scalar: avoid segfault in reconfigure --all

During the latest v2.45.0 update, 'scalar reconfigure --all' started to
segfault on my machine. Breaking it down via the debugger, it was
faulting on a NULL reference to the_hash_algo, which is a macro pointing
to the_repository->hash_algo.

In my case, this is due to one of my repositories having a detached HEAD,
which requires get_oid_hex() to parse that the HEAD reference is valid.
Another way to cause a failure is to use the "includeIf.onbranch" config
key, which will lead to a BUG() statement.

My first inclination was to try to refactor cmd_reconfigure() to execute
'git for-each-repo' instead of this loop. In addition to the difficulty
of executing 'scalar reconfigure' within 'git for-each-repo', it would
be difficult to perform the clean-up logic for non-existent repos if we
relied on that child process.

Instead, I chose to move the temporary repo to be within the loop and
reinstate the_repository to its old value after we are done performing
logic on the current array item.

Add tests to t9210-scalar.sh to test 'scalar reconfigure --all' with
multiple registered repos. There are two different ways that the old
use of the_repository could trigger bugs. These issues are being solved
independently to be more careful about the_repository being
uninitialized, but the change in this patch around the use of
the_repository is still a good safety precaution.

Co-authored-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/scalar.c b/scalar.c
index fb2940c2a0..7234049a1b 100644
--- a/scalar.c
+++ b/scalar.c
@@ -645,7 +645,6 @@ static int cmd_reconfigure(int argc, const char **argv)
 	};
 	struct string_list scalar_repos = STRING_LIST_INIT_DUP;
 	int i, res = 0;
-	struct repository r = { NULL };
 	struct strbuf commondir = STRBUF_INIT, gitdir = STRBUF_INIT;
 
 	argc = parse_options(argc, argv, NULL, options,
@@ -665,6 +664,7 @@ static int cmd_reconfigure(int argc, const char **argv)
 
 	for (i = 0; i < scalar_repos.nr; i++) {
 		int succeeded = 0;
+		struct repository *old_repo, r = { NULL };
 		const char *dir = scalar_repos.items[i].string;
 
 		strbuf_reset(&commondir);
@@ -712,13 +712,17 @@ static int cmd_reconfigure(int argc, const char **argv)
 
 		git_config_clear();
 
+		if (repo_init(&r, gitdir.buf, commondir.buf))
+			goto loop_end;
+
+		old_repo = the_repository;
 		the_repository = &r;
-		r.commondir = commondir.buf;
-		r.gitdir = gitdir.buf;
 
 		if (set_recommended_config(1) >= 0)
 			succeeded = 1;
 
+		the_repository = old_repo;
+
 loop_end:
 		if (!succeeded) {
 			res = -1;