safe.bareRepository: default to "explicit" with WITH_BREAKING_CHANGES

Documentation/BreakingChanges.adoc

@@ -216,6 +216,30 @@ would be significant, we may decide to defer this change to a subsequent minor
 release. This evaluation will also take into account our own experience with
 how painful it is to keep Rust an optional component.
 
+* The default value of `safe.bareRepository` will change from `all` to
+  `explicit`. It is all too easy for an attacker to trick a user into cloning a
+  repository that contains an embedded bare repository with malicious hooks
+  configured. If the user enters that subdirectory and runs any Git command, Git
+  discovers the bare repository and the hooks fire. The user does not even need
+  to run a Git command explicitly: many shell prompts run `git status` in the
+  background to display branch and dirty state information, and `git status` in
+  turn may invoke the fsmonitor hook if so configured, making the user
+  vulnerable the moment they `cd` into the directory. The `safe.bareRepository`
+  configuration variable was introduced in 8959555cee (setup_git_directory():
+  add an owner check for the top-level directory, 2022-03-02) with a default of
+  `all` to preserve backwards compatibility.
++
+Changing the default to `explicit` means that Git will refuse to work with bare
+repositories that are discovered implicitly by walking up the directory tree.
+Bare repositories specified explicitly via the `--git-dir` command-line option
+or the `GIT_DIR` environment variable continue to work regardless of this
+setting. Repositories that look like a `.git` directory, a worktree, or a
+submodule directory are also unaffected.
++
+Users who rely on implicit discovery of bare repositories can restore the
+previous behavior by setting `safe.bareRepository=all` in their global or
+system configuration.
+
 === Removals
 
 * Support for grafting commits has long been superseded by git-replace(1).

Documentation/config/safe.adoc

@@ -2,17 +2,23 @@ safe.bareRepository::
 	Specifies which bare repositories Git will work with. The currently
 	supported values are:
 +
-* `all`: Git works with all bare repositories. This is the default.
+* `all`: Git works with all bare repositories. This is the default in
+  Git 2.x.
 * `explicit`: Git only works with bare repositories specified via
   the top-level `--git-dir` command-line option, or the `GIT_DIR`
-  environment variable (see linkgit:git[1]).
+  environment variable (see linkgit:git[1]). This will be the default
+  in Git 3.0.
 +
 If you do not use bare repositories in your workflow, then it may be
 beneficial to set `safe.bareRepository` to `explicit` in your global
 config. This will protect you from attacks that involve cloning a
 repository that contains a bare repository and running a Git command
 within that directory.
 +
+If you use bare repositories regularly and want to preserve the current
+behavior after upgrading to Git 3.0, set `safe.bareRepository` to `all`
+in your global or system config.
++
 This config setting is only respected in protected configuration (see
 <<SCOPES>>). This prevents untrusted repositories from tampering with
 this value.

contrib/subtree/t/t7900-subtree.sh

@@ -1005,7 +1005,7 @@ test_expect_success 'push sub dir/ with --rejoin from scratch' '
 		git init --bare "sub proj.git" &&
 		git subtree push --prefix="sub dir" --rejoin ./"sub proj.git" from-mainline &&
 		test "$(last_commit_subject)" = "Split '\''sub dir/'\'' into commit '\''$split_hash'\''" &&
-		test "$split_hash" = "$(git -C "sub proj.git" rev-parse --verify refs/heads/from-mainline)"
+		test "$split_hash" = "$(git --git-dir="sub proj.git" rev-parse --verify refs/heads/from-mainline)"
 	)
 '
 

git-p4.py

@@ -4360,6 +4360,7 @@ def run(self, args):
         init_cmd = ["git", "init"]
         if self.cloneBare:
             init_cmd.append("--bare")
+            os.environ["GIT_DIR"] = os.getcwd()
         retcode = subprocess.call(init_cmd)
         if retcode:
             raise subprocess.CalledProcessError(retcode, init_cmd)

setup.c

@@ -1485,7 +1485,11 @@ static int allowed_bare_repo_cb(const char *key, const char *value,
 
 static enum allowed_bare_repo get_allowed_bare_repo(void)
 {
+#ifdef WITH_BREAKING_CHANGES
+	enum allowed_bare_repo result = ALLOWED_BARE_REPO_EXPLICIT;
+#else
 	enum allowed_bare_repo result = ALLOWED_BARE_REPO_ALL;
+#endif
 	git_protected_config(allowed_bare_repo_cb, &result);
 	return result;
 }

t/annotate-tests.sh

@@ -86,7 +86,7 @@ test_expect_success 'blame with --contents' '
 test_expect_success 'blame with --contents in a bare repo' '
 	git clone --bare . bare-contents.git &&
 	(
-		cd bare-contents.git &&
+		cd bare-contents.git && GIT_DIR=. && export GIT_DIR &&
 		echo "1A quick brown fox jumps over the" >contents &&
 		check_count --contents=contents A 1
 	)
@@ -101,7 +101,7 @@ test_expect_success 'blame with --contents changed' '
 test_expect_success 'blame in a bare repo without starting commit' '
 	git clone --bare . bare.git &&
 	(
-		cd bare.git &&
+		cd bare.git && GIT_DIR=. && export GIT_DIR &&
 		check_count A 2
 	)
 '

t/helper/test-tool.c

@@ -3,9 +3,10 @@
 #include "test-tool-utils.h"
 #include "trace2.h"
 #include "parse-options.h"
+#include "environment.h"
 
 static const char * const test_tool_usage[] = {
-	"test-tool [-C <directory>] <command [<arguments>...]]",
+	"test-tool [-C <directory>] [--git-dir=<path>] <command [<arguments>...]]",
 	NULL
 };
 
@@ -107,9 +108,12 @@ static NORETURN void die_usage(void)
 int cmd_main(int argc, const char **argv)
 {
 	const char *working_directory = NULL;
+	const char *git_dir = NULL;
 	struct option options[] = {
 		OPT_STRING('C', NULL, &working_directory, "directory",
 			   "change the working directory"),
+		OPT_STRING(0, "git-dir", &git_dir, "path",
+			   "set the path to the repository"),
 		OPT_END()
 	};
 
@@ -123,6 +127,8 @@ int cmd_main(int argc, const char **argv)
 
 	if (working_directory && chdir(working_directory) < 0)
 		die("Could not cd to '%s'", working_directory);
+	if (git_dir)
+		setenv(GIT_DIR_ENVIRONMENT, git_dir, 1);
 
 	for (size_t i = 0; i < ARRAY_SIZE(cmds); i++) {
 		if (!strcmp(cmds[i].name, argv[1])) {

t/lib-bitmap.sh

@@ -207,7 +207,7 @@ basic_bitmap_tests () {
 		rm -fr partial-clone.git &&
 		git clone --no-local --bare --filter=blob:none . partial-clone.git &&
 		(
-			cd partial-clone.git &&
+			cd partial-clone.git && GIT_DIR=. && export GIT_DIR &&
 			pack=$(echo objects/pack/*.pack) &&
 			git verify-pack -v "$pack" >have &&
 			awk "/blob/ { print \$1 }" <have >blobs &&

t/lib-commit-graph.sh

@@ -22,23 +22,41 @@ graph_git_two_modes() {
 # NOTE: it is a bug to call this function with <directory> containing
 # any characters in $IFS.
 graph_git_behavior() {
+	BARE=
+	if test "$1" = "--bare"
+	then
+		BARE=t
+		shift
+	fi
 	MSG=$1
 	DIR=$2
 	BRANCH=$3
 	COMPARE=$4
 	test_expect_success "check normal git operations: $MSG" '
-		graph_git_two_modes "${DIR:+-C $DIR} log --oneline $BRANCH" &&
-		graph_git_two_modes "${DIR:+-C $DIR} log --topo-order $BRANCH" &&
-		graph_git_two_modes "${DIR:+-C $DIR} log --graph $COMPARE..$BRANCH" &&
-		graph_git_two_modes "${DIR:+-C $DIR} branch -vv" &&
-		graph_git_two_modes "${DIR:+-C $DIR} merge-base -a $BRANCH $COMPARE"
+		if test -n "$BARE"
+		then
+			DIR_ARGS="${DIR:+--git-dir=$DIR}"
+		else
+			DIR_ARGS="${DIR:+-C $DIR}"
+		fi &&
+		graph_git_two_modes "$DIR_ARGS log --oneline $BRANCH" &&
+		graph_git_two_modes "$DIR_ARGS log --topo-order $BRANCH" &&
+		graph_git_two_modes "$DIR_ARGS log --graph $COMPARE..$BRANCH" &&
+		graph_git_two_modes "$DIR_ARGS branch -vv" &&
+		graph_git_two_modes "$DIR_ARGS merge-base -a $BRANCH $COMPARE"
 	'
 }
 
 graph_read_expect() {
 	OPTIONAL=""
 	NUM_CHUNKS=3
 	DIR="."
+	BARE=
+	if test "$1" = "--bare"
+	then
+		BARE=t
+		shift
+	fi
 	if test "$1" = -C
 	then
 		shift
@@ -68,6 +86,10 @@ graph_read_expect() {
 	EOF
 	(
 		cd "$DIR" &&
+		if test -n "$BARE"
+		then
+			GIT_DIR=. && export GIT_DIR
+		fi &&
 		test-tool read-graph >output &&
 		test_cmp expect output
 	)

t/lib-diff-alternative.sh

@@ -131,14 +131,14 @@ EOF
 	'
 
 	test_expect_success "diff from attributes with bare repo with source" '
-		git -C bare.git --attr-source=branchA -c diff.driver.algorithm=myers \
+		git --git-dir=bare.git --attr-source=branchA -c diff.driver.algorithm=myers \
 			-c diff.driverA.algorithm=$STRATEGY \
 			diff HEAD:file1 HEAD:file2 >output &&
 		test_cmp expect output
 	'
 
 	test_expect_success "diff from attributes with bare repo with invalid source" '
-		test_must_fail git -C bare.git --attr-source=invalid-branch diff \
+		test_must_fail git --git-dir=bare.git --attr-source=invalid-branch diff \
 			HEAD:file1 HEAD:file2
 	'
 

t/lib-httpd.sh

@@ -259,7 +259,7 @@ test_http_push_nonff () {
 
 	test_expect_success 'non-fast-forward push fails' '
 		cd "$REMOTE_REPO" &&
-		HEAD=$(git rev-parse --verify HEAD) &&
+		HEAD=$(git --git-dir=. rev-parse --verify HEAD) &&
 
 		cd "$LOCAL_REPO" &&
 		git checkout $BRANCH &&
@@ -270,7 +270,7 @@ test_http_push_nonff () {
 		(
 			cd "$REMOTE_REPO" &&
 			echo "$HEAD" >expect &&
-			git rev-parse --verify HEAD >actual &&
+			git --git-dir=. rev-parse --verify HEAD >actual &&
 			test_cmp expect actual
 		)
 	'
@@ -284,18 +284,16 @@ test_http_push_nonff () {
 	'
 
 	test_expect_${EXPECT_CAS_RESULT} 'force with lease aka cas' '
-		HEAD=$(	cd "$REMOTE_REPO" && git rev-parse --verify HEAD ) &&
+		HEAD=$(git --git-dir="$REMOTE_REPO" rev-parse --verify HEAD) &&
 		test_when_finished '\''
-			(cd "$REMOTE_REPO" && git update-ref HEAD "$HEAD")
+			git --git-dir="$REMOTE_REPO" update-ref HEAD "$HEAD"
 		'\'' &&
 		(
 			cd "$LOCAL_REPO" &&
 			git push -v --force-with-lease=$BRANCH:$HEAD origin
 		) &&
 		git rev-parse --verify "$BRANCH" >expect &&
-		(
-			cd "$REMOTE_REPO" && git rev-parse --verify HEAD
-		) >actual &&
+		git --git-dir="$REMOTE_REPO" rev-parse --verify HEAD >actual &&
 		test_cmp expect actual
 	'
 }

t/lib-proto-disable.sh

@@ -17,7 +17,7 @@ test_allow_var () {
 
 	test_expect_success "fetch $desc (enabled)" '
 		(
-			cd tmp.git &&
+			cd tmp.git && GIT_DIR=. && export GIT_DIR &&
 			GIT_ALLOW_PROTOCOL=$proto &&
 			export GIT_ALLOW_PROTOCOL &&
 			git fetch
@@ -26,7 +26,7 @@ test_allow_var () {
 
 	test_expect_success "push $desc (enabled)" '
 		(
-			cd tmp.git &&
+			cd tmp.git && GIT_DIR=. && export GIT_DIR &&
 			GIT_ALLOW_PROTOCOL=$proto &&
 			export GIT_ALLOW_PROTOCOL &&
 			git push origin HEAD:pushed
@@ -35,7 +35,7 @@ test_allow_var () {
 
 	test_expect_success "push $desc (disabled)" '
 		(
-			cd tmp.git &&
+			cd tmp.git && GIT_DIR=. && export GIT_DIR &&
 			GIT_ALLOW_PROTOCOL=none &&
 			export GIT_ALLOW_PROTOCOL &&
 			test_must_fail git push origin HEAD:pushed
@@ -44,7 +44,7 @@ test_allow_var () {
 
 	test_expect_success "fetch $desc (disabled)" '
 		(
-			cd tmp.git &&
+			cd tmp.git && GIT_DIR=. && export GIT_DIR &&
 			GIT_ALLOW_PROTOCOL=none &&
 			export GIT_ALLOW_PROTOCOL &&
 			test_must_fail git fetch
@@ -83,19 +83,19 @@ test_config () {
 	'
 
 	test_expect_success "fetch $desc (enabled)" '
-		git -C tmp.git -c protocol.$proto.allow=always fetch
+		git --git-dir=tmp.git -c protocol.$proto.allow=always fetch
 	'
 
 	test_expect_success "push $desc (enabled)" '
-		git -C tmp.git -c protocol.$proto.allow=always  push origin HEAD:pushed
+		git --git-dir=tmp.git -c protocol.$proto.allow=always  push origin HEAD:pushed
 	'
 
 	test_expect_success "push $desc (disabled)" '
-		test_must_fail git -C tmp.git -c protocol.$proto.allow=never push origin HEAD:pushed
+		test_must_fail git --git-dir=tmp.git -c protocol.$proto.allow=never push origin HEAD:pushed
 	'
 
 	test_expect_success "fetch $desc (disabled)" '
-		test_must_fail git -C tmp.git -c protocol.$proto.allow=never fetch
+		test_must_fail git --git-dir=tmp.git -c protocol.$proto.allow=never fetch
 	'
 
 	test_expect_success "clone $desc (disabled)" '
@@ -110,16 +110,16 @@ test_config () {
 	'
 
 	test_expect_success "fetch $desc (enabled)" '
-		git -C tmp.git -c protocol.$proto.allow=user fetch
+		git --git-dir=tmp.git -c protocol.$proto.allow=user fetch
 	'
 
 	test_expect_success "push $desc (enabled)" '
-		git -C tmp.git -c protocol.$proto.allow=user push origin HEAD:pushed
+		git --git-dir=tmp.git -c protocol.$proto.allow=user push origin HEAD:pushed
 	'
 
 	test_expect_success "push $desc (disabled)" '
 		(
-			cd tmp.git &&
+			cd tmp.git && GIT_DIR=. && export GIT_DIR &&
 			GIT_PROTOCOL_FROM_USER=0 &&
 			export GIT_PROTOCOL_FROM_USER &&
 			test_must_fail git -c protocol.$proto.allow=user push origin HEAD:pushed
@@ -128,7 +128,7 @@ test_config () {
 
 	test_expect_success "fetch $desc (disabled)" '
 		(
-			cd tmp.git &&
+			cd tmp.git && GIT_DIR=. && export GIT_DIR &&
 			GIT_PROTOCOL_FROM_USER=0 &&
 			export GIT_PROTOCOL_FROM_USER &&
 			test_must_fail git -c protocol.$proto.allow=user fetch
@@ -153,22 +153,22 @@ test_config () {
 
 	test_expect_success "fetch $desc (enabled)" '
 		test_config_global protocol.allow always &&
-		git -C tmp.git fetch
+		git --git-dir=tmp.git fetch
 	'
 
 	test_expect_success "push $desc (enabled)" '
 		test_config_global protocol.allow always &&
-		git -C tmp.git push origin HEAD:pushed
+		git --git-dir=tmp.git push origin HEAD:pushed
 	'
 
 	test_expect_success "push $desc (disabled)" '
 		test_config_global protocol.allow never &&
-		test_must_fail git -C tmp.git push origin HEAD:pushed
+		test_must_fail git --git-dir=tmp.git push origin HEAD:pushed
 	'
 
 	test_expect_success "fetch $desc (disabled)" '
 		test_config_global protocol.allow never &&
-		test_must_fail git -C tmp.git fetch
+		test_must_fail git --git-dir=tmp.git fetch
 	'
 
 	test_expect_success "clone $desc (disabled)" '