[PATCH v3 1/2] worktree: do not pass strbuf by value

[Deveshi Dwivedi <deveshigurgaon@gmail.com>]

write_worktree_linking_files() takes two struct strbuf parameters by
value, even though it only reads path strings from them.

Passing a strbuf by value is misleading and dangerous. The structure
carries a pointer to its underlying character array; caller and callee
end up sharing that storage.  If the callee ever causes the strbuf to
be reallocated, the caller's copy becomes a dangling pointer, which
results in a double-free when the caller does strbuf_release().

The function only needs the string values, not the strbuf machinery.
Switch it to take const char * and update all callers to pass .buf.

Signed-off-by: Deveshi Dwivedi <deveshigurgaon@gmail.com>
---
 builtin/worktree.c |  2 +-
 worktree.c         | 22 +++++++++++-----------
 worktree.h         |  2 +-
 3 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/builtin/worktree.c b/builtin/worktree.c
index bc2d0d645b..4035b1cb06 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -539,7 +539,7 @@ static int add_worktree(const char *path, const char *refname,
 
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/gitdir", sb_repo.buf);
-	write_worktree_linking_files(sb_git, sb, opts->relative_paths);
+	write_worktree_linking_files(sb_git.buf, sb.buf, opts->relative_paths);
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/commondir", sb_repo.buf);
 	write_file(sb.buf, "../..");
diff --git a/worktree.c b/worktree.c
index 6e2f0f7828..7eba12c6ed 100644
--- a/worktree.c
+++ b/worktree.c
@@ -445,7 +445,7 @@ void update_worktree_location(struct worktree *wt, const char *path_,
 	strbuf_realpath(&path, path_, 1);
 	strbuf_addf(&dotgit, "%s/.git", path.buf);
 	if (fspathcmp(wt->path, path.buf)) {
-		write_worktree_linking_files(dotgit, gitdir, use_relative_paths);
+		write_worktree_linking_files(dotgit.buf, gitdir.buf, use_relative_paths);
 
 		free(wt->path);
 		wt->path = strbuf_detach(&path, NULL);
@@ -684,7 +684,7 @@ static void repair_gitfile(struct worktree *wt,
 
 	if (repair) {
 		fn(0, wt->path, repair, cb_data);
-		write_worktree_linking_files(dotgit, gitdir, use_relative_paths);
+		write_worktree_linking_files(dotgit.buf, gitdir.buf, use_relative_paths);
 	}
 
 done:
@@ -742,7 +742,7 @@ void repair_worktree_after_gitdir_move(struct worktree *wt, const char *old_path
 	if (!file_exists(dotgit.buf))
 		goto done;
 
-	write_worktree_linking_files(dotgit, gitdir, is_relative_path);
+	write_worktree_linking_files(dotgit.buf, gitdir.buf, is_relative_path);
 done:
 	strbuf_release(&gitdir);
 	strbuf_release(&dotgit);
@@ -913,7 +913,7 @@ void repair_worktree_at_path(const char *path,
 
 	if (repair) {
 		fn(0, gitdir.buf, repair, cb_data);
-		write_worktree_linking_files(dotgit, gitdir, use_relative_paths);
+		write_worktree_linking_files(dotgit.buf, gitdir.buf, use_relative_paths);
 	}
 done:
 	free(dotgit_contents);
@@ -1087,17 +1087,17 @@ int init_worktree_config(struct repository *r)
 	return res;
 }
 
-void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
+void write_worktree_linking_files(const char *dotgit, const char *gitdir,
 				  int use_relative_paths)
 {
 	struct strbuf path = STRBUF_INIT;
 	struct strbuf repo = STRBUF_INIT;
 	struct strbuf tmp = STRBUF_INIT;
 
-	strbuf_addbuf(&path, &dotgit);
+	strbuf_addstr(&path, dotgit);
 	strbuf_strip_suffix(&path, "/.git");
 	strbuf_realpath(&path, path.buf, 1);
-	strbuf_addbuf(&repo, &gitdir);
+	strbuf_addstr(&repo, gitdir);
 	strbuf_strip_suffix(&repo, "/gitdir");
 	strbuf_realpath(&repo, repo.buf, 1);
 
@@ -1110,11 +1110,11 @@ void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
 	}
 
 	if (use_relative_paths) {
-		write_file(gitdir.buf, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
-		write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
+		write_file(gitdir, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
+		write_file(dotgit, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
 	} else {
-		write_file(gitdir.buf, "%s/.git", path.buf);
-		write_file(dotgit.buf, "gitdir: %s", repo.buf);
+		write_file(gitdir, "%s/.git", path.buf);
+		write_file(dotgit, "gitdir: %s", repo.buf);
 	}
 
 	strbuf_release(&path);
diff --git a/worktree.h b/worktree.h
index 06efe26b83..f4e46be385 100644
--- a/worktree.h
+++ b/worktree.h
@@ -240,7 +240,7 @@ int init_worktree_config(struct repository *r);
  *  dotgit: "/path/to/foo/.git"
  *  gitdir: "/path/to/repo/worktrees/foo/gitdir"
  */
-void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
+void write_worktree_linking_files(const char *dotgit, const char *gitdir,
 				  int use_relative_paths);
 
 #endif
-- 
2.52.0.230.gd8af7cadaa