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/* fhandler_random.cc: code to access /dev/random and /dev/urandom
This file is part of Cygwin.
This software is a copyrighted work licensed under the terms of the
Cygwin license. Please consult the file "CYGWIN_LICENSE" for
details. */
#include "winsup.h"
#include <unistd.h>
#include <sys/param.h>
#include "cygerrno.h"
#include "path.h"
#include "fhandler.h"
#include "sync.h"
#include "dtable.h"
#include "cygheap.h"
#include "child_info.h"
#define RANDOM 8
#define URANDOM 9
/* The system PRNG is reseeded after reading 128K bytes. */
#define RESEED_INTERVAL (128 * 1024)
#define PSEUDO_MULTIPLIER (6364136223846793005LL)
#define PSEUDO_SHIFTVAL (21)
int
fhandler_dev_random::pseudo_write (const void *ptr, size_t len)
{
/* Use buffer to mess up the pseudo random number generator. */
for (size_t i = 0; i < len; ++i)
pseudo = (pseudo + ((unsigned char *)ptr)[i]) * PSEUDO_MULTIPLIER + 1;
return len;
}
ssize_t __stdcall
fhandler_dev_random::write (const void *ptr, size_t len)
{
if (!len)
return 0;
if (!ptr)
{
set_errno (EINVAL);
return -1;
}
/* Limit len to a value <= 4096 since we don't want to overact.
Copy to local buffer because CryptGenRandom violates const. */
size_t limited_len = MIN (len, 4096);
unsigned char buf[limited_len];
memcpy (buf, ptr, limited_len);
/* Mess up system entropy source. Return error if device is /dev/random. */
if (getentropy (buf, limited_len) && dev () == FH_RANDOM)
return -1;
/* Mess up the pseudo random number generator. */
pseudo_write (buf, limited_len);
return len;
}
int
fhandler_dev_random::pseudo_read (void *ptr, size_t len)
{
/* Use pseudo random number generator as fallback entropy source.
This multiplier was obtained from Knuth, D.E., "The Art of
Computer Programming," Vol 2, Seminumerical Algorithms, Third
Edition, Addison-Wesley, 1998, p. 106 (line 26) & p. 108 */
for (size_t i = 0; i < len; ++i)
{
pseudo = pseudo * PSEUDO_MULTIPLIER + 1;
((unsigned char *)ptr)[i] = (pseudo >> PSEUDO_SHIFTVAL) & UCHAR_MAX;
}
return len;
}
void __reg3
fhandler_dev_random::read (void *ptr, size_t& len)
{
if (!len)
return;
if (!ptr)
{
set_errno (EINVAL);
len = (size_t) -1;
return;
}
/* /dev/random has to provide high quality random numbers. Therefore we
re-seed the system PRNG for each block of 512 bytes. This results in
sufficiently random sequences, comparable to the Linux /dev/random. */
if (dev () == FH_RANDOM)
{
void *dummy = malloc (RESEED_INTERVAL);
if (!dummy)
{
__seterrno ();
len = (size_t) -1;
return;
}
for (size_t offset = 0; offset < len; offset += 512)
{
if (getentropy (dummy, RESEED_INTERVAL) ||
getentropy ((PBYTE) ptr + offset, len - offset))
{
len = (size_t) -1;
break;
}
}
free (dummy);
}
/* If device is /dev/urandom, just use system RNG as is, with our own
PRNG as fallback. */
else if (getentropy (ptr, len))
len = pseudo_read (ptr, len);
}
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