checkout: fix "branch info" memory leaks

The "checkout" command is one of the main sources of leaks in the test
suite, let's fix the common ones by not leaking from the "struct
branch_info".

Doing this is rather straightforward, albeit verbose, we need to
xstrdup() constant strings going into the struct, and free() the ones
we clobber as we go along.

This also means that we can delete previous partial leak fixes in this
area, i.e. the "path_to_free" accounting added by 96ec7b1e708 (Convert
resolve_ref+xstrdup to new resolve_refdup function, 2011-12-13).

There was some discussion about whether "we should retain the "const
char *" here and cast at free() time, or have it be a "char *". Since
this is not a public API with any sort of API boundary let's use
"char *", as is already being done for the "refname" member of the
same struct.

The tests to mark as passing were found with:

    rm .prove; GIT_SKIP_TESTS=t0027 prove -j8 --state=save t[0-9]*.sh :: --immediate
    # apply & compile this change
    prove -j8 --state=failed :: --immediate

I.e. the ones that were newly passing when the --state=failed command
was run. I left out "t3040-subprojects-basic.sh" and
"t4131-apply-fake-ancestor.sh" to to optimization-level related
differences similar to the ones noted in[1], except that these would
be something the current 'linux-leaks' job would run into.

1. https://lore.kernel.org/git/cover-v3-0.6-00000000000-20211022T175227Z-avarab@gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 55 insertions, 31 deletions

diff --git a/builtin/checkout.c b/builtin/checkout.c
index cbf73b8c9f6..43d0275187f 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -91,8 +91,8 @@ struct checkout_opts {
 };
 
 struct branch_info {
-	const char *name; /* The short name used */
-	const char *path; /* The full name of a real branch */
+	char *name; /* The short name used */
+	char *path; /* The full name of a real branch */
 	struct commit *commit; /* The named commit */
 	char *refname; /* The full name of the ref being checked out. */
 	struct object_id oid; /* The object ID of the commit being checked out. */
@@ -103,6 +103,14 @@ struct branch_info {
 	char *checkout;
 };
 
+static void branch_info_release(struct branch_info *info)
+{
+	free(info->name);
+	free(info->path);
+	free(info->refname);
+	free(info->checkout);
+}
+
 static int post_checkout_hook(struct commit *old_commit, struct commit *new_commit,
 			      int changed)
 {
@@ -688,9 +696,12 @@ static void setup_branch_path(struct branch_info *branch)
 		repo_get_oid_committish(the_repository, branch->name, &branch->oid);
 
 	strbuf_branchname(&buf, branch->name, INTERPRET_BRANCH_LOCAL);
-	if (strcmp(buf.buf, branch->name))
+	if (strcmp(buf.buf, branch->name)) {
+		free(branch->name);
 		branch->name = xstrdup(buf.buf);
+	}
 	strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
+	free(branch->path);
 	branch->path = strbuf_detach(&buf, NULL);
 }
 
@@ -894,7 +905,9 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 				      opts->new_branch_log,
 				      opts->quiet,
 				      opts->track);
-		new_branch_info->name = opts->new_branch;
+		free(new_branch_info->name);
+		free(new_branch_info->refname);
+		new_branch_info->name = xstrdup(opts->new_branch);
 		setup_branch_path(new_branch_info);
 	}
 
@@ -1062,8 +1075,7 @@ static int switch_branches(const struct checkout_opts *opts,
 			   struct branch_info *new_branch_info)
 {
 	int ret = 0;
-	struct branch_info old_branch_info;
-	void *path_to_free;
+	struct branch_info old_branch_info = { 0 };
 	struct object_id rev;
 	int flag, writeout_error = 0;
 	int do_merge = 1;
@@ -1071,25 +1083,32 @@ static int switch_branches(const struct checkout_opts *opts,
 	trace2_cmd_mode("branch");
 
 	memset(&old_branch_info, 0, sizeof(old_branch_info));
-	old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
+	old_branch_info.path = resolve_refdup("HEAD", 0, &rev, &flag);
 	if (old_branch_info.path)
 		old_branch_info.commit = lookup_commit_reference_gently(the_repository, &rev, 1);
 	if (!(flag & REF_ISSYMREF))
-		old_branch_info.path = NULL;
+		FREE_AND_NULL(old_branch_info.path);
 
-	if (old_branch_info.path)
-		skip_prefix(old_branch_info.path, "refs/heads/", &old_branch_info.name);
+	if (old_branch_info.path) {
+		const char *const prefix = "refs/heads/";
+		const char *p;
+		if (skip_prefix(old_branch_info.path, prefix, &p))
+			old_branch_info.name = xstrdup(p);
+		else
+			BUG("should be able to skip past '%s' in '%s'!",
+			    prefix, old_branch_info.path);
+	}
 
 	if (opts->new_orphan_branch && opts->orphan_from_empty_tree) {
 		if (new_branch_info->name)
 			BUG("'switch --orphan' should never accept a commit as starting point");
 		new_branch_info->commit = NULL;
-		new_branch_info->name = "(empty)";
+		new_branch_info->name = xstrdup("(empty)");
 		do_merge = 1;
 	}
 
 	if (!new_branch_info->name) {
-		new_branch_info->name = "HEAD";
+		new_branch_info->name = xstrdup("HEAD");
 		new_branch_info->commit = old_branch_info.commit;
 		if (!new_branch_info->commit)
 			die(_("You are on a branch yet to be born"));
@@ -1102,7 +1121,7 @@ static int switch_branches(const struct checkout_opts *opts,
 	if (do_merge) {
 		ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
 		if (ret) {
-			free(path_to_free);
+			branch_info_release(&old_branch_info);
 			return ret;
 		}
 	}
@@ -1113,7 +1132,8 @@ static int switch_branches(const struct checkout_opts *opts,
 	update_refs_for_switch(opts, &old_branch_info, new_branch_info);
 
 	ret = post_checkout_hook(old_branch_info.commit, new_branch_info->commit, 1);
-	free(path_to_free);
+	branch_info_release(&old_branch_info);
+
 	return ret || writeout_error;
 }
 
@@ -1145,16 +1165,15 @@ static void setup_new_branch_info_and_source_tree(
 	struct tree **source_tree = &opts->source_tree;
 	struct object_id branch_rev;
 
-	new_branch_info->name = arg;
+	new_branch_info->name = xstrdup(arg);
 	setup_branch_path(new_branch_info);
 
 	if (!check_refname_format(new_branch_info->path, 0) &&
 	    !read_ref(new_branch_info->path, &branch_rev))
 		oidcpy(rev, &branch_rev);
-	else {
-		free((char *)new_branch_info->path);
-		new_branch_info->path = NULL; /* not an existing branch */
-	}
+	else
+		/* not an existing branch */
+		FREE_AND_NULL(new_branch_info->path);
 
 	new_branch_info->commit = lookup_commit_reference_gently(the_repository, rev, 1);
 	if (!new_branch_info->commit) {
@@ -1574,12 +1593,11 @@ static char cb_option = 'b';
 
 static int checkout_main(int argc, const char **argv, const char *prefix,
 			 struct checkout_opts *opts, struct option *options,
-			 const char * const usagestr[])
+			 const char * const usagestr[],
+			 struct branch_info *new_branch_info)
 {
-	struct branch_info new_branch_info;
 	int parseopt_flags = 0;
 
-	memset(&new_branch_info, 0, sizeof(new_branch_info));
 	opts->overwrite_ignore = 1;
 	opts->prefix = prefix;
 	opts->show_progress = -1;
@@ -1688,7 +1706,7 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 			opts->track == BRANCH_TRACK_UNSPECIFIED &&
 			!opts->new_branch;
 		int n = parse_branchname_arg(argc, argv, dwim_ok,
-					     &new_branch_info, opts, &rev);
+					     new_branch_info, opts, &rev);
 		argv += n;
 		argc -= n;
 	} else if (!opts->accept_ref && opts->from_treeish) {
@@ -1697,7 +1715,7 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 		if (get_oid_mb(opts->from_treeish, &rev))
 			die(_("could not resolve %s"), opts->from_treeish);
 
-		setup_new_branch_info_and_source_tree(&new_branch_info,
+		setup_new_branch_info_and_source_tree(new_branch_info,
 						      opts, &rev,
 						      opts->from_treeish);
 
@@ -1717,7 +1735,7 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 		 * Try to give more helpful suggestion.
 		 * new_branch && argc > 1 will be caught later.
 		 */
-		if (opts->new_branch && argc == 1 && !new_branch_info.commit)
+		if (opts->new_branch && argc == 1 && !new_branch_info->commit)
 			die(_("'%s' is not a commit and a branch '%s' cannot be created from it"),
 				argv[0], opts->new_branch);
 
@@ -1766,11 +1784,10 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 		strbuf_release(&buf);
 	}
 
-	UNLEAK(opts);
 	if (opts->patch_mode || opts->pathspec.nr)
-		return checkout_paths(opts, &new_branch_info);
+		return checkout_paths(opts, new_branch_info);
 	else
-		return checkout_branch(opts, &new_branch_info);
+		return checkout_branch(opts, new_branch_info);
 }
 
 int cmd_checkout(int argc, const char **argv, const char *prefix)
@@ -1789,6 +1806,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 	int ret;
+	struct branch_info new_branch_info = { 0 };
 
 	memset(&opts, 0, sizeof(opts));
 	opts.dwim_new_local_branch = 1;
@@ -1819,7 +1837,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	options = add_checkout_path_options(&opts, options);
 
 	ret = checkout_main(argc, argv, prefix, &opts,
-			    options, checkout_usage);
+			    options, checkout_usage, &new_branch_info);
+	branch_info_release(&new_branch_info);
+	clear_pathspec(&opts.pathspec);
 	FREE_AND_NULL(options);
 	return ret;
 }
@@ -1840,6 +1860,7 @@ int cmd_switch(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 	int ret;
+	struct branch_info new_branch_info = { 0 };
 
 	memset(&opts, 0, sizeof(opts));
 	opts.dwim_new_local_branch = 1;
@@ -1859,7 +1880,8 @@ int cmd_switch(int argc, const char **argv, const char *prefix)
 	cb_option = 'c';
 
 	ret = checkout_main(argc, argv, prefix, &opts,
-			    options, switch_branch_usage);
+			    options, switch_branch_usage, &new_branch_info);
+	branch_info_release(&new_branch_info);
 	FREE_AND_NULL(options);
 	return ret;
 }
@@ -1881,6 +1903,7 @@ int cmd_restore(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 	int ret;
+	struct branch_info new_branch_info = { 0 };
 
 	memset(&opts, 0, sizeof(opts));
 	opts.accept_ref = 0;
@@ -1896,7 +1919,8 @@ int cmd_restore(int argc, const char **argv, const char *prefix)
 	options = add_checkout_path_options(&opts, options);
 
 	ret = checkout_main(argc, argv, prefix, &opts,
-			    options, restore_usage);
+			    options, restore_usage, &new_branch_info);
+	branch_info_release(&new_branch_info);
 	FREE_AND_NULL(options);
 	return ret;
 }