Use getrandom() in Linux instead of /dev/urandom

[oittaa]

Using getrandom() instead of opening /dev/urandom is the preferred way to get random bytes in modern Linux systems.

Something like the following could be used in src/random/random.c:

/********************************************************************************************
* Hardware-based random number generation function
*
* It uses /dev/urandom in Linux and CNG's BCryptGenRandom function in Windows
*********************************************************************************************/ 

#include "random.h"
#include <stdlib.h>
#if defined(__WINDOWS__)
    #include <windows.h>
    #include <bcrypt.h>
#elif defined(__LINUX__)
    #include <unistd.h>
    #include <fcntl.h>
    #include <sys/random.h>
    #include <errno.h>
    static int lock = -1;
    static int getrandom_works = 1;
#endif

#define passed 0 
#define failed 1


static __inline void delay(unsigned int count)
{
    while (count--) {}
}


int randombytes(unsigned char* random_array, unsigned long long nbytes)
{ // Generation of "nbytes" of random values
    
#if defined(__WINDOWS__)   
    if (!BCRYPT_SUCCESS(BCryptGenRandom(NULL, random_array, (unsigned long)nbytes, BCRYPT_USE_SYSTEM_PREFERRED_RNG))) {
        return failed;
    }

#elif defined(__LINUX__)
    int r, n = (int)nbytes, count = 0;
    
    if (getrandom_works == 1) {
        errno = 0;
        while (n > 0) {
            r = getrandom(random_array+count, n, 0);
            if (r < 0) {
                if (errno == EINTR) {
                    /* retry getrandom() if it was interrupted by a signal */
                    continue;
                }
                getrandom_works = 0;
                break;
            }
            count += r;
            n -= r;
        }
        if (n == 0) {
            return passed;
        }
    }

    if (lock == -1) {
        do {
            lock = open("/dev/urandom", O_RDONLY);
            if (lock == -1) {
                delay(0xFFFFF);
            }
        } while (lock == -1);
    }

    while (n > 0) {
        do {
            r = read(lock, random_array+count, n);
            if (r == -1) {
                delay(0xFFFF);
            }
        } while (r == -1);
        count += r;
        n -= r;
    }
#endif

    return passed;
}

[rdp]

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