diff mbox series

[v3,3/3] config: allow overriding of global and system configuration

Message ID af663640ae25a95fa56adf32baf4c2e197f3eea2.1618238567.git.ps@pks.im (mailing list archive)
State Superseded
Headers show
Series config: allow overriding global/system config | expand

Commit Message

Patrick Steinhardt April 12, 2021, 2:46 p.m. UTC
In order to have git run in a fully controlled environment without any
misconfiguration, it may be desirable for users or scripts to override
global- and system-level configuration files. We already have a way of
doing this, which is to unset both HOME and XDG_CONFIG_HOME environment
variables and to set `GIT_CONFIG_NOGLOBAL=true`. This is quite kludgy,
and unsetting the first two variables likely has an impact on other
executables spawned by such a script.

The obvious way to fix this would be to introduce `GIT_CONFIG_NOGLOBAL`
as an equivalent to `GIT_CONFIG_NOSYSTEM`. But in the past, it has
turned out that this design is inflexible: we cannot test system-level
parsing of the git configuration in our test harness because there is no
way to change its location, so all tests run with `GIT_CONFIG_NOSYSTEM`
set.

Instead of doing the same mistake with `GIT_CONFIG_NOGLOBAL`, introduce
two new variables `GIT_CONFIG_GLOBAL` and `GIT_CONFIG_SYSTEM`:

    - If unset, git continues to use the usual locations.

    - If set to a specific path, we skip reading the normal
      configuration files and instead take the path.

    - If set to `/dev/null`, we do not load either global- or
      system-level configuration at all.

This implements the usecase where we want to execute code in a sanitized
environment without any potential misconfigurations via `/dev/null`, but
is more flexible and allows for more usecases than simply adding
`GIT_CONFIG_NOGLOBAL`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 Documentation/git-config.txt |  5 +++
 Documentation/git.txt        | 10 +++++
 builtin/config.c             |  6 ++-
 config.c                     | 24 ++++++++++--
 t/t1300-config.sh            | 71 ++++++++++++++++++++++++++++++++++++
 5 files changed, 112 insertions(+), 4 deletions(-)

Comments

Junio C Hamano April 12, 2021, 5:04 p.m. UTC | #1
Patrick Steinhardt <ps@pks.im> writes:

>  char *git_system_config(void)
>  {
> +	char *system_config = xstrdup_or_null(getenv("GIT_CONFIG_SYSTEM"));
> +	if (system_config) {
> +		if (!strcmp(system_config, "/dev/null"))
> +			FREE_AND_NULL(system_config);
> +		return system_config;
> +	}

I am not sure if returning NULL from this function will always be
the same as returning /dev/null on a system with functioning
/dev/null.  For example, when use_system_config is enabled,
builtin/config.c::cmd_config() assigns the NULL returned by this
function to given_config_source.file and then calls
config.c::config_with_options(), which notices that none of
use_stdin, file, or blob member of the config_source exists and
falls back to the config_sequence().

So, for the purpose of special casing "/dev/null" textually, the
above is not sufficient, I am afraid.

Let's rescind the "/dev/null gets turned into NULL" in the above
change for now.  If we truly want to cater to an installation where
open("/dev/null") fails and emulate, that needs to be done at a much
lower layer, but we do not have to go there for the purpose of this
series.

Thanks.
diff mbox series

Patch

diff --git a/Documentation/git-config.txt b/Documentation/git-config.txt
index 4b4cc5c5e8..5cddadafd2 100644
--- a/Documentation/git-config.txt
+++ b/Documentation/git-config.txt
@@ -340,6 +340,11 @@  GIT_CONFIG::
 	Using the "--global" option forces this to ~/.gitconfig. Using the
 	"--system" option forces this to $(prefix)/etc/gitconfig.
 
+GIT_CONFIG_GLOBAL::
+GIT_CONFIG_SYSTEM::
+	Take the configuration from the given files instead from global or
+	system-level configuration. See linkgit:git[1] for details.
+
 GIT_CONFIG_NOSYSTEM::
 	Whether to skip reading settings from the system-wide
 	$(prefix)/etc/gitconfig file. See linkgit:git[1] for details.
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 3a9c44987f..380422a6a9 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -670,6 +670,16 @@  for further details.
 	If this environment variable is set to `0`, git will not prompt
 	on the terminal (e.g., when asking for HTTP authentication).
 
+`GIT_CONFIG_GLOBAL`::
+`GIT_CONFIG_SYSTEM`::
+	Take the configuration from the given files instead from global or
+	system-level configuration files. If `GIT_CONFIG_SYSTEM` is set, the
+	system config file defined at build time (usually `/etc/gitconfig`)
+	will not be read. Likewise, if `GIT_CONFIG_GLOBAL` is set, neither
+	`$HOME/.gitconfig` nor `$XDG_CONFIG_HOME/git/config` will be read. Can
+	be set to `/dev/null` to skip reading configuration files of the
+	respective level.
+
 `GIT_CONFIG_NOSYSTEM`::
 	Whether to skip reading settings from the system-wide
 	`$(prefix)/etc/gitconfig` file.  This environment variable can
diff --git a/builtin/config.c b/builtin/config.c
index 865fddd6ce..9104816459 100644
--- a/builtin/config.c
+++ b/builtin/config.c
@@ -674,7 +674,10 @@  int cmd_config(int argc, const char **argv, const char *prefix)
 		char *user_config, *xdg_config;
 
 		git_global_config(&user_config, &xdg_config);
-		if (!user_config)
+		if (!user_config) {
+			if (getenv("GIT_CONFIG_GLOBAL"))
+				die(_("GIT_CONFIG_GLOBAL=/dev/null set"));
+
 			/*
 			 * It is unknown if HOME/.gitconfig exists, so
 			 * we do not know if we should write to XDG
@@ -682,6 +685,7 @@  int cmd_config(int argc, const char **argv, const char *prefix)
 			 * is set and points at a sane location.
 			 */
 			die(_("$HOME not set"));
+		}
 
 		given_config_source.scope = CONFIG_SCOPE_GLOBAL;
 
diff --git a/config.c b/config.c
index ebff58aa57..ed46eda997 100644
--- a/config.c
+++ b/config.c
@@ -1846,13 +1846,31 @@  static int git_config_from_blob_ref(config_fn_t fn,
 
 char *git_system_config(void)
 {
+	char *system_config = xstrdup_or_null(getenv("GIT_CONFIG_SYSTEM"));
+	if (system_config) {
+		if (!strcmp(system_config, "/dev/null"))
+			FREE_AND_NULL(system_config);
+		return system_config;
+	}
 	return system_path(ETC_GITCONFIG);
 }
 
-void git_global_config(char **user_config, char **xdg_config)
+void git_global_config(char **user_out, char **xdg_out)
 {
-	*user_config = expand_user_path("~/.gitconfig", 0);
-	*xdg_config = xdg_config_home("config");
+	char *user_config = xstrdup_or_null(getenv("GIT_CONFIG_GLOBAL"));
+	char *xdg_config = NULL;
+
+	if (user_config) {
+		if (!strcmp(user_config, "/dev/null"))
+			FREE_AND_NULL(user_config);
+		xdg_config = NULL;
+	} else {
+		user_config = expand_user_path("~/.gitconfig", 0);
+		xdg_config = xdg_config_home("config");
+	}
+
+	*user_out = user_config;
+	*xdg_out = xdg_config;
 }
 
 /*
diff --git a/t/t1300-config.sh b/t/t1300-config.sh
index e0dd5d65ce..17f1b78c01 100755
--- a/t/t1300-config.sh
+++ b/t/t1300-config.sh
@@ -2059,6 +2059,77 @@  test_expect_success '--show-scope with --show-origin' '
 	test_cmp expect output
 '
 
+test_expect_success 'override global and system config' '
+	test_when_finished rm -f "$HOME"/.config/git &&
+
+	cat >"$HOME"/.gitconfig <<-EOF &&
+	[home]
+		config = true
+	EOF
+	mkdir -p "$HOME"/.config/git &&
+	cat >"$HOME"/.config/git/config <<-EOF &&
+	[xdg]
+		config = true
+	EOF
+	cat >.git/config <<-EOF &&
+	[local]
+		config = true
+	EOF
+	cat >custom-global-config <<-EOF &&
+	[global]
+		config = true
+	EOF
+	cat >custom-system-config <<-EOF &&
+	[system]
+		config = true
+	EOF
+
+	cat >expect <<-EOF &&
+	global	xdg.config=true
+	global	home.config=true
+	local	local.config=true
+	EOF
+	git config --show-scope --list >output &&
+	test_cmp expect output &&
+
+	sane_unset GIT_CONFIG_NOSYSTEM &&
+
+	cat >expect <<-EOF &&
+	system	system.config=true
+	global	global.config=true
+	local	local.config=true
+	EOF
+	GIT_CONFIG_SYSTEM=custom-system-config GIT_CONFIG_GLOBAL=custom-global-config \
+		git config --show-scope --list >output &&
+	test_cmp expect output &&
+
+	cat >expect <<-EOF &&
+	local	local.config=true
+	EOF
+	GIT_CONFIG_SYSTEM=/dev/null GIT_CONFIG_GLOBAL=/dev/null git config --show-scope --list >output &&
+	test_cmp expect output
+'
+
+test_expect_success 'override global and system config with missing file' '
+	sane_unset GIT_CONFIG_NOSYSTEM &&
+	test_must_fail env GIT_CONFIG_GLOBAL=does-not-exist GIT_CONFIG_SYSTEM=/dev/null git config --global --list >actual &&
+	test_must_fail env GIT_CONFIG_GLOBAL=/dev/null GIT_CONFIG_SYSTEM=does-not-exist git config --system --list >actual &&
+	GIT_CONFIG_GLOBAL=does-not-exist GIT_CONFIG_SYSTEM=does-not-exist git version
+'
+
+test_expect_success 'write to overridden global and system config' '
+	cat >expect <<EOF &&
+[config]
+	key = value
+EOF
+
+	GIT_CONFIG_GLOBAL=write-to-global git config --global config.key value &&
+	test_cmp expect write-to-global &&
+
+	GIT_CONFIG_SYSTEM=write-to-system git config --system config.key value &&
+	test_cmp expect write-to-system
+'
+
 for opt in --local --worktree
 do
 	test_expect_success "$opt requires a repo" '