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config API: add "string" version of *_value_multi(), fix segfaults

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Fix numerous and mostly long-standing segfaults in consumers of
the *_config_*value_multi() API. As discussed in the preceding commit
an empty key in the config syntax yields a "NULL" string, which these
users would give to strcmp() (or similar), resulting in segfaults.

As this change shows, most users users of the *_config_*value_multi()
API didn't really want such an an unsafe and low-level API, let's give
them something with the safety of git_config_get_string() instead.

This fix is similar to what the *_string() functions and others
acquired in[1] and [2]. Namely introducing and using a safer
"*_get_string_multi()" variant of the low-level "_*value_multi()"
function.

This fixes segfaults in code introduced in:

  - d811c8e17c (versionsort: support reorder prerelease suffixes, 2015-02-26)
  - c026557a37 (versioncmp: generalize version sort suffix reordering, 2016-12-08)
  - a086f921a7 (submodule: decouple url and submodule interest, 2017-03-17)
  - a6be5e6764 (log: add log.excludeDecoration config option, 2020-04-16)
  - 92156291ca (log: add default decoration filter, 2022-08-05)
  - 50a044f1e4 (gc: replace config subprocesses with API calls, 2022-09-27)

There are now two users ofthe low-level API:

- One in "builtin/for-each-repo.c", which we'll convert in a
  subsequent commit.

- The "t/helper/test-config.c" code added in [3].

As seen in the preceding commit we need to give the
"t/helper/test-config.c" caller these "NULL" entries.

We could also alter the underlying git_configset_get_value_multi()
function to be "string safe", but doing so would leave no room for
other variants of "*_get_value_multi()" that coerce to other types.

Such coercion can't be built on the string version, since as we've
established "NULL" is a true value in the boolean context, but if we
coerced it to "" for use in a list of strings it'll be subsequently
coerced to "false" as a boolean.

The callback pattern being used here will make it easy to introduce
e.g. a "multi" variant which coerces its values to "bool", "int",
"path" etc.

1. 40ea4ed903 (Add config_error_nonbool() helper function,
   2008-02-11)
2. 6c47d0e8f3 (config.c: guard config parser from value=NULL,
   2008-02-11).
3. 4c715ebb96 (test-config: add tests for the config_set API,
   2014-07-28)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Ævar Arnfjörð Bjarmason
2023-03-28 16:04:27 +02:00
committed by Junio C Hamano
parent 1c7e239bd0
commit 9e2d884d0f
12 changed files with 105 additions and 22 deletions
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4
builtin/log.c
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@ -184,8 +184,8 @@ static void set_default_decoration_filter(struct decoration_filter *decoration_f
struct string_list *include = decoration_filter->include_ref_pattern;
const struct string_list *config_exclude;
if (!git_config_get_value_multi("log.excludeDecoration",
&config_exclude)) {
if (!git_config_get_string_multi("log.excludeDecoration",
&config_exclude)) {
struct string_list_item *item;
for_each_string_list_item(item, config_exclude)
string_list_append(decoration_filter->exclude_ref_config_pattern,