linux-cve-announce - CVE-2024-42304: ext4: make sure the first directory block is not a hole

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Message-ID: <2024081749-CVE-2024-42304-d0e4@gregkh>
Date: Sat, 17 Aug 2024 11:10:09 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-42304: ext4: make sure the first directory block is not a hole

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.

The Linux kernel CVE team has assigned CVE-2024-42304 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.3 with commit 4e19d6b65fb4 and fixed in 6.1.103 with commit b609753cbbd3
	Issue introduced in 5.3 with commit 4e19d6b65fb4 and fixed in 6.6.44 with commit c3893d9de8ee
	Issue introduced in 5.3 with commit 4e19d6b65fb4 and fixed in 6.10.3 with commit 299bc6ffa57e
	Issue introduced in 5.3 with commit 4e19d6b65fb4 and fixed in 6.11-rc1 with commit f9ca51596bbf
	Issue introduced in 4.9.187 with commit 3f0307b0d2d8
	Issue introduced in 4.14.135 with commit 514631c2225c
	Issue introduced in 4.19.62 with commit 3a17ca864baf
	Issue introduced in 5.1.21 with commit 7f1f86276515
	Issue introduced in 5.2.4 with commit 5021b7a5bdd6

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-42304
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ext4/namei.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	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