[PATCH v2 2/2] config: allow specifying config entries via envvar pairs

[Patrick Steinhardt <ps@pks.im>]

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While we currently have the `GIT_CONFIG_PARAMETERS` environment variable
which can be used to pass runtime configuration data to git processes,
it's an internal implementation detail and not supposed to be used by
end users.

Next to being for internal use only, this way of passing config entries
has a major downside: the config keys need to be parsed as they contain
both key and value in a single variable. As such, it is left to the user
to escape any potentially harmful characters in the value, which is
quite hard to do if values are controlled by a third party.

This commit thus adds a new way of adding config entries via the
environment which gets rid of this shortcoming. If the user passes the
`GIT_CONFIG_COUNT=$n` environment variable, Git will parse environment
variable pairs `GIT_CONFIG_KEY_$i` and `GIT_CONFIG_VALUE_$i` for each
`i` in `[0,n)`.

While the same can be achieved with `git -c <name>=<value>`, one may
wish to not do so for potentially sensitive information. E.g. if one
wants to set `http.extraHeader` to contain an authentication token,
doing so via `-c` would trivially leak those credentials via e.g. ps(1),
which typically also shows command arguments.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-config.txt |   9 +++
 cache.h                      |   1 +
 config.c                     |  72 +++++++++++++++++++-----
 environment.c                |   1 +
 t/t1300-config.sh            | 105 ++++++++++++++++++++++++++++++++++-
 5 files changed, 173 insertions(+), 15 deletions(-)

diff --git a/Documentation/git-config.txt b/Documentation/git-config.txt
index 7573160f21..84ae9b51a3 100644
--- a/Documentation/git-config.txt
+++ b/Documentation/git-config.txt
@@ -335,6 +335,15 @@ GIT_CONFIG_NOSYSTEM::
 	Whether to skip reading settings from the system-wide
 	$(prefix)/etc/gitconfig file. See linkgit:git[1] for details.
 
+GIT_CONFIG_COUNT,GIT_CONFIG_KEY_<n>,GIT_CONFIG_VALUE_<n>::
+	If GIT_CONFIG_COUNT is set to a positive number, all environment pairs
+	GIT_CONFIG_KEY_<n> and GIT_CONFIG_VALUE_<n> up to that number will be
+	added to the process's runtime configuration. The config pairs are
+	zero-indexed. Any missing key or value is treated as an error. An empty
+	GIT_CONFIG_COUNT is treated the same as GIT_CONFIG_COUNT=0, namely no
+	pairs are processed. Config entries set this way have command scope,
+	but will be overridden by any explicit options passed via `git -c`.
+
 See also <<FILES>>.
 
 
diff --git a/cache.h b/cache.h
index c0072d43b1..8a36146337 100644
--- a/cache.h
+++ b/cache.h
@@ -472,6 +472,7 @@ static inline enum object_type object_type(unsigned int mode)
 #define TEMPLATE_DIR_ENVIRONMENT "GIT_TEMPLATE_DIR"
 #define CONFIG_ENVIRONMENT "GIT_CONFIG"
 #define CONFIG_DATA_ENVIRONMENT "GIT_CONFIG_PARAMETERS"
+#define CONFIG_COUNT_ENVIRONMENT "GIT_CONFIG_COUNT"
 #define EXEC_PATH_ENVIRONMENT "GIT_EXEC_PATH"
 #define CEILING_DIRECTORIES_ENVIRONMENT "GIT_CEILING_DIRECTORIES"
 #define NO_REPLACE_OBJECTS_ENVIRONMENT "GIT_NO_REPLACE_OBJECTS"
diff --git a/config.c b/config.c
index 3281b1374e..5da1ae16c9 100644
--- a/config.c
+++ b/config.c
@@ -484,38 +484,82 @@ int git_config_parse_parameter(const char *text,
 
 int git_config_from_parameters(config_fn_t fn, void *data)
 {
-	const char *env = getenv(CONFIG_DATA_ENVIRONMENT);
+	const char *env;
+	struct strbuf envvar = STRBUF_INIT;
 	int ret = 0;
-	char *envw;
+	char *envw = NULL;
 	const char **argv = NULL;
-	int nr = 0, alloc = 0;
 	int i;
 	struct config_source source;
 
-	if (!env)
-		return 0;
-
 	memset(&source, 0, sizeof(source));
 	source.prev = cf;
 	source.origin_type = CONFIG_ORIGIN_CMDLINE;
 	cf = &source;
 
-	/* sq_dequote will write over it */
-	envw = xstrdup(env);
+	env = getenv(CONFIG_COUNT_ENVIRONMENT);
+	if (env) {
+		unsigned long count;
+		char *endp;
 
-	if (sq_dequote_to_argv(envw, &argv, &nr, &alloc) < 0) {
-		ret = error(_("bogus format in %s"), CONFIG_DATA_ENVIRONMENT);
-		goto out;
+		count = strtoul(env, &endp, 10);
+		if (*endp) {
+			ret = error(_("bogus count in %s"), CONFIG_COUNT_ENVIRONMENT);
+			goto out;
+		}
+		if (count > INT_MAX) {
+			ret = error(_("too many entries in %s"), CONFIG_COUNT_ENVIRONMENT);
+			goto out;
+		}
+
+		for (i = 0; i < count; i++) {
+			const char *key, *value;
+
+			strbuf_addf(&envvar, "GIT_CONFIG_KEY_%d", i);
+			key = getenv(envvar.buf);
+			if (!key) {
+				ret = error(_("missing config key %s"), envvar.buf);
+				goto out;
+			}
+			strbuf_reset(&envvar);
+
+			strbuf_addf(&envvar, "GIT_CONFIG_VALUE_%d", i);
+			value = getenv(envvar.buf);
+			if (!value) {
+				ret = error(_("missing config value %s"), envvar.buf);
+				goto out;
+			}
+			strbuf_reset(&envvar);
+
+			if (config_parse_pair(key, value, fn, data) < 0) {
+				ret = -1;
+				goto out;
+			}
+		}
 	}
 
-	for (i = 0; i < nr; i++) {
-		if (git_config_parse_parameter(argv[i], fn, data) < 0) {
-			ret = -1;
+	env = getenv(CONFIG_DATA_ENVIRONMENT);
+	if (env) {
+		int nr = 0, alloc = 0;
+
+		/* sq_dequote will write over it */
+		envw = xstrdup(env);
+
+		if (sq_dequote_to_argv(envw, &argv, &nr, &alloc) < 0) {
+			ret = error(_("bogus format in %s"), CONFIG_DATA_ENVIRONMENT);
 			goto out;
 		}
+
+		for (i = 0; i < nr; i++) {
+			if (git_config_parse_parameter(argv[i], fn, data) < 0) {
+				ret = -1;
+				goto out;
+			}
+		}
 	}
 
 out:
+	strbuf_release(&envvar);
 	free(argv);
 	free(envw);
 	cf = source.prev;
diff --git a/environment.c b/environment.c
index bb518c61cd..e94eca92f3 100644
--- a/environment.c
+++ b/environment.c
@@ -116,6 +116,7 @@ const char * const local_repo_env[] = {
 	ALTERNATE_DB_ENVIRONMENT,
 	CONFIG_ENVIRONMENT,
 	CONFIG_DATA_ENVIRONMENT,
+	CONFIG_COUNT_ENVIRONMENT,
 	DB_ENVIRONMENT,
 	GIT_DIR_ENVIRONMENT,
 	GIT_WORK_TREE_ENVIRONMENT,
diff --git a/t/t1300-config.sh b/t/t1300-config.sh
index 825d9a184f..8c90cca79d 100755
--- a/t/t1300-config.sh
+++ b/t/t1300-config.sh
@@ -1316,6 +1316,107 @@ test_expect_success 'detect bogus GIT_CONFIG_PARAMETERS' '
 		git config --get-regexp "env.*"
 '
 
+test_expect_success 'git config handles environment config pairs' '
+	GIT_CONFIG_COUNT=2 \
+		GIT_CONFIG_KEY_0="pair.one" GIT_CONFIG_VALUE_0="foo" \
+		GIT_CONFIG_KEY_1="pair.two" GIT_CONFIG_VALUE_1="bar" \
+		git config --get-regexp "pair.*" >actual &&
+	cat >expect <<-EOF &&
+	pair.one foo
+	pair.two bar
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'git config ignores pairs without count' '
+	test_must_fail env GIT_CONFIG_KEY_0="pair.one" GIT_CONFIG_VALUE_0="value" \
+		git config pair.one 2>error &&
+	test_must_be_empty error
+'
+
+test_expect_success 'git config ignores pairs with zero count' '
+	test_must_fail env \
+		GIT_CONFIG_COUNT=0 \
+		GIT_CONFIG_KEY_0="pair.one" GIT_CONFIG_VALUE_0="value" \
+		git config pair.one
+'
+
+test_expect_success 'git config ignores pairs exceeding count' '
+	GIT_CONFIG_COUNT=1 \
+		GIT_CONFIG_KEY_0="pair.one" GIT_CONFIG_VALUE_0="value" \
+		GIT_CONFIG_KEY_1="pair.two" GIT_CONFIG_VALUE_1="value" \
+		git config --get-regexp "pair.*" >actual &&
+	cat >expect <<-EOF &&
+	pair.one value
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'git config ignores pairs with zero count' '
+	test_must_fail env \
+		GIT_CONFIG_COUNT=0 GIT_CONFIG_KEY_0="pair.one" GIT_CONFIG_VALUE_0="value" \
+		git config pair.one >error &&
+	test_must_be_empty error
+'
+
+test_expect_success 'git config ignores pairs with empty count' '
+	test_must_fail env \
+		GIT_CONFIG_COUNT= GIT_CONFIG_KEY_0="pair.one" GIT_CONFIG_VALUE_0="value" \
+		git config pair.one >error &&
+	test_must_be_empty error
+'
+
+test_expect_success 'git config fails with invalid count' '
+	test_must_fail env GIT_CONFIG_COUNT=10a git config --list 2>error &&
+	test_i18ngrep "bogus count" error &&
+	test_must_fail env GIT_CONFIG_COUNT=9999999999999999 git config --list 2>error &&
+	test_i18ngrep "too many entries" error
+'
+
+test_expect_success 'git config fails with missing config key' '
+	test_must_fail env GIT_CONFIG_COUNT=1 GIT_CONFIG_VALUE_0="value" \
+		git config --list 2>error &&
+	test_i18ngrep "missing config key" error
+'
+
+test_expect_success 'git config fails with missing config value' '
+	test_must_fail env GIT_CONFIG_COUNT=1 GIT_CONFIG_KEY_0="pair.one" \
+		git config --list 2>error &&
+	test_i18ngrep "missing config value" error
+'
+
+test_expect_success 'git config fails with invalid config pair key' '
+	test_must_fail env GIT_CONFIG_COUNT=1 \
+		GIT_CONFIG_KEY_0= GIT_CONFIG_VALUE_0=value \
+		git config --list &&
+	test_must_fail env GIT_CONFIG_COUNT=1 \
+		GIT_CONFIG_KEY_0=missing-section GIT_CONFIG_VALUE_0=value \
+		git config --list
+'
+
+test_expect_success 'environment overrides config file' '
+	test_when_finished "rm -f .git/config" &&
+	cat >.git/config <<-EOF &&
+	[pair]
+	one = value
+	EOF
+	GIT_CONFIG_COUNT=1 GIT_CONFIG_KEY_0=pair.one GIT_CONFIG_VALUE_0=override \
+		git config pair.one >actual &&
+	cat >expect <<-EOF &&
+	override
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'command line overrides environment config' '
+	GIT_CONFIG_COUNT=1 GIT_CONFIG_KEY_0=pair.one GIT_CONFIG_VALUE_0=value \
+		git -c pair.one=override config pair.one >actual &&
+	cat >expect <<-EOF &&
+	override
+	EOF
+	test_cmp expect actual
+'
+
 test_expect_success 'git config --edit works' '
 	git config -f tmp test.value no &&
 	echo test.value=yes >expect &&
@@ -1661,9 +1762,11 @@ test_expect_success '--show-origin with --list' '
 	file:.git/config	user.override=local
 	file:.git/config	include.path=../include/relative.include
 	file:.git/../include/relative.include	user.relative=include
+	command line:	user.environ=true
 	command line:	user.cmdline=true
 	EOF
-	git -c user.cmdline=true config --list --show-origin >output &&
+	GIT_CONFIG_COUNT=1 GIT_CONFIG_KEY_0=user.environ GIT_CONFIG_VALUE_0=true\
+		git -c user.cmdline=true config --list --show-origin >output &&
 	test_cmp expect output
 '
 
-- 
2.29.2


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