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/* fhandler_random.cc: code to access /dev/random and /dev/urandom
Copyright 2000, 2001, 2002, 2003, 2004, 2005, 2007, 2009, 2011 Red Hat, Inc.
Written by Corinna Vinschen (vinschen@cygnus.com)
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 "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
#define PSEUDO_MULTIPLIER (6364136223846793005LL)
#define PSEUDO_SHIFTVAL (21)
fhandler_dev_random::fhandler_dev_random ()
: fhandler_base (), crypt_prov ((HCRYPTPROV) NULL)
{
}
int
fhandler_dev_random::open (int flags, mode_t)
{
set_flags ((flags & ~O_TEXT) | O_BINARY);
nohandle (true);
set_open_status ();
dummy_offset = 0;
return 1;
}
bool
fhandler_dev_random::crypt_gen_random (void *ptr, size_t len)
{
if (!crypt_prov
&& !CryptAcquireContextW (&crypt_prov, NULL, MS_DEF_PROV_W, PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET)
&& !CryptAcquireContextW (&crypt_prov, NULL, MS_DEF_PROV_W, PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET
| CRYPT_NEWKEYSET))
{
debug_printf ("%E = CryptAquireContext()");
return false;
}
if (!CryptGenRandom (crypt_prov, len, (BYTE *)ptr))
{
debug_printf ("%E = CryptGenRandom()");
return false;
}
return true;
}
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 <= 512 since we don't want to overact.
Copy to local buffer because CryptGenRandom violates const. */
unsigned char buf[512];
size_t limited_len = len <= 512 ? len : 512;
memcpy (buf, ptr, limited_len);
/* Mess up system entropy source. Return error if device is /dev/random. */
if (!crypt_gen_random (buf, limited_len) && dev () == FH_RANDOM)
{
__seterrno ();
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;
}
if (crypt_gen_random (ptr, len))
return;
/* If device is /dev/urandom, use pseudo number generator as fallback.
Don't do this for /dev/random since it's intended for uses that need
very high quality randomness. */
if (dev () == FH_URANDOM)
{
len = pseudo_read (ptr, len);
return;
}
__seterrno ();
len = (size_t) -1;
}
off_t
fhandler_dev_random::lseek (off_t off, int whence)
{
/* As on Linux, fake being able to set an offset. The fact that neither
reading nor writing changes the dummy offset is also the same as on
Linux (tested with kernel 2.6.23). */
off_t new_off;
switch (whence)
{
case SEEK_SET:
new_off = off;
break;
case SEEK_CUR:
new_off = dummy_offset + off;
break;
default:
set_errno (EINVAL);
return (off_t) -1;
}
if (new_off < 0)
{
set_errno (EINVAL);
return (off_t) -1;
}
return dummy_offset = new_off;
}
int
fhandler_dev_random::close ()
{
if (!have_execed && crypt_prov)
while (!CryptReleaseContext (crypt_prov, 0)
&& GetLastError () == ERROR_BUSY)
Sleep (10);
return 0;
}
int
fhandler_dev_random::dup (fhandler_base *child, int)
{
fhandler_dev_random *fhr = (fhandler_dev_random *) child;
fhr->crypt_prov = (HCRYPTPROV)NULL;
return 0;
}
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