[PATCH] lib/ext2fs: Validity checks for ext2fs_inode_scan_goto_blockgroup()

[Brian Norris <briannorris@chromium.org>]

We don't validate the 'group' argument, so it's easy to get underflows
or crashes here.

This resolves issues seen in ureadahead, when it uses an old packfile
(with mismatching group indices) with a new filesystem.

Signed-off-by: Brian Norris <briannorris@chromium.org>
---

 lib/ext2fs/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/ext2fs/inode.c b/lib/ext2fs/inode.c
index 957d5aa9f9d6..96d854b5fb69 100644
--- a/lib/ext2fs/inode.c
+++ b/lib/ext2fs/inode.c
@@ -313,6 +313,9 @@ static errcode_t get_next_blockgroup(ext2_inode_scan scan)
 errcode_t ext2fs_inode_scan_goto_blockgroup(ext2_inode_scan scan,
 					    int	group)
 {
+	if (group <= 0 || group >= scan->fs->group_desc_count)
+		return EXT2_ET_INVALID_ARGUMENT;
+
 	scan->current_group = group - 1;
 	scan->groups_left = scan->fs->group_desc_count - group;
 	scan->bad_block_ptr = 0;
-- 
2.43.0.rc2.451.g8631bc7472-goog