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

Vulnerability Description

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 implementation's ->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().

References

• https://git.kernel.org/stable/c/f02f0218be412cff1c844addf58e002071be298b
• https://git.kernel.org/stable/c/f2133b849ff273abddb6da622daddd8f6f6fa448
• https://git.kernel.org/stable/c/921b8167f10708e38080f84e195cdc68a7a561f1
• https://git.kernel.org/stable/c/b16510a530d1e6ab9683f04f8fb34f2e0f538275