Copy resolve_ref() return value for longer use

resolve_ref() may return a pointer to a static buffer. Callers that
use this value longer than a couple of statements should copy the
value to avoid some hidden resolve_ref() call that may change the
static buffer's value.

The bug found by Tony Wang <wwwjfy@gmail.com> in builtin/merge.c
demonstrates this. The first call is in cmd_merge()

branch = resolve_ref("HEAD", head_sha1, 0, &flag);

Then deep in lookup_commit_or_die() a few lines after, resolve_ref()
may be called again and destroy "branch".

lookup_commit_or_die
 lookup_commit_reference
  lookup_commit_reference_gently
   parse_object
    lookup_replace_object
     do_lookup_replace_object
      prepare_replace_object
       for_each_replace_ref
        do_for_each_ref
         get_loose_refs
          get_ref_dir
           get_ref_dir
            resolve_ref

All call sites are checked and made sure that xstrdup() is called if
the value should be saved.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -115,8 +115,10 @@ static int branch_merged(int kind, const char *name,
 		    branch->merge[0] &&
 		    branch->merge[0]->dst &&
 		    (reference_name =
-		     resolve_ref(branch->merge[0]->dst, sha1, 1, NULL)) != NULL)
+		     resolve_ref(branch->merge[0]->dst, sha1, 1, NULL)) != NULL) {
+			reference_name = xstrdup(reference_name);
 			reference_rev = lookup_commit_reference(sha1);
+		}
 	}
 	if (!reference_rev)
 		reference_rev = head_rev;
@@ -141,6 +143,7 @@ static int branch_merged(int kind, const char *name,
 				"         '%s', even though it is merged to HEAD."),
 				name, reference_name);
 	}
+	free((char *)reference_name);
 	return merged;
 }
 

builtin/checkout.c

@@ -699,7 +699,9 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
 	unsigned char rev[20];
 	int flag;
 	memset(&old, 0, sizeof(old));
-	old.path = xstrdup(resolve_ref("HEAD", rev, 0, &flag));
+	old.path = resolve_ref("HEAD", rev, 0, &flag);
+	if (old.path)
+		old.path = xstrdup(old.path);
 	old.commit = lookup_commit_reference_gently(rev, 1);
 	if (!(flag & REF_ISSYMREF)) {
 		free((char *)old.path);

builtin/commit.c

@@ -1259,7 +1259,7 @@ static void print_summary(const char *prefix, const unsigned char *sha1,
 	struct commit *commit;
 	struct strbuf format = STRBUF_INIT;
 	unsigned char junk_sha1[20];
-	const char *head = resolve_ref("HEAD", junk_sha1, 0, NULL);
+	const char *head;
 	struct pretty_print_context pctx = {0};
 	struct strbuf author_ident = STRBUF_INIT;
 	struct strbuf committer_ident = STRBUF_INIT;
@@ -1304,6 +1304,7 @@ static void print_summary(const char *prefix, const unsigned char *sha1,
 	rev.diffopt.break_opt = 0;
 	diff_setup_done(&rev.diffopt);
 
+	head = resolve_ref("HEAD", junk_sha1, 0, NULL);
 	printf("[%s%s ",
 		!prefixcmp(head, "refs/heads/") ?
 			head + 11 :

builtin/fmt-merge-msg.c

@@ -268,6 +268,7 @@ static int do_fmt_merge_msg(int merge_title, struct strbuf *in,
 		die("No current branch");
 	if (!prefixcmp(current_branch, "refs/heads/"))
 		current_branch += 11;
+	current_branch = xstrdup(current_branch);
 
 	/* get a line */
 	while (pos < in->len) {
@@ -283,8 +284,10 @@ static int do_fmt_merge_msg(int merge_title, struct strbuf *in,
 			die ("Error in line %d: %.*s", i, len, p);
 	}
 
-	if (!srcs.nr)
+	if (!srcs.nr) {
+		free((char*)current_branch);
 		return 0;
+	}
 
 	if (merge_title)
 		do_fmt_merge_msg_title(out, current_branch);
@@ -306,6 +309,7 @@ static int do_fmt_merge_msg(int merge_title, struct strbuf *in,
 			shortlog(origins.items[i].string, origins.items[i].util,
 					head, &rev, shortlog_len, out);
 	}
+	free((char *)current_branch);
 	return 0;
 }
 

builtin/merge.c

@@ -1082,7 +1082,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	struct commit *head_commit;
 	struct strbuf buf = STRBUF_INIT;
 	const char *head_arg;
-	int flag, i;
+	int flag, i, ret = 0;
 	int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
 	struct commit_list *common = NULL;
 	const char *best_strategy = NULL, *wt_strategy = NULL;
@@ -1096,8 +1096,11 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	 * current branch.
 	 */
 	branch = resolve_ref("HEAD", head_sha1, 0, &flag);
-	if (branch && !prefixcmp(branch, "refs/heads/"))
-		branch += 11;
+	if (branch) {
+		if (!prefixcmp(branch, "refs/heads/"))
+			branch += 11;
+		branch = xstrdup(branch);
+	}
 	if (!branch || is_null_sha1(head_sha1))
 		head_commit = NULL;
 	else
@@ -1121,7 +1124,8 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 			die(_("There is no merge to abort (MERGE_HEAD missing)."));
 
 		/* Invoke 'git reset --merge' */
-		return cmd_reset(nargc, nargv, prefix);
+		ret = cmd_reset(nargc, nargv, prefix);
+		goto done;
 	}
 
 	if (read_cache_unmerged())
@@ -1205,7 +1209,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		read_empty(remote_head->sha1, 0);
 		update_ref("initial pull", "HEAD", remote_head->sha1, NULL, 0,
 				DIE_ON_ERR);
-		return 0;
+		goto done;
 	} else {
 		struct strbuf merge_names = STRBUF_INIT;
 
@@ -1292,7 +1296,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		 * but first the most common case of merging one remote.
 		 */
 		finish_up_to_date("Already up-to-date.");
-		return 0;
+		goto done;
 	} else if (allow_fast_forward && !remoteheads->next &&
 			!common->next &&
 			!hashcmp(common->item->object.sha1, head_commit->object.sha1)) {
@@ -1313,15 +1317,20 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 			strbuf_addstr(&msg,
 				" (no commit created; -m option ignored)");
 		o = want_commit(sha1_to_hex(remoteheads->item->object.sha1));
-		if (!o)
-			return 1;
+		if (!o) {
+			ret = 1;
+			goto done;
+		}
 
-		if (checkout_fast_forward(head_commit->object.sha1, remoteheads->item->object.sha1))
-			return 1;
+		if (checkout_fast_forward(head_commit->object.sha1,
+					  remoteheads->item->object.sha1)) {
+			ret = 1;
+			goto done;
+		}
 
 		finish(head_commit, o->sha1, msg.buf);
 		drop_save();
-		return 0;
+		goto done;
 	} else if (!remoteheads->next && common->next)
 		;
 		/*
@@ -1339,8 +1348,11 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 			git_committer_info(IDENT_ERROR_ON_NO_NAME);
 			printf(_("Trying really trivial in-index merge...\n"));
 			if (!read_tree_trivial(common->item->object.sha1,
-					head_commit->object.sha1, remoteheads->item->object.sha1))
-				return merge_trivial(head_commit);
+					       head_commit->object.sha1,
+					       remoteheads->item->object.sha1)) {
+				ret = merge_trivial(head_commit);
+				goto done;
+			}
 			printf(_("Nope.\n"));
 		}
 	} else {
@@ -1368,7 +1380,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		}
 		if (up_to_date) {
 			finish_up_to_date("Already up-to-date. Yeeah!");
-			return 0;
+			goto done;
 		}
 	}
 
@@ -1450,9 +1462,11 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	 * If we have a resulting tree, that means the strategy module
 	 * auto resolved the merge cleanly.
 	 */
-	if (automerge_was_ok)
-		return finish_automerge(head_commit, common, result_tree,
-					wt_strategy);
+	if (automerge_was_ok) {
+		ret = finish_automerge(head_commit, common, result_tree,
+				       wt_strategy);
+		goto done;
+	}
 
 	/*
 	 * Pick the result from the best strategy and have the user fix
@@ -1466,7 +1480,8 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		else
 			fprintf(stderr, _("Merge with strategy %s failed.\n"),
 				use_strategies[0]->name);
-		return 2;
+		ret = 2;
+		goto done;
 	} else if (best_strategy == wt_strategy)
 		; /* We already have its result in the working tree. */
 	else {
@@ -1482,10 +1497,13 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	else
 		write_merge_state();
 
-	if (merge_was_ok) {
+	if (merge_was_ok)
 		fprintf(stderr, _("Automatic merge went well; "
 			"stopped before committing as requested\n"));
-		return 0;
-	} else
-		return suggest_conflicts(option_renormalize);
+	else
+		ret = suggest_conflicts(option_renormalize);
+
+done:
+	free((char *)branch);
+	return ret;
 }

builtin/notes.c

@@ -804,6 +804,7 @@ static int merge_commit(struct notes_merge_options *o)
 	struct notes_tree *t;
 	struct commit *partial;
 	struct pretty_print_context pretty_ctx;
+	int ret;
 
 	/*
 	 * Read partial merge result from .git/NOTES_MERGE_PARTIAL,
@@ -828,6 +829,7 @@ static int merge_commit(struct notes_merge_options *o)
 	o->local_ref = resolve_ref("NOTES_MERGE_REF", sha1, 0, NULL);
 	if (!o->local_ref)
 		die("Failed to resolve NOTES_MERGE_REF");
+	o->local_ref = xstrdup(o->local_ref);
 
 	if (notes_merge_commit(o, t, partial, sha1))
 		die("Failed to finalize notes merge");
@@ -843,7 +845,9 @@ static int merge_commit(struct notes_merge_options *o)
 
 	free_notes(t);
 	strbuf_release(&msg);
-	return merge_abort(o);
+	ret = merge_abort(o);
+	free((char *)o->local_ref);
+	return ret;
 }
 
 static int merge(int argc, const char **argv, const char *prefix)

builtin/receive-pack.c

@@ -695,7 +695,10 @@ static void execute_commands(struct command *commands, const char *unpacker_erro
 
 	check_aliased_updates(commands);
 
+	free((char *)head_name);
 	head_name = resolve_ref("HEAD", sha1, 0, NULL);
+	if (head_name)
+		head_name = xstrdup(head_name);
 
 	for (cmd = commands; cmd; cmd = cmd->next)
 		if (!cmd->skip_update)

reflog-walk.c

@@ -51,8 +51,11 @@ static struct complete_reflogs *read_complete_reflog(const char *ref)
 	if (reflogs->nr == 0) {
 		unsigned char sha1[20];
 		const char *name = resolve_ref(ref, sha1, 1, NULL);
-		if (name)
+		if (name) {
+			name = xstrdup(name);
 			for_each_reflog_ent(name, read_one_reflog, reflogs);
+			free((char *)name);
+		}
 	}
 	if (reflogs->nr == 0) {
 		int len = strlen(ref);