Add 'pkg/ent/' from commit '31ac2913f14c6f7631f5792ad942605fb2d9fb87'

git-subtree-dir: pkg/ent
git-subtree-mainline: 1207c204cb
git-subtree-split: 31ac2913f1

pkg/ent/.gitignore

@@ -0,0 +1,4 @@
+/*.a
+/*.o
+/out
+/test

pkg/ent/LICENSE

@@ -0,0 +1,20 @@
+Copyright 2019 Steven Dee
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be included
+in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

pkg/ent/Makefile

@@ -0,0 +1,29 @@
+CC     ?= cc
+AR     ?= ar
+PREFIX ?= ./out
+
+ifndef IMPL
+$(error IMPL must be set)
+endif
+
+################################################################################
+
+.PHONY: all test install clean
+
+all: ent.c ent.h
+	$(CC) -D$(IMPL) -O3 -Wall -Werror -pedantic -std=gnu99 -c ent.c
+	$(AR) rcs libent.a ent.o
+
+test: all
+	$(CC) -D$(IMPL) -O3 -Wall -Werror -pedantic -std=gnu99 ent.c test.c -o test
+	./test
+
+install: all
+	@mkdir -p $(PREFIX)/lib/
+	@mkdir -p $(PREFIX)/include/
+	cp libent.a $(PREFIX)/lib/
+	cp ent.h $(PREFIX)/include/
+
+clean:
+	rm -f *.o *.a test
+	rm -rf ./out

pkg/ent/README.md

@@ -0,0 +1,38 @@
+## `libent`
+
+`libent` is a cross-platform wrapper around `getentropy(2)`. It exports
+one symbol, `ent_getentropy`. If getentropy is available, then it's just
+a shim around that. Otherwise, it uses `getrandom(2)` (available since
+kernel 3.17) on Linux, or `/dev/urandom` on other \*nix.
+
+
+### Building and Testing
+
+```bash
+./configure
+make
+make test
+PREFIX=/usr/local make install
+```
+
+### Why?
+
+`getentropy` is the wave of the future. It's the correct API for
+generating small amounts of entropy to create cryptographic keys or seed
+PRNGs. It's good and reasonable and true, it's on Linux, \*BSD, and OS
+X, and it only took us fifty years of UNIX to get here.
+
+Sadly, it only just arrived, so nobody has it yet. It didn't land in
+Linux until glibc 2.25, which seems to only have made it into Debian 10.
+
+Once `getentropy` is everywhere you care about, you can just do a
+s/ent\_//g on all the call sites and discard this shim.
+
+This project began because [Urbit](https://github.com/urbit/urbit)'s
+entropy-generation function was bothering me. Then it got out of hand.
+
+
+### References
+
+* [OpenBSD getentropy](https://man.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2)
+* [djb on entropy gathering](https://blog.cr.yp.to/20140205-entropy.html)

pkg/ent/configure

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+
+log () {
+  echo "$@" >&2;
+}
+
+for impl in ENT_GETENTROPY_UNISTD \
+            ENT_GETENTROPY_SYSRANDOM \
+            ENT_GETRANDOM_SYSCALL \
+            ENT_DEV_URANDOM
+do
+    export IMPL=$impl
+
+    log "Trying IMPL=$IMPL"
+
+    if IMPL=$impl make >/dev/null 2>/dev/null
+    then sed -i 's|$(error IMPL must be set)|IMPL='"$impl"'|' Makefile
+         log "IMPL=$IMPL works"
+         exit 0
+    else log "IMPL=$IMPL failed"
+    fi
+done
+
+log "This shouldn't happen, something is broken."
+exit 1

pkg/ent/ent.c

@@ -0,0 +1,62 @@
+// Use `getentropy` from unistd.h //////////////////////////////////////////////
+
+#if defined(ENT_GETENTROPY_UNISTD)
+#include <stddef.h>
+#include <unistd.h>
+int ent_getentropy(void* buf, size_t len) {
+  return getentropy(buf, len);
+}
+
+
+// Use `getentropy` from sys/random.h //////////////////////////////////////////
+
+#elif defined(ENT_GETENTROPY_SYSRANDOM)
+#include <stddef.h>
+#include <sys/random.h>
+int ent_getentropy(void* buf, size_t len) {
+  return getentropy(buf, len);
+}
+
+
+// Use the `getrandom` syscall /////////////////////////////////////////////////
+
+#elif defined(ENT_GETRANDOM_SYSCALL)
+#include <stddef.h>
+#include <errno.h>
+#define _GNU_SOURCE
+#include <unistd.h>
+#include <sys/syscall.h>
+
+#define ENTFAIL { errno=EIO; return -1; }
+
+int ent_getentropy(void* buf, size_t len) {
+  if (len > 256) ENTFAIL
+  int r = syscall(SYS_getrandom, buf, len, 0);
+  if (r < 0) return r;
+  if (r != len) ENTFAIL
+  return 0;
+}
+
+
+// Use `/dev/urandom` //////////////////////////////////////////////////////////
+
+#elif defined(ENT_DEV_URANDOM)
+#include <stddef.h>
+#include <errno.h>
+#include <stdio.h>
+
+#define ENTFAIL { errno=EIO; return -1; }
+
+int ent_getentropy(void* buf, size_t len) {
+    if (len > 256) ENTFAIL;
+    FILE *f = fopen("/dev/urandom", "re");
+    if (!f) return -1;
+    int r = fread(buf, 1, len, f);
+    (void) fclose(f);
+    if (r != len) ENTFAIL
+    return 0;
+}
+
+#else
+#error "One of these must be set: ENT_DEV_URANDOM, ENT_GETENTROPY_UNISTD, ENT_GETENTROPY_SYSRANDOM, ENT_GETRANDOM_SYSCALL"
+#endif

pkg/ent/ent.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <stddef.h>
+
+/*
+  Fills buf with high-quality entropy.
+
+  buflen is the number of bytes, no greater than 256.
+
+  Returns 0 on success. On failure, returns -1 and sets errno to
+  indicate the error.
+*/
+int ent_getentropy(void* buf, size_t buflen);

pkg/ent/test.c

@@ -0,0 +1,20 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "ent.h"
+
+int main(void) {
+    char buf[256] = {0};
+
+    if (0 != ent_getentropy(buf, sizeof(buf))) {
+        perror("getentropy");
+        exit(1);
+    }
+
+    for (int i = 0; i < sizeof buf; i++) {
+        printf("%02hhx", buf[i]);
+    }
+
+    puts("");
+}