Always check parse_tree*()'s return value

Otherwise we may easily run into serious crashes: For example, if we run
`init_tree_desc()` directly after a failed `parse_tree()`, we are
accessing uninitialized data or trying to dereference `NULL`.

Note that the `parse_tree()` function already takes care of showing an
error message. The `parse_tree_indirectly()` and
`repo_get_commit_tree()` functions do not, therefore those latter call
sites need to show a useful error message while the former do not.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

builtin/checkout.c

@@ -707,7 +707,8 @@ static int reset_tree(struct tree *tree, const struct checkout_opts *o,
 	init_checkout_metadata(&opts.meta, info->refname,
 			       info->commit ? &info->commit->object.oid : null_oid(),
 			       NULL);
-	parse_tree(tree);
+	if (parse_tree(tree) < 0)
+		return 128;
 	init_tree_desc(&tree_desc, tree->buffer, tree->size);
 	switch (unpack_trees(1, &tree_desc, &opts)) {
 	case -2:
@@ -786,9 +787,15 @@ static int merge_working_tree(const struct checkout_opts *opts,
 		if (new_branch_info->commit)
 			BUG("'switch --orphan' should never accept a commit as starting point");
 		new_tree = parse_tree_indirect(the_hash_algo->empty_tree);
-	} else
+		if (!new_tree)
+			BUG("unable to read empty tree");
+	} else {
 		new_tree = repo_get_commit_tree(the_repository,
 						new_branch_info->commit);
+		if (!new_tree)
+			return error(_("unable to read tree %s"),
+				     oid_to_hex(&new_branch_info->commit->object.oid));
+	}
 	if (opts->discard_changes) {
 		ret = reset_tree(new_tree, opts, 1, writeout_error, new_branch_info);
 		if (ret)
@@ -823,7 +830,8 @@ static int merge_working_tree(const struct checkout_opts *opts,
 				oid_to_hex(old_commit_oid));
 
 		init_tree_desc(&trees[0], tree->buffer, tree->size);
-		parse_tree(new_tree);
+		if (parse_tree(new_tree) < 0)
+			exit(128);
 		tree = new_tree;
 		init_tree_desc(&trees[1], tree->buffer, tree->size);
 
@@ -1239,10 +1247,15 @@ static void setup_new_branch_info_and_source_tree(
 	if (!new_branch_info->commit) {
 		/* not a commit */
 		*source_tree = parse_tree_indirect(rev);
+		if (!*source_tree)
+			die(_("unable to read tree %s"), oid_to_hex(rev));
 	} else {
 		parse_commit_or_die(new_branch_info->commit);
 		*source_tree = repo_get_commit_tree(the_repository,
 						    new_branch_info->commit);
+		if (!*source_tree)
+			die(_("unable to read tree %s"),
+			    oid_to_hex(&new_branch_info->commit->object.oid));
 	}
 }
 

builtin/clone.c

@@ -736,7 +736,8 @@ static int checkout(int submodule_progress, int filter_submodules)
 	tree = parse_tree_indirect(&oid);
 	if (!tree)
 		die(_("unable to parse commit %s"), oid_to_hex(&oid));
-	parse_tree(tree);
+	if (parse_tree(tree) < 0)
+		exit(128);
 	init_tree_desc(&t, tree->buffer, tree->size);
 	if (unpack_trees(1, &t, &opts) < 0)
 		die(_("unable to checkout working tree"));

builtin/commit.c

@@ -339,7 +339,8 @@ static void create_base_index(const struct commit *current_head)
 	tree = parse_tree_indirect(&current_head->object.oid);
 	if (!tree)
 		die(_("failed to unpack HEAD tree object"));
-	parse_tree(tree);
+	if (parse_tree(tree) < 0)
+		exit(128);
 	init_tree_desc(&t, tree->buffer, tree->size);
 	if (unpack_trees(1, &t, &opts))
 		exit(128); /* We've already reported the error, finish dying */

builtin/merge-tree.c

@@ -447,12 +447,18 @@ static int real_merge(struct merge_tree_options *o,
 		if (repo_get_oid_treeish(the_repository, merge_base, &base_oid))
 			die(_("could not parse as tree '%s'"), merge_base);
 		base_tree = parse_tree_indirect(&base_oid);
+		if (!base_tree)
+			die(_("unable to read tree %s"), oid_to_hex(&base_oid));
 		if (repo_get_oid_treeish(the_repository, branch1, &head_oid))
 			die(_("could not parse as tree '%s'"), branch1);
 		parent1_tree = parse_tree_indirect(&head_oid);
+		if (!parent1_tree)
+			die(_("unable to read tree %s"), oid_to_hex(&head_oid));
 		if (repo_get_oid_treeish(the_repository, branch2, &merge_oid))
 			die(_("could not parse as tree '%s'"), branch2);
 		parent2_tree = parse_tree_indirect(&merge_oid);
+		if (!parent2_tree)
+			die(_("unable to read tree %s"), oid_to_hex(&merge_oid));
 
 		opt.ancestor = merge_base;
 		merge_incore_nonrecursive(&opt, base_tree, parent1_tree, parent2_tree, &result);

builtin/read-tree.c

@@ -263,7 +263,8 @@ int cmd_read_tree(int argc, const char **argv, const char *cmd_prefix)
 	cache_tree_free(&the_index.cache_tree);
 	for (i = 0; i < nr_trees; i++) {
 		struct tree *tree = trees[i];
-		parse_tree(tree);
+		if (parse_tree(tree) < 0)
+			return 128;
 		init_tree_desc(t+i, tree->buffer, tree->size);
 	}
 	if (unpack_trees(nr_trees, t, &opts))

builtin/reset.c

@@ -119,6 +119,10 @@ static int reset_index(const char *ref, const struct object_id *oid, int reset_t
 
 	if (reset_type == MIXED || reset_type == HARD) {
 		tree = parse_tree_indirect(oid);
+		if (!tree) {
+			error(_("unable to read tree %s"), oid_to_hex(oid));
+			goto out;
+		}
 		prime_cache_tree(the_repository, the_repository->index, tree);
 	}
 

cache-tree.c

@@ -779,8 +779,8 @@ static void prime_cache_tree_rec(struct repository *r,
 			struct cache_tree_sub *sub;
 			struct tree *subtree = lookup_tree(r, &entry.oid);
 
-			if (!subtree->object.parsed)
-				parse_tree(subtree);
+			if (!subtree->object.parsed && parse_tree(subtree) < 0)
+				exit(128);
 			sub = cache_tree_sub(it, entry.path);
 			sub->cache_tree = cache_tree();
 

merge-ort.c

@@ -4983,6 +4983,9 @@ static void merge_ort_nonrecursive_internal(struct merge_options *opt,
 
 	if (result->clean >= 0) {
 		result->tree = parse_tree_indirect(&working_tree_oid);
+		if (!result->tree)
+			die(_("unable to read tree %s"),
+			    oid_to_hex(&working_tree_oid));
 		/* existence of conflicted entries implies unclean */
 		result->clean &= strmap_empty(&opt->priv->conflicted);
 	}

merge-recursive.c

@@ -410,7 +410,8 @@ static inline int merge_detect_rename(struct merge_options *opt)
 
 static void init_tree_desc_from_tree(struct tree_desc *desc, struct tree *tree)
 {
-	parse_tree(tree);
+	if (parse_tree(tree) < 0)
+		exit(128);
 	init_tree_desc(desc, tree->buffer, tree->size);
 }
 

merge.c

@@ -80,7 +80,10 @@ int checkout_fast_forward(struct repository *r,
 		return -1;
 	}
 	for (i = 0; i < nr_trees; i++) {
-		parse_tree(trees[i]);
+		if (parse_tree(trees[i]) < 0) {
+			rollback_lock_file(&lock_file);
+			return -1;
+		}
 		init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
 	}
 

reset.c

@@ -158,6 +158,11 @@ int reset_head(struct repository *r, const struct reset_head_opts *opts)
 	}
 
 	tree = parse_tree_indirect(oid);
+	if (!tree) {
+		ret = error(_("unable to read tree %s"), oid_to_hex(oid));
+		goto leave_reset_head;
+	}
+
 	prime_cache_tree(r, r->index, tree);
 
 	if (write_locked_index(r->index, &lock, COMMIT_LOCK) < 0) {

sequencer.c

@@ -715,6 +715,8 @@ static int do_recursive_merge(struct repository *r,
 	o.show_rename_progress = 1;
 
 	head_tree = parse_tree_indirect(head);
+	if (!head_tree)
+		return error(_("unable to read tree %s"), oid_to_hex(head));
 	next_tree = next ? repo_get_commit_tree(r, next) : empty_tree(r);
 	base_tree = base ? repo_get_commit_tree(r, base) : empty_tree(r);
 
@@ -3887,6 +3889,8 @@ static int do_reset(struct repository *r,
 	}
 
 	tree = parse_tree_indirect(&oid);
+	if (!tree)
+		return error(_("unable to read tree %s"), oid_to_hex(&oid));
 	prime_cache_tree(r, r->index, tree);
 
 	if (write_locked_index(r->index, &lock, COMMIT_LOCK) < 0)