1 files changed, 45 insertions, 6 deletions

diff --git a/builtin/clone.c b/builtin/clone.c
index 74ec14542e..221edbcdee 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -329,7 +329,20 @@ static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
 	int src_len, dest_len;
 	struct dir_iterator *iter;
 	int iter_status;
-	struct strbuf realpath = STRBUF_INIT;
+
+	/*
+	 * Refuse copying directories by default which aren't owned by us. The
+	 * code that performs either the copying or hardlinking is not prepared
+	 * to handle various edge cases where an adversary may for example
+	 * racily swap out files for symlinks. This can cause us to
+	 * inadvertently use the wrong source file.
+	 *
+	 * Furthermore, even if we were prepared to handle such races safely,
+	 * creating hardlinks across user boundaries is an inherently unsafe
+	 * operation as the hardlinked files can be rewritten at will by the
+	 * potentially-untrusted user. We thus refuse to do so by default.
+	 */
+	die_upon_dubious_ownership(NULL, NULL, src_repo);
 
 	mkdir_if_missing(dest->buf, 0777);
 
@@ -377,9 +390,27 @@ static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
 		if (unlink(dest->buf) && errno != ENOENT)
 			die_errno(_("failed to unlink '%s'"), dest->buf);
 		if (!option_no_hardlinks) {
-			strbuf_realpath(&realpath, src->buf, 1);
-			if (!link(realpath.buf, dest->buf))
+			if (!link(src->buf, dest->buf)) {
+				struct stat st;
+
+				/*
+				 * Sanity-check whether the created hardlink
+				 * actually links to the expected file now. This
+				 * catches time-of-check-time-of-use bugs in
+				 * case the source file was meanwhile swapped.
+				 */
+				if (lstat(dest->buf, &st))
+					die(_("hardlink cannot be checked at '%s'"), dest->buf);
+				if (st.st_mode != iter->st.st_mode ||
+				    st.st_ino != iter->st.st_ino ||
+				    st.st_dev != iter->st.st_dev ||
+				    st.st_size != iter->st.st_size ||
+				    st.st_uid != iter->st.st_uid ||
+				    st.st_gid != iter->st.st_gid)
+					die(_("hardlink different from source at '%s'"), dest->buf);
+
 				continue;
+			}
 			if (option_local > 0)
 				die_errno(_("failed to create link '%s'"), dest->buf);
 			option_no_hardlinks = 1;
@@ -392,8 +423,6 @@ static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
 		strbuf_setlen(src, src_len);
 		die(_("failed to iterate over '%s'"), src->buf);
 	}
-
-	strbuf_release(&realpath);
 }
 
 static void clone_local(const char *src_repo, const char *dest_repo)
@@ -938,6 +967,8 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	int hash_algo;
 	unsigned int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	const int do_not_override_repo_unix_permissions = -1;
+	const char *template_dir;
+	char *template_dir_dup = NULL;
 
 	struct transport_ls_refs_options transport_ls_refs_options =
 		TRANSPORT_LS_REFS_OPTIONS_INIT;
@@ -957,6 +988,13 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 		usage_msg_opt(_("You must specify a repository to clone."),
 			builtin_clone_usage, builtin_clone_options);
 
+	xsetenv("GIT_CLONE_PROTECTION_ACTIVE", "true", 0 /* allow user override */);
+	template_dir = get_template_dir(option_template);
+	if (*template_dir && !is_absolute_path(template_dir))
+		template_dir = template_dir_dup =
+			absolute_pathdup(template_dir);
+	xsetenv("GIT_CLONE_TEMPLATE_DIR", template_dir, 1);
+
 	if (option_depth || option_since || option_not.nr)
 		deepen = 1;
 	if (option_single_branch == -1)
@@ -1118,7 +1156,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * repository, and reference backends may persist that information into
 	 * their on-disk data structures.
 	 */
-	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
+	init_db(git_dir, real_git_dir, template_dir, GIT_HASH_UNKNOWN,
 		ref_storage_format, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
@@ -1507,6 +1545,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	free(dir);
 	free(path);
 	free(repo_to_free);
+	free(template_dir_dup);
 	junk_mode = JUNK_LEAVE_ALL;
 
 	transport_ls_refs_options_release(&transport_ls_refs_options);