CVE-2025-37984

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

crypto: ecdsa - Harden against integer overflows in DIV_ROUND_UP()

Herbert notes that DIV_ROUND_UP() may overflow unnecessarily if an ecdsa implementations ->key_size() callback returns an unusually large value. Herbert instead suggests (for a division by 8):

X / 8 + !!(X & 7)

Based on this formula, introduce a generic DIV_ROUND_UP_POW2() macro and use it in lieu of DIV_ROUND_UP() for ->key_size() return values.

Additionally, use the macro in ecc_digits_from_bytes(), whose nbytes parameter is a ->key_size() return value in some instances, or a user-specified ASN.1 length in the case of ecdsa_get_signature_rs().

Affected Software

References

• https://git.kernel.org/stable/c/921b8167f10708e38080f84e195cdc68a7a561f1
• https://git.kernel.org/stable/c/b16510a530d1e6ab9683f04f8fb34f2e0f538275