[LEDE-DEV] [PATCH ubox] getrandom: add helper for getrandom() syscall

[John Crispin]

its a vm that takes a few moments to get the real time hen coming out of
sleep ;)


On 09/06/2016 17:02, Etienne Champetier wrote:
> Hi,
> 
> Everything is fine except your computer clock ;)
> ubox commit:
> author    Etienne CHAMPETIER <champetier.etienne at gmail.com>
>     Thu, 9 Jun 2016 16:03:00 +0300 (13:03 +0000)
> committer    John Crispin <john at phrozen.org>
>     Wed, 8 Jun 2016 01:19:24 +0300 (00:19 +0200)
> 
> staging commit:
> author    John Crispin <john at phrozen.org>
>     Wed, 8 Jun 2016 01:22:16 +0300 (00:22 +0200)
> committer    John Crispin <john at phrozen.org>
>     Wed, 8 Jun 2016 01:56:48 +0300
> 
> Thanks
> Etienne
> 
> 2016-06-09 17:17 GMT+03:00 John Crispin <john at phrozen.org>:
>> Hi Etienne,
>>
>> pushed the patch to ubox.git and updated the ubox package inside my
>> staging tree. should the tool be installed to /usr/bin ? if not let me
>> know and i will fix the staged commit.
>>
>>         John
>>
>> On 09/06/2016 15:03, Etienne CHAMPETIER wrote:
>>> getrandom() was introduced in version 3.17 of the Linux kernel.
>>> By default getrandom() block until /dev/urandom pool has been initialized
>>> and then read from it.
>>> Read buffer is 256 bytes so getrandom() calls always succeed.
>>>
>>> First usage will be to save a seed for /dev/urandom.
>>>
>>> Signed-off-by: Etienne CHAMPETIER <champetier.etienne at gmail.com>
>>> ---
>>>  CMakeLists.txt |  5 +++++
>>>  getrandom.c    | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>  2 files changed, 63 insertions(+)
>>>  create mode 100644 getrandom.c
>>>
>>> diff --git a/CMakeLists.txt b/CMakeLists.txt
>>> index 834b5b6..73e8753 100644
>>> --- a/CMakeLists.txt
>>> +++ b/CMakeLists.txt
>>> @@ -16,6 +16,11 @@ IF(DEBUG)
>>>    ADD_DEFINITIONS(-DDEBUG -g3)
>>>  ENDIF()
>>>
>>> +ADD_EXECUTABLE(getrandom getrandom.c)
>>> +INSTALL(TARGETS getrandom
>>> +     RUNTIME DESTINATION bin
>>> +)
>>> +
>>>  ADD_EXECUTABLE(kmodloader kmodloader.c)
>>>  TARGET_LINK_LIBRARIES(kmodloader ubox)
>>>
>>> diff --git a/getrandom.c b/getrandom.c
>>> new file mode 100644
>>> index 0000000..9671202
>>> --- /dev/null
>>> +++ b/getrandom.c
>>> @@ -0,0 +1,58 @@
>>> +/*
>>> + * Copyright (C) 2016 Etienne Champetier <champetier.etienne at gmail.com>
>>> + *
>>> + * 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.
>>> + */
>>> +#define _GNU_SOURCE
>>> +#include <errno.h>
>>> +#include <linux/random.h>
>>> +#include <stdio.h>
>>> +#include <stdlib.h>
>>> +#include <string.h>
>>> +#include <sys/syscall.h>
>>> +#include <unistd.h>
>>> +
>>> +#define ERROR_EXIT(fmt, ...) do { \
>>> +        fprintf(stderr, fmt, ## __VA_ARGS__); \
>>> +        return EXIT_FAILURE; \
>>> +        } while (0)
>>> +
>>> +static int usage(char *name)
>>> +{
>>> +    fprintf(stderr, "Usage: %s <nb>\n", name);
>>> +    fprintf(stderr, " => return <nb> bytes from getrandom()\n");
>>> +    return EXIT_FAILURE;
>>> +}
>>> +
>>> +int main(int argc, char *argv[])
>>> +{
>>> +    if (argc != 2)
>>> +        return usage(argv[0]);
>>> +
>>> +    if (isatty(STDOUT_FILENO))
>>> +        ERROR_EXIT("Not outputting random to a tty\n");
>>> +
>>> +    int nbtot = atoi(argv[1]);
>>> +    if (nbtot < 1)
>>> +        ERROR_EXIT("Invalid <nb> param (must be > 0)\n");
>>> +
>>> +    char buf[256];
>>> +    int len = sizeof(buf);
>>> +    while (nbtot > 0) {
>>> +        if (nbtot <= sizeof(buf))
>>> +            len = nbtot;
>>> +        if (syscall(SYS_getrandom, buf, len, 0) == -1)
>>> +            ERROR_EXIT("getrandom() failed: %s\n", strerror(errno));
>>> +        if (write(STDOUT_FILENO, buf, len) != len)
>>> +            ERROR_EXIT("write() failed: %s\n", strerror(errno));
>>> +        nbtot -= sizeof(buf);
>>> +    }
>>> +}
>>>
>>
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