run as root,
+and always attempts to do something useful.
+
+This program is useful in light of the fact that the Linux kernel RNG cannot be
+initialized from shell scripts, and new seeds cannot be safely generated from
+boot time shell scripts either.
+
+It should be run once at init time and once at shutdown time. It can be run at
+other times without detriment as well. Whenever it is run, it writes existing
+seed files into the RNG pool, and then creates a new seed file. If the RNG is
+initialized at the time of creating a new seed file, then that new seed file is
+marked as "creditable", which means it can be used to initialize the RNG.
+Otherwise, it is marked as "non-creditable", in which case it is still used to
+seed the RNG's pool, but will not initialize the RNG.
+
+In order to ensure that entropy only ever stays the same or increases from one
+seed file to the next, old seed values are hashed together with new seed values
+when writing new seed files:
+
+```
+new_seed = new_seed[:-32] || HASH(fixed_prefix || real_time || boot_time || old_seed_len || old_seed || new_seed_len || new_seed)
+```
+
+The seed is stored in `LOCALSTATEDIR/seedrng/`, which can be adjusted at
+compile time. If the `SEEDRNG_SKIP_CREDIT` environment variable is set to `1`,
+`true`, `yes`, or `y`, then seeds never credit the RNG, even if the seed file
+is creditable.
+
+Being a single C file, `seedrng.c`, SeedRNG is meant to be copy and pasted
+verbatim into various minimal init system projects and tweaked as needed.
+**Please do not package this repo as a standalone program**: it is intended as
+utility code meant to be imported into existing projects instead.
+
+### Building & Installing
+
+```
+$ make
+$ sudo make install
+```
+
+In addition to the usual compiler environment variables (`CFLAGS`, etc), the
+following environment variable is respected during compilation:
+
+  * `LOCALSTATEDIR`        default: `/var/lib`
+
+The following environment variables are respected during installation:
+
+  * `PREFIX`               default: `/usr`
+  * `DESTDIR`              default:
+  * `SBINDIR`              default: `$(PREFIX)/sbin`
+
+### Usage
+
+```
+# seedrng
+```
+
+However, this invocation should generally come from init and shutdown scripts.
+
+### License
+
+This program is licensed under any one of the the following licenses, so that it can be incorporated into other software projects as needed:
+
+    - GPL-2.0
+    - Apache-2.0
+    - MIT
+    - BSD-1-Clause
+    - CC0-1.0

pkgs/seedrng/default.nix

@@ -0,0 +1,13 @@
+{ stdenv }:
+stdenv.mkDerivation {
+  pname = "seedrng";
+  version = "2022.04";
+
+  src = ./.;
+
+  makeFlags = [
+    "PREFIX=${placeholder "out"}"
+    "SBINDIR=${placeholder "out"}/bin"
+    "LOCALSTATEDIR=/persist"
+  ];
+}

pkgs/seedrng/seedrng.c

@@ -0,0 +1,488 @@
+// SPDX-License-Identifier: (GPL-2.0 OR Apache-2.0 OR MIT OR BSD-1-Clause OR CC0-1.0)
+/*
+ * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#include <linux/random.h>
+#include <sys/random.h>
+#include <sys/ioctl.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <unistd.h>
+#include <time.h>
+#include <errno.h>
+#include <endian.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#ifndef LOCALSTATEDIR
+#define LOCALSTATEDIR "/var/lib"
+#endif
+
+#define SEED_DIR LOCALSTATEDIR "/seedrng"
+#define CREDITABLE_SEED "seed.credit"
+#define NON_CREDITABLE_SEED "seed.no-credit"
+
+enum blake2s_lengths {
+	BLAKE2S_BLOCK_LEN = 64,
+	BLAKE2S_HASH_LEN = 32,
+	BLAKE2S_KEY_LEN = 32
+};
+
+enum seedrng_lengths {
+	MAX_SEED_LEN = 512,
+	MIN_SEED_LEN = BLAKE2S_HASH_LEN
+};
+
+struct blake2s_state {
+	uint32_t h[8];
+	uint32_t t[2];
+	uint32_t f[2];
+	uint8_t buf[BLAKE2S_BLOCK_LEN];
+	unsigned int buflen;
+	unsigned int outlen;
+};
+
+#define le32_to_cpup(a) le32toh(*(a))
+#define cpu_to_le32(a) htole32(a)
+#ifndef ARRAY_SIZE
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#endif
+#ifndef DIV_ROUND_UP
+#define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
+#endif
+
+static inline void cpu_to_le32_array(uint32_t *buf, unsigned int words)
+{
+	while (words--) {
+		*buf = cpu_to_le32(*buf);
+		++buf;
+	}
+}
+
+static inline void le32_to_cpu_array(uint32_t *buf, unsigned int words)
+{
+	while (words--) {
+		*buf = le32_to_cpup(buf);
+		++buf;
+	}
+}
+
+static inline uint32_t ror32(uint32_t word, unsigned int shift)
+{
+	return (word >> (shift & 31)) | (word << ((-shift) & 31));
+}
+
+static const uint32_t blake2s_iv[8] = {
+	0x6A09E667UL, 0xBB67AE85UL, 0x3C6EF372UL, 0xA54FF53AUL,
+	0x510E527FUL, 0x9B05688CUL, 0x1F83D9ABUL, 0x5BE0CD19UL
+};
+
+static const uint8_t blake2s_sigma[10][16] = {
+	{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 },
+	{ 14, 10, 4, 8, 9, 15, 13, 6, 1, 12, 0, 2, 11, 7, 5, 3 },
+	{ 11, 8, 12, 0, 5, 2, 15, 13, 10, 14, 3, 6, 7, 1, 9, 4 },
+	{ 7, 9, 3, 1, 13, 12, 11, 14, 2, 6, 5, 10, 4, 0, 15, 8 },
+	{ 9, 0, 5, 7, 2, 4, 10, 15, 14, 1, 11, 12, 6, 8, 3, 13 },
+	{ 2, 12, 6, 10, 0, 11, 8, 3, 4, 13, 7, 5, 15, 14, 1, 9 },
+	{ 12, 5, 1, 15, 14, 13, 4, 10, 0, 7, 6, 3, 9, 2, 8, 11 },
+	{ 13, 11, 7, 14, 12, 1, 3, 9, 5, 0, 15, 4, 8, 6, 2, 10 },
+	{ 6, 15, 14, 9, 11, 3, 0, 8, 12, 2, 13, 7, 1, 4, 10, 5 },
+	{ 10, 2, 8, 4, 7, 6, 1, 5, 15, 11, 9, 14, 3, 12, 13, 0 },
+};
+
+static void blake2s_set_lastblock(struct blake2s_state *state)
+{
+	state->f[0] = -1;
+}
+
+static void blake2s_increment_counter(struct blake2s_state *state, const uint32_t inc)
+{
+	state->t[0] += inc;
+	state->t[1] += (state->t[0] < inc);
+}
+
+static void blake2s_init_param(struct blake2s_state *state, const uint32_t param)
+{
+	int i;
+
+	memset(state, 0, sizeof(*state));
+	for (i = 0; i < 8; ++i)
+		state->h[i] = blake2s_iv[i];
+	state->h[0] ^= param;
+}
+
+static void blake2s_init(struct blake2s_state *state, const size_t outlen)
+{
+	blake2s_init_param(state, 0x01010000 | outlen);
+	state->outlen = outlen;
+}
+
+static void blake2s_compress(struct blake2s_state *state, const uint8_t *block, size_t nblocks, const uint32_t inc)
+{
+	uint32_t m[16];
+	uint32_t v[16];
+	int i;
+
+	while (nblocks > 0) {
+		blake2s_increment_counter(state, inc);
+		memcpy(m, block, BLAKE2S_BLOCK_LEN);
+		le32_to_cpu_array(m, ARRAY_SIZE(m));
+		memcpy(v, state->h, 32);
+		v[ 8] = blake2s_iv[0];
+		v[ 9] = blake2s_iv[1];
+		v[10] = blake2s_iv[2];
+		v[11] = blake2s_iv[3];
+		v[12] = blake2s_iv[4] ^ state->t[0];
+		v[13] = blake2s_iv[5] ^ state->t[1];
+		v[14] = blake2s_iv[6] ^ state->f[0];
+		v[15] = blake2s_iv[7] ^ state->f[1];
+
+#define G(r, i, a, b, c, d) do { \
+	a += b + m[blake2s_sigma[r][2 * i + 0]]; \
+	d = ror32(d ^ a, 16); \
+	c += d; \
+	b = ror32(b ^ c, 12); \
+	a += b + m[blake2s_sigma[r][2 * i + 1]]; \
+	d = ror32(d ^ a, 8); \
+	c += d; \
+	b = ror32(b ^ c, 7); \
+} while (0)
+
+#define ROUND(r) do { \
+	G(r, 0, v[0], v[ 4], v[ 8], v[12]); \
+	G(r, 1, v[1], v[ 5], v[ 9], v[13]); \
+	G(r, 2, v[2], v[ 6], v[10], v[14]); \
+	G(r, 3, v[3], v[ 7], v[11], v[15]); \
+	G(r, 4, v[0], v[ 5], v[10], v[15]); \
+	G(r, 5, v[1], v[ 6], v[11], v[12]); \
+	G(r, 6, v[2], v[ 7], v[ 8], v[13]); \
+	G(r, 7, v[3], v[ 4], v[ 9], v[14]); \
+} while (0)
+		ROUND(0);
+		ROUND(1);
+		ROUND(2);
+		ROUND(3);
+		ROUND(4);
+		ROUND(5);
+		ROUND(6);
+		ROUND(7);
+		ROUND(8);
+		ROUND(9);
+
+#undef G
+#undef ROUND
+
+		for (i = 0; i < 8; ++i)
+			state->h[i] ^= v[i] ^ v[i + 8];
+
+		block += BLAKE2S_BLOCK_LEN;
+		--nblocks;
+	}
+}
+
+static void blake2s_update(struct blake2s_state *state, const void *inp, size_t inlen)
+{
+	const size_t fill = BLAKE2S_BLOCK_LEN - state->buflen;
+	const uint8_t *in = inp;
+
+	if (!inlen)
+		return;
+	if (inlen > fill) {
+		memcpy(state->buf + state->buflen, in, fill);
+		blake2s_compress(state, state->buf, 1, BLAKE2S_BLOCK_LEN);
+		state->buflen = 0;
+		in += fill;
+		inlen -= fill;
+	}
+	if (inlen > BLAKE2S_BLOCK_LEN) {
+		const size_t nblocks = DIV_ROUND_UP(inlen, BLAKE2S_BLOCK_LEN);
+		blake2s_compress(state, in, nblocks - 1, BLAKE2S_BLOCK_LEN);
+		in += BLAKE2S_BLOCK_LEN * (nblocks - 1);
+		inlen -= BLAKE2S_BLOCK_LEN * (nblocks - 1);
+	}
+	memcpy(state->buf + state->buflen, in, inlen);
+	state->buflen += inlen;
+}
+
+static void blake2s_final(struct blake2s_state *state, uint8_t *out)
+{
+	blake2s_set_lastblock(state);
+	memset(state->buf + state->buflen, 0, BLAKE2S_BLOCK_LEN - state->buflen);
+	blake2s_compress(state, state->buf, 1, state->buflen);
+	cpu_to_le32_array(state->h, ARRAY_SIZE(state->h));
+	memcpy(out, state->h, state->outlen);
+}
+
+static ssize_t getrandom_full(void *buf, size_t count, unsigned int flags)
+{
+	ssize_t ret, total = 0;
+	uint8_t *p = buf;
+
+	do {
+		ret = getrandom(p, count, flags);
+		if (ret < 0 && errno == EINTR)
+			continue;
+		else if (ret < 0)
+			return ret;
+		total += ret;
+		p += ret;
+		count -= ret;
+	} while (count);
+	return total;
+}
+
+static ssize_t read_full(int fd, void *buf, size_t count)
+{
+	ssize_t ret, total = 0;
+	uint8_t *p = buf;
+
+	do {
+		ret = read(fd, p, count);
+		if (ret < 0 && errno == EINTR)
+			continue;
+		else if (ret < 0)
+			return ret;
+		else if (ret == 0)
+			break;
+		total += ret;
+		p += ret;
+		count -= ret;
+	} while (count);
+	return total;
+}
+
+static ssize_t write_full(int fd, const void *buf, size_t count)
+{
+	ssize_t ret, total = 0;
+	const uint8_t *p = buf;
+
+	do {
+		ret = write(fd, p, count);
+		if (ret < 0 && errno == EINTR)
+			continue;
+		else if (ret < 0)
+			return ret;
+		total += ret;
+		p += ret;
+		count -= ret;
+	} while (count);
+	return total;
+}
+
+static size_t determine_optimal_seed_len(void)
+{
+	size_t ret = 0;
+	char poolsize_str[11] = { 0 };
+	int fd = open("/proc/sys/kernel/random/poolsize", O_RDONLY);
+
+	if (fd < 0 || read_full(fd, poolsize_str, sizeof(poolsize_str) - 1) < 0) {
+		perror("Unable to determine pool size, falling back to 256 bits");
+		ret = MIN_SEED_LEN;
+	} else
+		ret = DIV_ROUND_UP(strtoul(poolsize_str, NULL, 10), 8);
+	if (fd >= 0)
+		close(fd);
+	if (ret < MIN_SEED_LEN)
+		ret = MIN_SEED_LEN;
+	else if (ret > MAX_SEED_LEN)
+		ret = MAX_SEED_LEN;
+	return ret;
+}
+
+static int read_new_seed(uint8_t *seed, size_t len, bool *is_creditable)
+{
+	ssize_t ret;
+	int urandom_fd;
+
+	*is_creditable = false;
+	ret = getrandom_full(seed, len, GRND_NONBLOCK);
+	if (ret == (ssize_t)len) {
+		*is_creditable = true;
+		return 0;
+	} else if (ret < 0 && errno == ENOSYS) {
+		struct pollfd random_fd = {
+			.fd = open("/dev/random", O_RDONLY),
+			.events = POLLIN
+		};
+		if (random_fd.fd < 0)
+			return -errno;
+		*is_creditable = poll(&random_fd, 1, 0) == 1;
+		close(random_fd.fd);
+	} else if (getrandom_full(seed, len, GRND_INSECURE) == (ssize_t)len)
+		return 0;
+	urandom_fd = open("/dev/urandom", O_RDONLY);
+	if (urandom_fd < 0)
+		return -1;
+	ret = read_full(urandom_fd, seed, len);
+	if (ret == (ssize_t)len)
+		ret = 0;
+	else
+		ret = -errno ? -errno : -EIO;
+	close(urandom_fd);
+	errno = -ret;
+	return ret ? -1 : 0;
+}
+
+static int seed_rng(uint8_t *seed, size_t len, bool credit)
+{
+	struct {
+		int entropy_count;
+		int buf_size;
+		uint8_t buffer[MAX_SEED_LEN];
+	} req = {
+		.entropy_count = credit ? len * 8 : 0,
+		.buf_size = len
+	};
+	int random_fd, ret;
+
+	if (len > sizeof(req.buffer)) {
+		errno = EFBIG;
+		return -1;
+	}
+	memcpy(req.buffer, seed, len);
+
+	random_fd = open("/dev/urandom", O_RDONLY);
+	if (random_fd < 0)
+		return -1;
+	ret = ioctl(random_fd, RNDADDENTROPY, &req);
+	if (ret)
+		ret = -errno ? -errno : -EIO;
+	close(random_fd);
+	errno = -ret;
+	return ret ? -1 : 0;
+}
+
+static int seed_from_file_if_exists(const char *filename, int dfd, bool credit, struct blake2s_state *hash)
+{
+	uint8_t seed[MAX_SEED_LEN];
+	ssize_t seed_len;
+	int fd = -1, ret = 0;
+
+	fd = openat(dfd, filename, O_RDONLY);
+	if (fd < 0 && errno == ENOENT)
+		return 0;
+	else if (fd < 0) {
+		ret = -errno;
+		perror("Unable to open seed file");
+		goto out;
+	}
+	seed_len = read_full(fd, seed, sizeof(seed));
+	if (seed_len < 0) {
+		ret = -errno;
+		perror("Unable to read seed file");
+		goto out;
+	}
+	if ((unlinkat(dfd, filename, 0) < 0 || fsync(dfd) < 0) && seed_len) {
+		ret = -errno;
+		perror("Unable to remove seed after reading, so not seeding");
+		goto out;
+	}
+	if (!seed_len)
+		goto out;
+
+	blake2s_update(hash, &seed_len, sizeof(seed_len));
+	blake2s_update(hash, seed, seed_len);
+
+	printf("Seeding %zd bits %s crediting\n", seed_len * 8, credit ? "and" : "without");
+	if (seed_rng(seed, seed_len, credit) < 0) {
+		ret = -errno;
+		perror("Unable to seed");
+	}
+
+out:
+	if (fd >= 0)
+		close(fd);
+	errno = -ret;
+	return ret ? -1 : 0;
+}
+
+static bool skip_credit(void)
+{
+	const char *skip = getenv("SEEDRNG_SKIP_CREDIT");
+	return skip && (!strcmp(skip, "1") || !strcasecmp(skip, "true") ||
+			!strcasecmp(skip, "yes") || !strcasecmp(skip, "y"));
+}
+
+int main(int argc __attribute__((unused)), char *argv[] __attribute__((unused)))
+{
+	static const char seedrng_prefix[] = "SeedRNG v1 Old+New Prefix";
+	static const char seedrng_failure[] = "SeedRNG v1 No New Seed Failure";
+	int fd = -1, dfd = -1, program_ret = 0;
+	uint8_t new_seed[MAX_SEED_LEN];
+	size_t new_seed_len;
+	bool new_seed_creditable;
+	struct timespec realtime = { 0 }, boottime = { 0 };
+	struct blake2s_state hash;
+
+	umask(0077);
+	if (getuid()) {
+		errno = EACCES;
+		perror("This program requires root");
+		return 1;
+	}
+
+	blake2s_init(&hash, BLAKE2S_HASH_LEN);
+	blake2s_update(&hash, seedrng_prefix, strlen(seedrng_prefix));
+	clock_gettime(CLOCK_REALTIME, &realtime);
+	clock_gettime(CLOCK_BOOTTIME, &boottime);
+	blake2s_update(&hash, &realtime, sizeof(realtime));
+	blake2s_update(&hash, &boottime, sizeof(boottime));
+
+	if (mkdir(SEED_DIR, 0700) < 0 && errno != EEXIST) {
+		perror("Unable to create seed directory");
+		return 1;
+	}
+
+	dfd = open(SEED_DIR, O_DIRECTORY | O_RDONLY);
+	if (dfd < 0 || flock(dfd, LOCK_EX) < 0) {
+		perror("Unable to lock seed directory");
+		program_ret = 1;
+		goto out;
+	}
+
+	if (seed_from_file_if_exists(NON_CREDITABLE_SEED, dfd, false, &hash) < 0)
+		program_ret |= 1 << 1;
+	if (seed_from_file_if_exists(CREDITABLE_SEED, dfd, !skip_credit(), &hash) < 0)
+		program_ret |= 1 << 2;
+
+	new_seed_len = determine_optimal_seed_len();
+	if (read_new_seed(new_seed, new_seed_len, &new_seed_creditable) < 0) {
+		perror("Unable to read new seed");
+		new_seed_len = BLAKE2S_HASH_LEN;
+		strncpy((char *)new_seed, seedrng_failure, new_seed_len);
+		program_ret |= 1 << 3;
+	}
+	blake2s_update(&hash, &new_seed_len, sizeof(new_seed_len));
+	blake2s_update(&hash, new_seed, new_seed_len);
+	blake2s_final(&hash, new_seed + new_seed_len - BLAKE2S_HASH_LEN);
+
+	printf("Saving %zu bits of %s seed for next boot\n", new_seed_len * 8, new_seed_creditable ? "creditable" : "non-creditable");
+	fd = openat(dfd, NON_CREDITABLE_SEED, O_WRONLY | O_CREAT | O_TRUNC, 0400);
+	if (fd < 0) {
+		perror("Unable to open seed file for writing");
+		program_ret |= 1 << 4;
+		goto out;
+	}
+	if (write_full(fd, new_seed, new_seed_len) != (ssize_t)new_seed_len || fsync(fd) < 0) {
+		perror("Unable to write seed file");
+		program_ret |= 1 << 5;
+		goto out;
+	}
+	if (new_seed_creditable && renameat(dfd, NON_CREDITABLE_SEED, dfd, CREDITABLE_SEED) < 0) {
+		perror("Unable to make new seed creditable");
+		program_ret |= 1 << 6;
+	}
+out:
+	if (fd >= 0)
+		close(fd);
+	if (dfd >= 0)
+		close(dfd);
+	return program_ret;
+}

tests/ci.nix

@@ -10,5 +10,4 @@
   tftpboot = import ./tftpboot/test.nix;
   updown = import ./updown/test.nix;
   inout = import ./inout/test.nix;
-  custom-shell = import ./custom-shell/test.nix;
 }

tests/custom-shell/check-prompt.expect

@@ -1,7 +0,0 @@
-set timeout 60
-
-spawn socat unix-connect:vm/console -
-expect {
-  "root@liminix blah blah > " { exit 0 }
-  timeout { exit 1 }
-}

tests/custom-shell/configuration.nix

@@ -1,13 +0,0 @@
-{ config, pkgs, lib, ... } :
-let
-  inherit (pkgs.liminix.networking) interface address hostapd route dnsmasq;
-  inherit (pkgs.liminix.services) oneshot longrun bundle target;
-in rec {
-  imports = [
-    ../../modules/network
-  ];
-
-  defaultProfile.prompt = "$(whoami)@$(hostname) blah blah > ";
-
-  defaultProfile.packages = with pkgs; [ ];
-}

tests/custom-shell/test.nix

@@ -1,21 +0,0 @@
-{
-  liminix
-, nixpkgs
-}:
-let img = (import liminix {
-      inherit nixpkgs;
-      device = import "${liminix}/devices/qemu/";
-      liminix-config = ./configuration.nix;
-    }).outputs.default;
-    pkgs = import nixpkgs { overlays = [(import ../../overlay.nix)]; };
-in pkgs.runCommand "check" {
-  nativeBuildInputs = with pkgs; [
-    expect socat
-  ] ;
-} ''
-. ${../test-helpers.sh}
-
-mkdir vm
-${img}/run.sh --background ./vm
-expect ${./check-prompt.expect} |tee output && mv output $out
-''