CVE-2024-42131

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

mm: avoid overflows in dirty throttling logic

The dirty throttling logic is interspersed with assumptions that dirty limits in PAGE_SIZE units fit into 32-bit (so that various multiplications fit into 64-bits). If limits end up being larger, we will hit overflows, possible divisions by 0 etc. Fix these problems by never allowing so large dirty limits as they have dubious practical value anyway. For dirty_bytes / dirty_background_bytes interfaces we can just refuse to set so large limits. For dirty_ratio / dirty_background_ratio it isnt so simple as the dirty limit is computed from the amount of available memory which can change due to memory hotplug etc. So when converting dirty limits from ratios to numbers of pages, we just dont allow the result to exceed UINT_MAX.

This is root-only triggerable problem which occurs when the operator sets dirty limits to >16 TB.

Weakness

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• If possible, choose a language or compiler that performs automatic bounds checking.
• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
• Use libraries or frameworks that make it easier to handle numbers without unexpected consequences.
• Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]
• Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
• Use unsigned integers where possible. This makes it easier to perform validation for integer overflows. When signed integers are required, ensure that the range check includes minimum values as well as maximum values.
• Understand the programming language’s underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, “not-a-number” calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-7]
• Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/92.html

References

• https://git.kernel.org/stable/c/2b2d2b8766db028bd827af34075f221ae9e9efff
• https://git.kernel.org/stable/c/385d838df280eba6c8680f9777bfa0d0bfe7e8b2
• https://git.kernel.org/stable/c/4d3817b64eda07491bdd86a234629fe0764fb42a
• https://git.kernel.org/stable/c/7a49389771ae7666f4dc3426e2a4594bf23ae290
• https://git.kernel.org/stable/c/8e0b5e7f2895eccef5c2a0018b589266f90c4805
• https://git.kernel.org/stable/c/a25e8536184516b55ef89ab91dd2eea429de28d2
• https://git.kernel.org/stable/c/bd16a7ee339aef3ee4c90cb23902afb6af379ea0
• https://git.kernel.org/stable/c/c83ed422c24f0d4b264f89291d4fabe285f80dbc
• https://git.kernel.org/stable/c/385d838df280eba6c8680f9777bfa0d0bfe7e8b2
• https://git.kernel.org/stable/c/7a49389771ae7666f4dc3426e2a4594bf23ae290
• https://git.kernel.org/stable/c/8e0b5e7f2895eccef5c2a0018b589266f90c4805
• https://git.kernel.org/stable/c/a25e8536184516b55ef89ab91dd2eea429de28d2
• https://git.kernel.org/stable/c/bd16a7ee339aef3ee4c90cb23902afb6af379ea0
• https://git.kernel.org/stable/c/c83ed422c24f0d4b264f89291d4fabe285f80dbc
• https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html