In the Linux kernel, the following vulnerability has been resolved:ext4: make sure the first directory block is not a holeThe syzbot constructs a directory that has no dirblock but is non-inline,i.e. the first directory block is a hole. And no errors are reported whencreating files in this directory in the following flow. ext4_mknod ... ext4_add_entry // Read block 0 ext4_read_dirblock(dir, block, DIRENT) bh = ext4_bread(NULL, inode, block, 0) if (!bh && (type == INDEX || type == DIRENT_HTREE)) // The first directory block is a hole // But type == DIRENT, so no error is reported.After that, we get a directory block without '.' and '..' but with a validdentry. This may cause some code that relies on dot or dotdot (such asmake_indexed_dir()) to crash.Therefore when ext4_read_dirblock() finds that the first directory blockis a hole report that the filesystem is corrupted and return an error toavoid loading corrupted data from disk causing something bad.
