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From: "René Scharfe" <l.s.r@web.de>
To: Junio C Hamano <gitster@pobox.com>
Cc: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>,
	git@vger.kernel.org,
	Johannes Schindelin <johannes.schindelin@gmx.de>
Subject: Re: [PATCH 4/4] config: avoid calling `labs()` on too-large data type
Date: Thu, 20 Jun 2019 21:58:37 +0200	[thread overview]
Message-ID: <ebe4176d-1b51-fc82-7bce-713d098dbcf3@web.de> (raw)
In-Reply-To: <xmqq7e9ltbe2.fsf@gitster-ct.c.googlers.com>

Am 17.06.19 um 00:26 schrieb Junio C Hamano:
> René Scharfe <l.s.r@web.de> writes:
>
>>>>> To fix it, let's just "unroll" the function (i.e. negate the value if it
>>>>> is negative).
>>>>
>>>> There's also imaxabs(3).
>
> That may be true, but seeing that some platforms wants to see
> intmax_t defined in the compat/ layer, I suspect we cannot avoid
> having a copy of unrolled implementation somewhere in our code.

Right.  And if we later decide to give it a name then we could ask
Coccinelle to find the places that need converting with a semantic
patch like this:

	@@
	intmax_t i;
	@@
	- i < 0 ? -i : i
	+ imaxabs(i)

Side note: I was surprised to find that I added those labs(3) calls, in
83915ba521 ("use labs() for variables of type long instead of abs()",
2014-11-15).  Sloppy. :-/

> A patch to use unsigned_mult_overflows() here, on top of the
> "unrolled imaxabs" patch we reviewed, would be good to tie a loose
> end.

How about this?

-- >8 --
Subject: [PATCH] config: simplify unit suffix handling

parse_unit_factor() checks if a K, M or G is present after a number and
multiplies it by 2^10, 2^20 or 2^30, respectively.  One of its callers
checks if the result is smaller than the number alone to detect
overflows.  The other one passes 1 as the number and does multiplication
and overflow check itself in a similar manner.

This works, but is inconsistent, and it would break if we added support
for a bigger unit factor.  E.g. 16777217T expands to 2^64 + 2^40, which
is too big for a 64-bit number.  Modulo 2^64 we get 2^40 == 1TB, which
is bigger than the raw number 16777217 == 2^24 + 1, so the overflow
would go undetected by that method.

Move the multiplication out of parse_unit_factor() and rename it to
get_unit_factor() to signify its reduced functionality.  This partially
reverts c8deb5a146 ("Improve error messages when int/long cannot be
parsed from config", 2007-12-25), but keeps the improved error messages.
Use a return value of 0 to signal an invalid suffix.

And use unsigned_mult_overflows to check for an overflow *before* doing
the actual multiplication, which is simpler and can deal with larger
unit factors.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
Patch generated with --function-context for easier reviewing.

 config.c | 39 ++++++++++++++++++---------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/config.c b/config.c
index 01c6e9df23..61a8bbb5cd 100644
--- a/config.c
+++ b/config.c
@@ -834,51 +834,46 @@ static int git_parse_source(config_fn_t fn, void *data,
 	return error_return;
 }

-static int parse_unit_factor(const char *end, uintmax_t *val)
+static uintmax_t get_unit_factor(const char *end)
 {
 	if (!*end)
 		return 1;
-	else if (!strcasecmp(end, "k")) {
-		*val *= 1024;
-		return 1;
-	}
-	else if (!strcasecmp(end, "m")) {
-		*val *= 1024 * 1024;
-		return 1;
-	}
-	else if (!strcasecmp(end, "g")) {
-		*val *= 1024 * 1024 * 1024;
-		return 1;
-	}
+	if (!strcasecmp(end, "k"))
+		return 1024;
+	if (!strcasecmp(end, "m"))
+		return 1024 * 1024;
+	if (!strcasecmp(end, "g"))
+		return 1024 * 1024 * 1024;
 	return 0;
 }

 static int git_parse_signed(const char *value, intmax_t *ret, intmax_t max)
 {
 	if (value && *value) {
 		char *end;
 		intmax_t val;
 		uintmax_t uval;
-		uintmax_t factor = 1;
+		uintmax_t factor;

 		errno = 0;
 		val = strtoimax(value, &end, 0);
 		if (errno == ERANGE)
 			return 0;
-		if (!parse_unit_factor(end, &factor)) {
+		factor = get_unit_factor(end);
+		if (!factor) {
 			errno = EINVAL;
 			return 0;
 		}
 		uval = val < 0 ? -val : val;
-		uval *= factor;
-		if (uval > max || (val < 0 ? -val : val) > uval) {
+		if (unsigned_mult_overflows(factor, uval) ||
+		    factor * uval > max) {
 			errno = ERANGE;
 			return 0;
 		}
 		val *= factor;
 		*ret = val;
 		return 1;
 	}
 	errno = EINVAL;
 	return 0;
 }
@@ -886,26 +881,28 @@ static int git_parse_signed(const char *value, intmax_t *ret, intmax_t max)
 static int git_parse_unsigned(const char *value, uintmax_t *ret, uintmax_t max)
 {
 	if (value && *value) {
 		char *end;
 		uintmax_t val;
-		uintmax_t oldval;
+		uintmax_t factor;

 		errno = 0;
 		val = strtoumax(value, &end, 0);
 		if (errno == ERANGE)
 			return 0;
-		oldval = val;
-		if (!parse_unit_factor(end, &val)) {
+		factor = get_unit_factor(end);
+		if (!factor) {
 			errno = EINVAL;
 			return 0;
 		}
-		if (val > max || oldval > val) {
+		if (unsigned_mult_overflows(factor, val) ||
+		    factor * val > max) {
 			errno = ERANGE;
 			return 0;
 		}
+		val *= factor;
 		*ret = val;
 		return 1;
 	}
 	errno = EINVAL;
 	return 0;
 }
--
2.22.0

  reply	other threads:[~2019-06-20 19:58 UTC|newest]

Thread overview: 90+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-13 11:49 [PATCH 0/4] Support building with GCC v8.x/v9.x Johannes Schindelin via GitGitGadget
2019-06-13 11:49 ` [PATCH 1/4] poll (mingw): allow compiling with GCC 8 and DEVELOPER=1 Johannes Schindelin via GitGitGadget
2019-06-13 11:49 ` [PATCH 2/4] kwset: allow building with GCC 8 Johannes Schindelin via GitGitGadget
2019-06-13 16:11   ` Junio C Hamano
2019-06-14  9:53   ` SZEDER Gábor
2019-06-14 10:00     ` [RFC/PATCH v1 0/4] compat/obstack: update from upstream SZEDER Gábor
2019-06-14 10:00       ` [PATCH v1 1/4] " SZEDER Gábor
2019-06-14 10:00       ` [PATCH v1 2/4] SQUASH??? compat/obstack: fix portability issues SZEDER Gábor
2019-06-14 10:00       ` [PATCH v1 3/4] SQUASH??? compat/obstack: fix build errors with Clang SZEDER Gábor
2019-06-14 10:00       ` [PATCH v1 4/4] compat/obstack: fix some sparse warnings SZEDER Gábor
2019-06-14 17:57       ` [RFC/PATCH v1 0/4] compat/obstack: update from upstream Jeff King
2019-06-14 18:19       ` Junio C Hamano
2019-06-14 20:30       ` Ramsay Jones
2019-06-14 21:24         ` Ramsay Jones
2019-06-17 18:36         ` SZEDER Gábor
2019-06-14 16:12     ` [PATCH 2/4] kwset: allow building with GCC 8 Junio C Hamano
2019-06-17 18:26       ` SZEDER Gábor
2019-06-14 22:09   ` Ævar Arnfjörð Bjarmason
2019-06-14 22:55   ` Can we just get rid of kwset & obstack in favor of optimistically using PCRE v2 JIT? Ævar Arnfjörð Bjarmason
2019-06-14 23:19     ` Ævar Arnfjörð Bjarmason
2019-06-20 10:35       ` Jeff King
2019-06-15  9:01     ` Carlo Arenas
2019-06-15 19:15     ` brian m. carlson
2019-06-15 22:14       ` Ævar Arnfjörð Bjarmason
2019-06-26  0:03         ` [RFC/PATCH 0/7] grep: move from kwset to optional PCRE v2 Ævar Arnfjörð Bjarmason
2019-06-26 14:02           ` Johannes Schindelin
2019-06-27  9:16             ` Johannes Schindelin
2019-06-27 16:27               ` Ævar Arnfjörð Bjarmason
2019-06-27 18:21                 ` Johannes Schindelin
2019-06-27 23:39           ` [PATCH v2 0/9] " Ævar Arnfjörð Bjarmason
2019-06-28  7:23             ` Ævar Arnfjörð Bjarmason
2019-06-28 16:10               ` Junio C Hamano
2019-07-01 21:20             ` [PATCH v3 00/10] " Ævar Arnfjörð Bjarmason
2019-07-01 21:31               ` Junio C Hamano
2019-07-02 11:10                 ` Ævar Arnfjörð Bjarmason
2019-07-02 12:32               ` Johannes Schindelin
2019-07-02 19:57                 ` Junio C Hamano
2019-07-03 10:08                   ` Johannes Schindelin
2019-07-03 10:25                 ` Johannes Schindelin
2019-07-03 11:27                   ` Johannes Schindelin
2019-07-01 21:20             ` [PATCH v3 01/10] log tests: test regex backends in "--encode=<enc>" tests Ævar Arnfjörð Bjarmason
2019-07-01 21:20             ` [PATCH v3 02/10] grep: don't use PCRE2?_UTF8 with "log --encoding=<non-utf8>" Ævar Arnfjörð Bjarmason
2019-07-01 21:20             ` [PATCH v3 03/10] t4210: skip more command-line encoding tests on MinGW Ævar Arnfjörð Bjarmason
2019-07-01 21:20             ` [PATCH v3 04/10] grep: inline the return value of a function call used only once Ævar Arnfjörð Bjarmason
2019-07-01 21:20             ` [PATCH v3 05/10] grep tests: move "grep binary" alongside the rest Ævar Arnfjörð Bjarmason
2019-07-01 21:20             ` [PATCH v3 06/10] grep tests: move binary pattern tests into their own file Ævar Arnfjörð Bjarmason
2019-07-01 21:20             ` [PATCH v3 07/10] grep: make the behavior for NUL-byte in patterns sane Ævar Arnfjörð Bjarmason
2019-07-01 21:20             ` [PATCH v3 08/10] grep: drop support for \0 in --fixed-strings <pattern> Ævar Arnfjörð Bjarmason
2019-07-01 21:20             ` [PATCH v3 09/10] grep: remove the kwset optimization Ævar Arnfjörð Bjarmason
2019-07-01 21:21             ` [PATCH v3 10/10] grep: use PCRE v2 for optimized fixed-string search Ævar Arnfjörð Bjarmason
2019-06-27 23:39           ` [PATCH v2 1/9] log tests: test regex backends in "--encode=<enc>" tests Ævar Arnfjörð Bjarmason
2019-06-27 23:39           ` [PATCH v2 2/9] grep: don't use PCRE2?_UTF8 with "log --encoding=<non-utf8>" Ævar Arnfjörð Bjarmason
2019-06-27 23:39           ` [PATCH v2 3/9] grep: inline the return value of a function call used only once Ævar Arnfjörð Bjarmason
2019-06-27 23:39           ` [PATCH v2 4/9] grep tests: move "grep binary" alongside the rest Ævar Arnfjörð Bjarmason
2019-06-27 23:39           ` [PATCH v2 5/9] grep tests: move binary pattern tests into their own file Ævar Arnfjörð Bjarmason
2019-06-27 23:39           ` [PATCH v2 6/9] grep: make the behavior for NUL-byte in patterns sane Ævar Arnfjörð Bjarmason
2019-06-27 23:39           ` [PATCH v2 7/9] grep: drop support for \0 in --fixed-strings <pattern> Ævar Arnfjörð Bjarmason
2019-06-27 23:39           ` [PATCH v2 8/9] grep: remove the kwset optimization Ævar Arnfjörð Bjarmason
2019-06-27 23:39           ` [PATCH v2 9/9] grep: use PCRE v2 for optimized fixed-string search Ævar Arnfjörð Bjarmason
2019-06-26  0:03         ` [RFC/PATCH 1/7] grep: inline the return value of a function call used only once Ævar Arnfjörð Bjarmason
2019-06-26  0:03         ` [RFC/PATCH 2/7] grep tests: move "grep binary" alongside the rest Ævar Arnfjörð Bjarmason
2019-06-26 14:05           ` Johannes Schindelin
2019-06-26 18:13           ` Junio C Hamano
2019-06-26  0:03         ` [RFC/PATCH 3/7] grep tests: move binary pattern tests into their own file Ævar Arnfjörð Bjarmason
2019-06-26  0:03         ` [RFC/PATCH 4/7] grep: make the behavior for \0 in patterns sane Ævar Arnfjörð Bjarmason
2019-06-27  2:03           ` brian m. carlson
2019-06-26  0:03         ` [RFC/PATCH 5/7] grep: drop support for \0 in --fixed-strings <pattern> Ævar Arnfjörð Bjarmason
2019-06-26 16:14           ` Junio C Hamano
2019-06-26  0:03         ` [RFC/PATCH 6/7] grep: remove the kwset optimization Ævar Arnfjörð Bjarmason
2019-06-26  0:03         ` [RFC/PATCH 7/7] grep: use PCRE v2 for optimized fixed-string search Ævar Arnfjörð Bjarmason
2019-06-26 14:13           ` Johannes Schindelin
2019-06-26 18:45             ` Junio C Hamano
2019-06-27  9:31               ` Johannes Schindelin
2019-06-27 18:45                 ` Johannes Schindelin
2019-06-27 19:06                   ` Junio C Hamano
2019-06-28 10:56                     ` Johannes Schindelin
2019-06-13 11:49 ` [PATCH 3/4] winansi: simplify loading the GetCurrentConsoleFontEx() function Johannes Schindelin via GitGitGadget
2019-06-13 11:49 ` [PATCH 4/4] config: avoid calling `labs()` on too-large data type Johannes Schindelin via GitGitGadget
2019-06-13 16:13   ` Junio C Hamano
2019-06-16  6:48   ` René Scharfe
2019-06-16  8:24     ` René Scharfe
2019-06-16 14:01       ` René Scharfe
2019-06-16 22:26         ` Junio C Hamano
2019-06-20 19:58           ` René Scharfe [this message]
2019-06-20 21:07             ` Junio C Hamano
2019-06-21 18:35             ` Johannes Schindelin
2019-06-22 10:03               ` René Scharfe
2019-06-22 10:03           ` [PATCH v2 1/3] config: use unsigned_mult_overflows to check for overflows René Scharfe
2019-06-22 10:03           ` [PATCH v2 2/3] config: don't multiply in parse_unit_factor() René Scharfe
2019-06-22 10:03           ` [PATCH v2 3/3] config: simplify parsing of unit factors René Scharfe

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