ext4: make sure the first directory block is not a hole

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: ext4: make sure the first directory block is not a hole The 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 when creating 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 valid dentry. This may cause some code that relies on dot or dotdot (such as make_indexed_dir()) to crash. Therefore when ext4_read_dirblock() finds that the first directory block is a hole report that the filesystem is corrupted and return an error to avoid loading corrupted data from disk causing something bad.

References

• https://git.kernel.org/stable/c/d81d7e347d1f1f48a5634607d39eb90c161c8afe
• https://git.kernel.org/stable/c/e02f9941e8c011aa3eafa799def6a134ce06bcfa
• https://git.kernel.org/stable/c/de2a011a13a46468a6e8259db58b1b62071fe136
• https://git.kernel.org/stable/c/9771e3d8365ae1dd5e8846a204cb9af14e3e656a
• https://git.kernel.org/stable/c/b609753cbbd38f8c0affd4956c0af178348523ac
• https://git.kernel.org/stable/c/c3893d9de8ee153baac56d127d844103488133b5
• https://git.kernel.org/stable/c/299bc6ffa57e04e74c6cce866d6c0741fb4897a1
• https://git.kernel.org/stable/c/f9ca51596bbfd0f9c386dd1c613c394c78d9e5e6