CVE-2024-46744

In the Linux kernel, the following vulnerability has been resolved:

Squashfs: sanity check symbolic link size

Syzkiller reports a KMSAN: uninit-value in pick_link bug.

This is caused by an uninitialised page, which is ultimately caused by a corrupted symbolic link size read from disk.

The reason why the corrupted symlink size causes an uninitialised page is due to the following sequence of events:

1. squashfs_read_inode() is called to read the symbolic link from disk. This assigns the corrupted value 3875536935 to inode->i_size.

2. Later squashfs_symlink_read_folio() is called, which assigns this corrupted value to the length variable, which being a signed int, overflows producing a negative number.

3. The following loop that fills in the page contents checks that the copied bytes is less than length, which being negative means the loop is skipped, producing an uninitialised page.

This patch adds a sanity check which checks that the symbolic link size is not larger than expected.

–

V2: fix spelling mistake.

Weakness

The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

Affected Software

Potential Mitigations

• Follow the principle of least privilege when assigning access rights to entities in a software system.
• Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/132.html
• https://cwe.mitre.org/data/definitions/17.html
• https://cwe.mitre.org/data/definitions/35.html
• https://cwe.mitre.org/data/definitions/76.html

References

• https://git.kernel.org/stable/c/087f25b2d36adae19951114ffcbb7106ed405ebb
• https://git.kernel.org/stable/c/1b9451ba6f21478a75288ea3e3fca4be35e2a438
• https://git.kernel.org/stable/c/5c8906de98d0d7ad42ff3edf2cb6cd7e0ea658c4
• https://git.kernel.org/stable/c/810ee43d9cd245d138a2733d87a24858a23f577d
• https://git.kernel.org/stable/c/c3af7e460a526007e4bed1ce3623274a1a6afe5e
• https://git.kernel.org/stable/c/ef4e249971eb77ec33d74c5c3de1e2576faf6c90
• https://git.kernel.org/stable/c/f82cb7f24032ed023fc67d26ea9bf322d8431a90
• https://git.kernel.org/stable/c/fac5e82ab1334fc8ed6ff7183702df634bd1d93d