Initial commit

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

5 files changed, 1086 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
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--- /dev/null
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+seedrng
+*.swp
diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000..35e02b0
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,571 @@
+This project is licensed under any one of:
+
+- GPL v2
+- MIT
+- Apache 2.0
+
+Choose which one works best for you. They are reproduced below.
+
+-------------------------------------------------------------------------------
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The licenses for most software are designed to take away your
+freedom to share and change it.  By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.)  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+this service if you wish), that you receive source code or can get it
+if you want it, that you can change the software or use pieces of it
+in new free programs; and that you know you can do these things.
+
+  To protect your rights, we need to make restrictions that forbid
+anyone to deny you these rights or to ask you to surrender the rights.
+These restrictions translate to certain responsibilities for you if you
+distribute copies of the software, or if you modify it.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must give the recipients all the rights that
+you have.  You must make sure that they, too, receive or can get the
+source code.  And you must show them these terms so they know their
+rights.
+
+  We protect your rights with two steps: (1) copyright the software, and
+(2) offer you this license which gives you legal permission to copy,
+distribute and/or modify the software.
+
+  Also, for each author's protection and ours, we want to make certain
+that everyone understands that there is no warranty for this free
+software.  If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
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+
+  Finally, any free program is threatened constantly by software
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+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+                    GNU GENERAL PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+  0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License.  The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language.  (Hereinafter, translation is included without limitation in
+the term "modification".)  Each licensee is addressed as "you".
+
+Activities other than copying, distribution and modification are not
+covered by this License; they are outside its scope.  The act of
+running the Program is not restricted, and the output from the Program
+is covered only if its contents constitute a work based on the
+Program (independent of having been made by running the Program).
+Whether that is true depends on what the Program does.
+
+  1. You may copy and distribute verbatim copies of the Program's
+source code as you receive it, in any medium, provided that you
+conspicuously and appropriately publish on each copy an appropriate
+copyright notice and disclaimer of warranty; keep intact all the
+notices that refer to this License and to the absence of any warranty;
+and give any other recipients of the Program a copy of this License
+along with the Program.
+
+You may charge a fee for the physical act of transferring a copy, and
+you may at your option offer warranty protection in exchange for a fee.
+
+  2. You may modify your copy or copies of the Program or any portion
+of it, thus forming a work based on the Program, and copy and
+distribute such modifications or work under the terms of Section 1
+above, provided that you also meet all of these conditions:
+
+    a) You must cause the modified files to carry prominent notices
+    stating that you changed the files and the date of any change.
+
+    b) You must cause any work that you distribute or publish, that in
+    whole or in part contains or is derived from the Program or any
+    part thereof, to be licensed as a whole at no charge to all third
+    parties under the terms of this License.
+
+    c) If the modified program normally reads commands interactively
+    when run, you must cause it, when started running for such
+    interactive use in the most ordinary way, to print or display an
+    announcement including an appropriate copyright notice and a
+    notice that there is no warranty (or else, saying that you provide
+    a warranty) and that users may redistribute the program under
+    these conditions, and telling the user how to view a copy of this
+    License.  (Exception: if the Program itself is interactive but
+    does not normally print such an announcement, your work based on
+    the Program is not required to print an announcement.)
+
+These requirements apply to the modified work as a whole.  If
+identifiable sections of that work are not derived from the Program,
+and can be reasonably considered independent and separate works in
+themselves, then this License, and its terms, do not apply to those
+sections when you distribute them as separate works.  But when you
+distribute the same sections as part of a whole which is a work based
+on the Program, the distribution of the whole must be on the terms of
+this License, whose permissions for other licensees extend to the
+entire whole, and thus to each and every part regardless of who wrote it.
+
+Thus, it is not the intent of this section to claim rights or contest
+your rights to work written entirely by you; rather, the intent is to
+exercise the right to control the distribution of derivative or
+collective works based on the Program.
+
+In addition, mere aggregation of another work not based on the Program
+with the Program (or with a work based on the Program) on a volume of
+a storage or distribution medium does not bring the other work under
+the scope of this License.
+
+  3. You may copy and distribute the Program (or a work based on it,
+under Section 2) in object code or executable form under the terms of
+Sections 1 and 2 above provided that you also do one of the following:
+
+    a) Accompany it with the complete corresponding machine-readable
+    source code, which must be distributed under the terms of Sections
+    1 and 2 above on a medium customarily used for software interchange; or,
+
+    b) Accompany it with a written offer, valid for at least three
+    years, to give any third party, for a charge no more than your
+    cost of physically performing source distribution, a complete
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+    c) Accompany it with the information you received as to the offer
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+    allowed only for noncommercial distribution and only if you
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+The source code for a work means the preferred form of the work for
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+
+  4. You may not copy, modify, sublicense, or distribute the Program
+except as expressly provided under this License.  Any attempt
+otherwise to copy, modify, sublicense or distribute the Program is
+void, and will automatically terminate your rights under this License.
+However, parties who have received copies, or rights, from you under
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+parties remain in full compliance.
+
+  5. You are not required to accept this License, since you have not
+signed it.  However, nothing else grants you permission to modify or
+distribute the Program or its derivative works.  These actions are
+prohibited by law if you do not accept this License.  Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+  6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions.  You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
+this License.
+
+  7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
+conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
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+distribute so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you
+may not distribute the Program at all.  For example, if a patent
+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
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+
+It is not the purpose of this section to induce you to infringe any
+patents or other property right claims or to contest validity of any
+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices.  Many people have made
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+to distribute software through any other system and a licensee cannot
+impose that choice.
+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+  8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded.  In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+  9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number.  If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation.  If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+  10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission.  For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this.  Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+                            NO WARRANTY
+
+  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
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+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    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 Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  <signature of Ty Coon>, 1 April 1989
+  Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
+-------------------------------------------------------------------------------
+MIT License
+
+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,
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+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.
+-------------------------------------------------------------------------------
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
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+
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+      You may add Your own copyright statement to Your modifications and
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+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
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+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
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+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
+      incidental, or consequential damages of any character arising as a
+      result of this License or out of the use or inability to use the
+      Work (including but not limited to damages for loss of goodwill,
+      work stoppage, computer failure or malfunction, or any and all
+      other commercial damages or losses), even if such Contributor
+      has been advised of the possibility of such damages.
+
+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+-------------------------------------------------------------------------------
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..ef3e0e2
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,19 @@
+PREFIX ?= /usr
+DESTDIR ?=
+SBINDIR ?= $(PREFIX)/sbin
+LOCALSTATEDIR ?= /var/lib
+RUNSTATEDIR ?= /var/run
+CFLAGS ?= -O2 -pipe
+
+CFLAGS += -std=gnu99 -Wall -Wextra
+CFLAGS += -DLOCALSTATEDIR="\"$(LOCALSTATEDIR)\"" -DRUNSTATEDIR="\"$(RUNSTATEDIR)\""
+
+seedrng: seedrng.c
+
+install: seedrng
+	install -v -d "$(DESTDIR)$(SBINDIR)" && install -v -m 0755 seedrng "$(DESTDIR)$(SBINDIR)/seedrng"
+
+clean:
+	rm -f seedrng
+
+.PHONY: clean
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..f95d75c
--- /dev/null
+++ b/README.md
@@ -0,0 +1,63 @@
+## SeedRNG &mdash; `seedrng(8)`
+##### by [Jason A. Donenfeld](mailto:Jason@zx2c4.com)
+
+SeedRNG is a simple program made for seeding the Linux kernel random number
+generator from seed files. The program takes no arguments, must be run as root,
+and always attempts to do something useful.
+
+Being a single C file, `seedrng.c`, SeedRNG is meant to be copy and pasted
+verbatim into various minimal init system projects and tweaked as needed.
+
+This program is useful in light of the fact that the Linux kernel RNG cannot be
+initialized from shell scripts, and new seeds cannot be safely generated from
+boot time shell scripts either.
+
+It should be run once at init time and once at shutdown time. It can be run at
+other times without detriment as well. Whenever it is run, it writes existing
+seed files into the RNG pool, and then creates a new seed file. If the RNG is
+initialized at the time of creating a new seed file, then that new seed file is
+marked as "creditable", which means it can be used to initialize the RNG.
+Otherwise, it is marked as "non-creditable", in which case it is still used to
+seed the RNG's pool, but will not initialize the RNG.
+
+In order to ensure that entropy only ever stays the same or increases from one
+seed file to the next, old seed values are hashed together with new seed values
+when writing new seed files:
+
+```
+new_seed = new_seed[:-32] || HASH(fixed_prefix || real_time || boot_time || old_seed_len || old_seed || new_seed_len || new_seed)
+```
+
+The seed is stored in `LOCALSTATEDIR/seedrng/`, which can be adjusted at compile time.
+
+### Building &amp; Installing
+
+```
+$ 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`
+  * `RUNSTATEDIR`          default: `/var/run`
+
+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 GPL v2, MIT, or Apache 2.0, so
+that it can be incorporated into other software projects as needed.
diff --git a/seedrng.c b/seedrng.c
new file mode 100644
index 0000000..ff13b51
--- /dev/null
+++ b/seedrng.c
@@ -0,0 +1,431 @@
+// SPDX-License-Identifier: (GPL-2.0 OR MIT OR Apache-2.0)
+/*
+ * 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
+#ifndef RUNSTATEDIR
+#define RUNSTATEDIR "/var/run"
+#endif
+
+#define SEED_DIR LOCALSTATEDIR "/seedrng"
+#define CREDITABLE_SEED SEED_DIR "/seed.credit"
+#define NON_CREDITABLE_SEED SEED_DIR "/seed.no-credit"
+#define LOCK_FILE RUNSTATEDIR "/seedrng.lock"
+
+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 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(fd, poolsize_str, sizeof(poolsize_str) - 1) < 0) {
+		fprintf(stderr, "WARNING: Unable to determine pool size, falling back to %u bits: %s\n", MIN_SEED_LEN * 8, strerror(errno));
+		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(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(seed, len, GRND_INSECURE) == (ssize_t)len)
+		return 0;
+	urandom_fd = open("/dev/urandom", O_RDONLY);
+	if (urandom_fd < 0)
+		return -errno;
+	ret = read(urandom_fd, seed, len);
+	if (ret == (ssize_t)len)
+		ret = 0;
+	else
+		ret = -errno ?: -EIO;
+	close(urandom_fd);
+	return ret;
+}
+
+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))
+		return -EFBIG;
+	memcpy(req.buffer, seed, len);
+
+	random_fd = open("/dev/random", O_RDWR);
+	if (random_fd < 0)
+		return -errno;
+	ret = ioctl(random_fd, RNDADDENTROPY, &req);
+	if (ret)
+		ret = -errno ?: -EIO;
+	close(random_fd);
+	return ret;
+}
+
+static int seed_from_file_if_exists(const char *filename, bool credit, struct blake2s_state *hash)
+{
+	uint8_t seed[MAX_SEED_LEN];
+	ssize_t seed_len;
+	int fd, dfd, ret = 0;
+
+	fd = open(filename, O_RDONLY);
+	if (fd < 0 && errno == ENOENT)
+		return 0;
+	else if (fd < 0) {
+		ret = -errno;
+		fprintf(stderr, "ERROR: Unable to open seed file: %s\n", strerror(errno));
+		return ret;
+	}
+	dfd = open(SEED_DIR, O_DIRECTORY | O_RDONLY);
+	if (dfd < 0) {
+		ret = -errno;
+		close(fd);
+		fprintf(stderr, "ERROR: Unable to open seed directory: %s\n", strerror(errno));
+		return ret;
+	}
+	seed_len = read(fd, seed, sizeof(seed));
+	if (seed_len < 0) {
+		ret = -errno;
+		fprintf(stderr, "ERROR: Unable to read seed file: %s\n", strerror(errno));
+	}
+	close(fd);
+	if (ret) {
+		close(dfd);
+		return ret;
+	}
+	if ((unlink(filename) < 0 || fsync(dfd) < 0) && seed_len) {
+		ret = -errno;
+		fprintf(stderr, "ERROR: Unable to remove seed after reading, so not seeding: %s\n", strerror(errno));
+	}
+	close(dfd);
+	if (ret)
+		return ret;
+	if (!seed_len)
+		return 0;
+
+	blake2s_update(hash, &seed_len, sizeof(seed_len));
+	blake2s_update(hash, seed, seed_len);
+
+	fprintf(stderr, "Seeding %zd bits %s crediting\n", seed_len * 8, credit ? "and" : "without");
+	ret = seed_rng(seed, seed_len, credit);
+	if (ret < 0)
+		fprintf(stderr, "ERROR: Unable to seed: %s\n", strerror(-ret));
+	return ret;
+}
+
+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 ret, fd, lock, 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()) {
+		fprintf(stderr, "ERROR: This program requires root\n");
+		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) {
+		fprintf(stderr, "ERROR: Unable to create \"%s\" directory: %s\n", SEED_DIR, strerror(errno));
+		return 1;
+	}
+
+	lock = open(LOCK_FILE, O_WRONLY | O_CREAT, 0000);
+	if (lock < 0 || flock(lock, LOCK_EX) < 0) {
+		fprintf(stderr, "ERROR: Unable to open lock file: %s\n", strerror(errno));
+		return 1;
+	}
+
+	ret = seed_from_file_if_exists(NON_CREDITABLE_SEED, false, &hash);
+	if (ret < 0)
+		program_ret |= 1 << 1;
+	ret = seed_from_file_if_exists(CREDITABLE_SEED, true, &hash);
+	if (ret < 0)
+		program_ret |= 1 << 2;
+
+	new_seed_len = determine_optimal_seed_len();
+	ret = read_new_seed(new_seed, new_seed_len, &new_seed_creditable);
+	if (ret < 0) {
+		fprintf(stderr, "ERROR: Unable to read new seed: %s\n", strerror(-ret));
+		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);
+
+	fprintf(stderr, "Saving %zu bits of %s seed for next boot\n", new_seed_len * 8, new_seed_creditable ? "creditable" : "non-creditable");
+	fd = open(NON_CREDITABLE_SEED, O_WRONLY | O_CREAT | O_TRUNC, 0400);
+	if (fd < 0) {
+		fprintf(stderr, "ERROR: Unable to open seed file for writing: %s\n", strerror(errno));
+		program_ret |= 1 << 4;
+		goto out;
+	}
+	if (write(fd, new_seed, new_seed_len) != (ssize_t)new_seed_len || fsync(fd) < 0) {
+		fprintf(stderr, "ERROR: Unable to write seed file: %s\n", strerror(errno));
+		program_ret |= 1 << 5;
+		goto out;
+	}
+	if (new_seed_creditable && rename(NON_CREDITABLE_SEED, CREDITABLE_SEED) < 0) {
+		fprintf(stderr, "WARNING: Unable to make new seed creditable: %s\n", strerror(errno));
+		program_ret |= 1 << 6;
+	}
+out:
+	close(fd);
+	close(lock);
+	return program_ret;
+}