ext4_utils: fix crash when filesystem size is too small

make_ext4fs crashes if size is less than block size or less than
header size (super block + descriptors + bitmaps). Check the size
and return errors.

Test: run make_ext4fs with small sizes
Bug: 36576677
Change-Id: I61d92e280cdf290054fadda5a045fc839c6fd8fe

2 files changed, 8 insertions, 5 deletions

diff --git a/ext4_utils/ext4_utils.c b/ext4_utils/ext4_utils.c
index 550181f3..07a92119 100644
--- a/ext4_utils/ext4_utils.c
+++ b/ext4_utils/ext4_utils.c
@@ -222,6 +222,9 @@ void ext4_create_fs_aux_info()
 	if (ext4_bg_has_super_block(aux_info.groups - 1))
 		last_header_size += 1 + aux_info.bg_desc_blocks +
 			info.bg_desc_reserve_blocks;
+	if (aux_info.groups <= 1 && last_group_size < last_header_size) {
+		critical_error("filesystem size too small");
+	}
 	if (last_group_size > 0 && last_group_size < last_header_size) {
 		aux_info.groups--;
 		aux_info.len_blocks -= last_group_size;
diff --git a/ext4_utils/make_ext4fs.c b/ext4_utils/make_ext4fs.c
index b84db9b3..58069f31 100644
--- a/ext4_utils/make_ext4fs.c
+++ b/ext4_utils/make_ext4fs.c
@@ -753,17 +753,17 @@ int make_ext4fs_internal(int fd, const char *_directory, const char *_target_out
 	if (info.len <= 0)
 		info.len = get_file_size(fd);
 
-	if (info.len <= 0) {
-		fprintf(stderr, "Need size of filesystem\n");
-		return EXIT_FAILURE;
-	}
-
 	if (info.block_size <= 0)
 		info.block_size = compute_block_size();
 
 	/* Round down the filesystem length to be a multiple of the block size */
 	info.len &= ~((u64)info.block_size - 1);
 
+	if (info.len <= 0) {
+		fprintf(stderr, "filesystem size too small\n");
+		return EXIT_FAILURE;
+	}
+
 	if (info.journal_blocks == 0)
 		info.journal_blocks = compute_journal_blocks();