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util: rework timestamp fuzzing

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Use UTI_GetRandomBytes() instead of random() to generate random bits
below precision. Save the result in NTP_int64 in the network order and
allow precision in the full range from -32 to 32. With precision 32
the fuzzing now makes the timestamp completely random and can be used to
hide the time.
This commit is contained in:
Miroslav Lichvar
2015-11-10 17:26:59 +01:00
parent 6199a89170
commit 116c697282
3 changed files with 37 additions and 27 deletions
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41
util.c
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@@ -566,16 +566,21 @@ UTI_AdjustTimeval(struct timeval *old_tv, struct timeval *when, struct timeval *
/* ================================================== */
uint32_t
UTI_GetNTPTsFuzz(int precision)
void
UTI_GetInt64Fuzz(NTP_int64 *ts, int precision)
{
uint32_t fuzz;
int fuzz_bits;
fuzz_bits = 32 - 1 + precision;
fuzz = random() % (1 << fuzz_bits);
int start, bits;
return fuzz;
assert(precision >= -32 && precision <= 32);
start = sizeof (*ts) - (precision + 32 + 7) / 8;
ts->hi = ts->lo = 0;
UTI_GetRandomBytes((unsigned char *)ts + start, sizeof (*ts) - start);
bits = (precision + 32) % 8;
if (bits)
((unsigned char *)ts)[start] %= 1U << bits;
}
/* ================================================== */
@@ -608,9 +613,9 @@ UTI_DoubleToInt32(double x)
void
UTI_TimevalToInt64(struct timeval *src,
NTP_int64 *dest, uint32_t fuzz)
NTP_int64 *dest, NTP_int64 *fuzz)
{
uint32_t lo, sec, usec;
uint32_t hi, lo, sec, usec;
sec = (uint32_t)src->tv_sec;
usec = (uint32_t)src->tv_usec;
@@ -618,18 +623,22 @@ UTI_TimevalToInt64(struct timeval *src,
/* Recognize zero as a special case - it always signifies
an 'unknown' value */
if (!usec && !sec) {
dest->hi = dest->lo = 0;
hi = lo = 0;
} else {
dest->hi = htonl(sec + JAN_1970);
hi = htonl(sec + JAN_1970);
/* This formula gives an error of about 0.1us worst case */
lo = 4295 * usec - (usec>>5) - (usec>>9);
lo = htonl(4295 * usec - (usec >> 5) - (usec >> 9));
/* Add the fuzz */
lo ^= fuzz;
dest->lo = htonl(lo);
if (fuzz) {
hi ^= fuzz->hi;
lo ^= fuzz->lo;
}
}
dest->hi = hi;
dest->lo = lo;
}
/* ================================================== */