139 lines
3.3 KiB
C++
139 lines
3.3 KiB
C++
/* fhandler_random.cc: code to access /dev/random and /dev/urandom
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This file is part of Cygwin.
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This software is a copyrighted work licensed under the terms of the
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Cygwin license. Please consult the file "CYGWIN_LICENSE" for
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details. */
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#include "winsup.h"
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#include <ntsecapi.h>
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#include <unistd.h>
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#include <sys/param.h>
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#include "cygerrno.h"
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#include "path.h"
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#include "fhandler.h"
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#include "sync.h"
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#include "dtable.h"
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#include "cygheap.h"
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#include "child_info.h"
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#define RANDOM 8
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#define URANDOM 9
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/* The system PRNG is reseeded after reading 128K bytes. */
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#define RESEED_INTERVAL (128 * 1024)
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#define PSEUDO_MULTIPLIER (6364136223846793005LL)
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#define PSEUDO_SHIFTVAL (21)
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int
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fhandler_dev_random::pseudo_write (const void *ptr, size_t len)
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{
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/* Use buffer to mess up the pseudo random number generator. */
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for (size_t i = 0; i < len; ++i)
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pseudo = (pseudo + ((unsigned char *)ptr)[i]) * PSEUDO_MULTIPLIER + 1;
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return len;
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}
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ssize_t __stdcall
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fhandler_dev_random::write (const void *ptr, size_t len)
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{
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if (!len)
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return 0;
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if (!ptr)
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{
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set_errno (EINVAL);
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return -1;
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}
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/* Limit len to a value <= 4096 since we don't want to overact.
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Copy to local buffer because RtlGenRandom violates const. */
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size_t limited_len = MIN (len, 4096);
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unsigned char buf[limited_len];
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/* Mess up system entropy source. Return error if device is /dev/random. */
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__try
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{
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memcpy (buf, ptr, limited_len);
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if (!RtlGenRandom (buf, limited_len) && dev () == FH_RANDOM)
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return -1;
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/* Mess up the pseudo random number generator. */
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pseudo_write (buf, limited_len);
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}
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__except (EFAULT)
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{
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len = -1;
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}
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__endtry
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/* Note that we return len, not limited_len. No reason to confuse the
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caller... */
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return len;
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}
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int
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fhandler_dev_random::pseudo_read (void *ptr, size_t len)
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{
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/* Use pseudo random number generator as fallback entropy source.
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This multiplier was obtained from Knuth, D.E., "The Art of
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Computer Programming," Vol 2, Seminumerical Algorithms, Third
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Edition, Addison-Wesley, 1998, p. 106 (line 26) & p. 108 */
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for (size_t i = 0; i < len; ++i)
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{
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pseudo = pseudo * PSEUDO_MULTIPLIER + 1;
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((unsigned char *)ptr)[i] = (pseudo >> PSEUDO_SHIFTVAL) & UCHAR_MAX;
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}
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return len;
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}
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void __reg3
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fhandler_dev_random::read (void *ptr, size_t& len)
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{
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if (!len)
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return;
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if (!ptr)
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{
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set_errno (EINVAL);
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len = (size_t) -1;
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return;
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}
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__try
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{
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/* /dev/random has to provide high quality random numbers. Therefore we
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re-seed the system PRNG for each block of 512 bytes. This results in
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sufficiently random sequences, comparable to the Linux /dev/random. */
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if (dev () == FH_RANDOM)
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{
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void *dummy = malloc (RESEED_INTERVAL);
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if (!dummy)
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{
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__seterrno ();
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len = (size_t) -1;
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return;
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}
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for (size_t offset = 0; offset < len; offset += 512)
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{
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if (!RtlGenRandom (dummy, RESEED_INTERVAL) ||
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!RtlGenRandom ((PBYTE) ptr + offset, len - offset))
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{
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len = (size_t) -1;
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break;
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}
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}
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free (dummy);
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}
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/* If device is /dev/urandom, just use system RNG as is, with our own
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PRNG as fallback. */
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else if (!RtlGenRandom (ptr, len))
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len = pseudo_read (ptr, len);
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}
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__except (EFAULT)
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{
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len = (size_t) -1;
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}
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__endtry
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}
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