CVE-2024-42304 Information

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.

Reference

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