CVE-2024-26982

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

Squashfs: check the inode number is not the invalid value of zero

Syskiller has produced an out of bounds access in fill_meta_index().

That out of bounds access is ultimately caused because the inode has an inode number with the invalid value of zero, which was not checked.

The reason this causes the out of bounds access is due to following sequence of events:

1. Fill_meta_index() is called to allocate (via empty_meta_index()) and fill a metadata index. It however suffers a data read error and aborts, invalidating the newly returned empty metadata index. It does this by setting the inode number of the index to zero, which means unused (zero is not a valid inode number).

2. When fill_meta_index() is subsequently called again on another read operation, locate_meta_index() returns the previous index because it matches the inode number of 0. Because this index has been returned it is expected to have been filled, and because it hasnt been, an out of bounds access is performed.

This patch adds a sanity check which checks that the inode number is not zero when the inode is created and returns -EINVAL if it is.

[phillip@squashfs.org.uk: whitespace fix]

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/32c114a58236fe67141634774559f21f1dc96fd7
• https://git.kernel.org/stable/c/4a1b6f89825e267e156ccaeba3d235edcac77f94
• https://git.kernel.org/stable/c/5b99dea79650b50909c50aba24fbae00f203f013
• https://git.kernel.org/stable/c/7def00ebc9f2d6a581ddf46ce4541f84a10680e5
• https://git.kernel.org/stable/c/9253c54e01b6505d348afbc02abaa4d9f8a01395
• https://git.kernel.org/stable/c/be383effaee3d89034f0828038f95065b518772e
• https://git.kernel.org/stable/c/cf46f88b92cfc0e32bd8a21ba1273cff13b8745f
• https://git.kernel.org/stable/c/7def00ebc9f2d6a581ddf46ce4541f84a10680e5
• https://git.kernel.org/stable/c/9253c54e01b6505d348afbc02abaa4d9f8a01395
• https://git.kernel.org/stable/c/be383effaee3d89034f0828038f95065b518772e
• https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
• https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/4EZ6PJW7VOZ224TD7N4JZNU6KV32ZJ53/
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/DAMSOZXJEPUOXW33WZYWCVAY7Z5S7OOY/
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GCBZZEC7L7KTWWAS2NLJK6SO3IZIL4WW/