Skip to content

Commit

Permalink
cutils: Improve qemu_strtosz handling of fractions
Browse files Browse the repository at this point in the history 
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: cf923b7 ("utils: Improve qemu_strtosz() to have 64 bits of precision", 6.0.0)
Fixes: 7625a1e ("utils: Use fixed-point arithmetic in qemu_strtosz", 6.0.0)
Signed-off-by: Eric Blake <[email protected]>
Reviewed-by: Hanna Czenczek <[email protected]>
Message-Id: <[email protected]>
[eblake: tweak function comment for accuracy]
  • Loading branch information
@ebblake
ebblake committed Jun 2, 2023
1 parent c25b168 commit 42cc08d
Show file tree
Hide file tree
Showing 2 changed files with 87 additions and 53 deletions.
50 changes: 19 additions & 31 deletions tests/unit/test-cutils.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3408,19 +3408,18 @@ static void test_qemu_strtosz_float(void)
/* An empty fraction tail is tolerated */
do_strtosz("1.k", 0, 1024, 3);

/* FIXME An empty fraction head should be tolerated */
do_strtosz(" .5k", -EINVAL /* FIXME 0 */, 0 /* FIXME 512 */,
0 /* FIXME 4 */);
/* An empty fraction head is tolerated */
do_strtosz(" .5k", 0, 512, 4);

/* For convenience, we permit values that are not byte-exact */
do_strtosz("12.345M", 0, (uint64_t) (12.345 * MiB + 0.5), 7);

/* FIXME Fraction tail should round correctly */
/* Fraction tail can round up */
do_strtosz("1.9999k", 0, 2048, 7);
do_strtosz("1.9999999999999999999999999999999999999999999999999999k", 0,
1024 /* FIXME 2048 */, 55);
2048, 55);

/* FIXME ERANGE underflow in the fraction tail should not matter for 'k' */
/* ERANGE underflow in the fraction tail does not matter for 'k' */
do_strtosz("1."
"00000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000000000000000000000"
Expand All @@ -3429,7 +3428,7 @@ static void test_qemu_strtosz_float(void)
"00000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000000000000000000000"
"1k", 0, 1 /* FIXME 1024 */, 354);
"1k", 0, 1024, 354);
}

static void test_qemu_strtosz_invalid(void)
Expand All @@ -3453,10 +3452,9 @@ static void test_qemu_strtosz_invalid(void)
do_strtosz("1.1B", -EINVAL, 0, 0);
do_strtosz("1.1", -EINVAL, 0, 0);

/* FIXME underflow in the fraction tail should matter for 'B' */
/* 'B' cannot have any nonzero fraction, even with rounding or underflow */
do_strtosz("1.00001B", -EINVAL, 0, 0);
do_strtosz("1.00000000000000000001B", 0 /* FIXME -EINVAL */,
1 /* FIXME 0 */, 23 /* FIXME 0 */);
do_strtosz("1.00000000000000000001B", -EINVAL, 0, 0);
do_strtosz("1."
"00000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000000000000000000000"
Expand All @@ -3465,8 +3463,7 @@ static void test_qemu_strtosz_invalid(void)
"00000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000000000000000000000"
"1B", 0 /* FIXME -EINVAL */, 1 /* FIXME 0 */,
354 /* FIXME 0 */);
"1B", -EINVAL, 0, 0);

/* No hex fractions */
do_strtosz("0x1.8k", -EINVAL, 0, 0);
Expand Down Expand Up @@ -3512,28 +3509,20 @@ static void test_qemu_strtosz_trailing(void)
do_strtosz_full("123-45", qemu_strtosz, 0, 123, 3, -EINVAL, 0);
do_strtosz_full(" 123 - 45", qemu_strtosz, 0, 123, 4, -EINVAL, 0);

/* FIXME should stop parse after 'e'. No floating point exponents */
do_strtosz_full("1.5e1k", qemu_strtosz, -EINVAL /* FIXME 0 */,
0 /* FIXME EiB * 1.5 */, 0 /* FIXME 4 */,
-EINVAL, 0);
do_strtosz_full("1.5E+0k", qemu_strtosz, -EINVAL /* FIXME 0 */,
0 /* FIXME EiB * 1.5 */, 0 /* FIXME 4 */,
-EINVAL, 0);

/* FIXME overflow in fraction is still buggy */
do_strtosz_full("1.5E999", qemu_strtosz, 0, 1 /* FIXME EiB * 1.5 */,
2 /* FIXME 4 */, -EINVAL, 0);
/* Parse stops at 'e', which is not a floating point exponent */
do_strtosz_full("1.5e1k", qemu_strtosz, 0, EiB * 1.5, 4, -EINVAL, 0);
do_strtosz_full("1.5E+0k", qemu_strtosz, 0, EiB * 1.5, 4, -EINVAL, 0);
do_strtosz_full("1.5E999", qemu_strtosz, 0, EiB * 1.5, 4, -EINVAL, 0);
}

static void test_qemu_strtosz_erange(void)
{
/* FIXME negative values fit better as ERANGE */
/* no negative values */
do_strtosz(" -0", -ERANGE, 0, 3);
do_strtosz("-1", -ERANGE, 0, 2);
do_strtosz_full("-2M", qemu_strtosz, -ERANGE, 0, 2, -EINVAL, 0);
do_strtosz(" -.0", -EINVAL /* FIXME -ERANGE */, 0, 0 /* FIXME 4 */);
do_strtosz_full("-.1k", qemu_strtosz, -EINVAL /* FIXME -ERANGE */, 0,
0 /* FIXME 3 */, -EINVAL, 0);
do_strtosz(" -.0", -ERANGE, 0, 4);
do_strtosz_full("-.1k", qemu_strtosz, -ERANGE, 0, 3, -EINVAL, 0);
do_strtosz_full(" -."
"00000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000000000000000000000"
Expand All @@ -3542,17 +3531,16 @@ static void test_qemu_strtosz_erange(void)
"00000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000000000000000000000"
"00000000000000000000000000000000000000000000000000"
"1M", qemu_strtosz, -EINVAL /* FIXME -ERANGE */, 0,
0 /* FIXME 354 */, -EINVAL, 0);
"1M", qemu_strtosz, -ERANGE, 0, 354, -EINVAL, 0);

/* 2^64; see strtosz_simple for 2^64-1 */
do_strtosz("18446744073709551616", -ERANGE, 0, 20);

do_strtosz("20E", -ERANGE, 0, 3);

/* FIXME Fraction tail can cause ERANGE overflow */
/* Fraction tail can cause ERANGE overflow */
do_strtosz("15.9999999999999999999999999999999999999999999999999999E",
0 /* FIXME -ERANGE */, 15ULL * EiB /* FIXME 0 */, 56);
-ERANGE, 0, 56);

/* EINVAL has priority over ERANGE */
do_strtosz_full("100000Pjunk", qemu_strtosz, -ERANGE, 0, 7, -EINVAL, 0);
Expand Down
90 changes: 68 additions & 22 deletions util/cutils.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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) {
Expand All @@ -242,27 +246,69 @@ 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. */
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);
if (mul > 0) {
Expand Down

0 comments on commit 42cc08d

Please sign in to comment.