120 lines
3.0 KiB
C++
120 lines
3.0 KiB
C++
/* 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);
|
|
}
|