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cutils: Improve qemu_strtosz handling of fractions

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We have several limitations and bugs worth fixing; they are
inter-related enough that it is not worth splitting this patch into
smaller pieces:

* ".5k" should work to specify 512, just as "0.5k" does
* "1.9999k" and "1." + "9"*50 + "k" should both produce the same
  result of 2048 after rounding
* "1." + "0"*350 + "1B" should not be treated the same as "1.0B";
  underflow in the fraction should not be lost
* "7.99e99" and "7.99e999" look similar, but our code was doing a
  read-out-of-bounds on the latter because it was not expecting ERANGE
  due to overflow. While we document that scientific notation is not
  supported, and the previous patch actually fixed
  qemu_strtod_finite() to no longer return ERANGE overflows, it is
  easier to pre-filter than to try and determine after the fact if
  strtod() consumed more than we wanted.  Note that this is a
  low-level semantic change (when endptr is not NULL, we can now
  successfully parse with a scale of 'E' and then report trailing
  junk, instead of failing outright with EINVAL); but an earlier
  commit already argued that this is not a high-level semantic change
  since the only caller passing in a non-NULL endptr also checks that
  the tail is whitespace-only.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1629
Fixes: cf923b78 ("utils: Improve qemu_strtosz() to have 64 bits of precision", 6.0.0)
Fixes: 7625a1ed ("utils: Use fixed-point arithmetic in qemu_strtosz", 6.0.0)
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-Id: <20230522190441.64278-20-eblake@redhat.com>
[eblake: tweak function comment for accuracy]
This commit is contained in:
Eric Blake 2023-05-22 14:04:41 -05:00
parent c25b168344
commit 42cc08d13a
2 changed files with 88 additions and 54 deletions
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92
util/cutils.c
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@ -194,15 +194,19 @@ static int64_t suffix_mul(char suffix, int64_t unit)
* - 12345 - decimal, scale determined by @default_suffix and @unit
* - 12345{bBkKmMgGtTpPeE} - decimal, scale determined by suffix and @unit
* - 12345.678{kKmMgGtTpPeE} - decimal, scale determined by suffix, and
* fractional portion is truncated to byte
* fractional portion is truncated to byte, either side of . may be empty
* - 0x7fEE - hexadecimal, unit determined by @default_suffix
*
* The following are intentionally not supported
* - hex with scaling suffix, such as 0x20M
* - octal, such as 08
* - fractional hex, such as 0x1.8
* - negative values, including -0
* - floating point exponents, such as 1e3
* - hex with scaling suffix, such as 0x20M or 0x1p3 (both fail with
* -EINVAL), while 0x1b is 27 (not 1 with byte scale)
* - octal, such as 08 (parsed as decimal instead)
* - binary, such as 0b1000 (parsed as 0b with trailing garbage "1000")
* - fractional hex, such as 0x1.8 (parsed as 0 with trailing garbage "x1.8")
* - negative values, including -0 (fail with -ERANGE)
* - floating point exponents, such as 1e3 (parsed as 1e with trailing
* garbage "3") or 0x1p3 (rejected as hex with scaling suffix)
* - non-finite values, such as inf or NaN (fail with -EINVAL)
*
* The end pointer will be returned in *end, if not NULL. If there is
* no fraction, the input can be decimal or hexadecimal; if there is a
@ -221,17 +225,17 @@ static int do_strtosz(const char *nptr, const char **end,
uint64_t *result)
{
int retval;
const char *endptr, *f;
const char *endptr;
unsigned char c;
uint64_t val, valf = 0;
uint64_t val = 0, valf = 0;
int64_t mul;
/* Parse integral portion as decimal. */
retval = parse_uint(nptr, &endptr, 10, &val);
if (retval) {
if (retval == -ERANGE || !nptr) {
goto out;
}
if (val == 0 && (*endptr == 'x' || *endptr == 'X')) {
if (retval == 0 && val == 0 && (*endptr == 'x' || *endptr == 'X')) {
/* Input looks like hex; reparse, and insist on no fraction or suffix. */
retval = qemu_strtou64(nptr, &endptr, 16, &val);
if (retval) {
@ -242,26 +246,68 @@ static int do_strtosz(const char *nptr, const char **end,
retval = -EINVAL;
goto out;
}
} else if (*endptr == '.') {
} else if (*endptr == '.' || (endptr == nptr && strchr(nptr, '.'))) {
/*
* Input looks like a fraction. Make sure even 1.k works
* without fractional digits. If we see an exponent, treat
* the entire input as invalid instead.
* without fractional digits. strtod tries to treat 'e' as an
* exponent, but we want to treat it as a scaling suffix;
* doing this requires modifying a copy of the fraction.
*/
double fraction;
double fraction = 0.0;
f = endptr;
retval = qemu_strtod_finite(f, &endptr, &fraction);
if (retval) {
if (retval == 0 && *endptr == '.' && !isdigit(endptr[1])) {
/* If we got here, we parsed at least one digit already. */
endptr++;
} else if (memchr(f, 'e', endptr - f) || memchr(f, 'E', endptr - f)) {
endptr = nptr;
retval = -EINVAL;
goto out;
} else {
/* Extract into a 64-bit fixed-point fraction. */
valf = (uint64_t)(fraction * 0x1p64);
char *e;
const char *tail;
g_autofree char *copy = g_strdup(endptr);
e = strchr(copy, 'e');
if (e) {
*e = '\0';
}
e = strchr(copy, 'E');
if (e) {
*e = '\0';
}
/*
* If this is a floating point, we are guaranteed that '.'
* appears before any possible digits in copy. If it is
* not a floating point, strtod will fail. Either way,
* there is now no exponent in copy, so if it parses, we
* know 0.0 <= abs(result) <= 1.0 (after rounding), and
* ERANGE is only possible on underflow which is okay.
*/
retval = qemu_strtod_finite(copy, &tail, &fraction);
endptr += tail - copy;
if (signbit(fraction)) {
retval = -ERANGE;
goto out;
}
}
/* Extract into a 64-bit fixed-point fraction. */
if (fraction == 1.0) {
if (val == UINT64_MAX) {
retval = -ERANGE;
goto out;
}
val++;
} else if (retval == -ERANGE) {
/* See comments above about underflow */
valf = 1;
retval = 0;
} else {
/* We want non-zero valf for any non-zero fraction */
valf = (uint64_t)(fraction * 0x1p64);
if (valf == 0 && fraction > 0.0) {
valf = 1;
}
}
}
if (retval) {
goto out;
}
c = *endptr;
mul = suffix_mul(c, unit);