libs/bssl/src/digest.rs

// Copyright 2023, The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Wrappers of the digest functions in BoringSSL digest.h.

use crate::util::{check_int_result, to_call_failed_error};
use alloc::vec;
use alloc::vec::Vec;
use bssl_avf_error::{ApiName, Error, Result};
use bssl_ffi::{
    EVP_Digest, EVP_MD_CTX_free, EVP_MD_CTX_new, EVP_MD_size, EVP_sha256, EVP_sha384, EVP_sha512,
    EVP_MAX_MD_SIZE, EVP_MD, EVP_MD_CTX,
};
use core::ptr::{self, NonNull};
use log::error;

const MAX_DIGEST_SIZE: usize = EVP_MAX_MD_SIZE as usize;

/// Message digester wrapping `EVP_MD`.
#[derive(Clone, Debug)]
pub struct Digester(pub(crate) &'static EVP_MD);

impl Digester {
    /// Returns a `Digester` implementing `SHA-256` algorithm.
    pub fn sha256() -> Self {
        // SAFETY: This function does not access any Rust variables and simply returns
        // a pointer to the static variable in BoringSSL.
        let p = unsafe { EVP_sha256() };
        // SAFETY: The returned pointer should always be valid and points to a static
        // `EVP_MD`.
        Self(unsafe { p.as_ref().unwrap() })
    }

    /// Returns a `Digester` implementing `SHA-384` algorithm.
    pub fn sha384() -> Self {
        // SAFETY: This function does not access any Rust variables and simply returns
        // a pointer to the static variable in BoringSSL.
        let p = unsafe { EVP_sha384() };
        // SAFETY: The returned pointer should always be valid and points to a static
        // `EVP_MD`.
        Self(unsafe { p.as_ref().unwrap() })
    }

    /// Returns a `Digester` implementing `SHA-512` algorithm.
    pub fn sha512() -> Self {
        // SAFETY: This function does not access any Rust variables and simply returns
        // a pointer to the static variable in BoringSSL.
        let p = unsafe { EVP_sha512() };
        // SAFETY: The returned pointer should always be valid and points to a static
        // `EVP_MD`.
        Self(unsafe { p.as_ref().unwrap() })
    }

    /// Returns the digest size in bytes.
    pub fn size(&self) -> usize {
        // SAFETY: The inner pointer is fetched from EVP_* hash functions in BoringSSL digest.h
        unsafe { EVP_MD_size(self.0) }
    }

    /// Computes the digest of the provided `data`.
    pub fn digest(&self, data: &[u8]) -> Result<Vec<u8>> {
        let mut out = vec![0u8; MAX_DIGEST_SIZE];
        let mut out_size = 0;
        let engine = ptr::null_mut(); // Use the default engine.
        let ret =
            // SAFETY: This function reads `data` and writes to `out` within its bounds.
            // `out` has `MAX_DIGEST_SIZE` bytes of space for write as required in the
            // BoringSSL spec.
            // The digester is a valid pointer to a static `EVP_MD` as it is returned by
            // BoringSSL API during the construction of this struct.
            unsafe {
                EVP_Digest(
                    data.as_ptr() as *const _,
                    data.len(),
                    out.as_mut_ptr(),
                    &mut out_size,
                    self.0,
                    engine,
                )
            };
        check_int_result(ret, ApiName::EVP_Digest)?;
        let out_size = usize::try_from(out_size).map_err(|e| {
            error!("Failed to convert digest size to usize: {:?}", e);
            Error::InternalError
        })?;
        if self.size() != out_size {
            return Err(to_call_failed_error(ApiName::EVP_Digest));
        }
        out.truncate(out_size);
        Ok(out)
    }
}

/// Message digester context wrapping `EVP_MD_CTX`.
#[derive(Clone, Debug)]
pub struct DigesterContext(NonNull<EVP_MD_CTX>);

impl Drop for DigesterContext {
    fn drop(&mut self) {
        // SAFETY: This function frees any resources owned by `EVP_MD_CTX` and resets it to a
        // freshly initialised state and then frees the context.
        // It is safe because `EVP_MD_CTX` has been allocated by BoringSSL and isn't used after
        // this.
        unsafe { EVP_MD_CTX_free(self.0.as_ptr()) }
    }
}

impl DigesterContext {
    /// Creates a new `DigesterContext` wrapping a freshly allocated and initialised `EVP_MD_CTX`.
    pub fn new() -> Result<Self> {
        // SAFETY: The returned pointer is checked below.
        let ctx = unsafe { EVP_MD_CTX_new() };
        NonNull::new(ctx).map(Self).ok_or(to_call_failed_error(ApiName::EVP_MD_CTX_new))
    }

    pub(crate) fn as_mut_ptr(&mut self) -> *mut EVP_MD_CTX {
        self.0.as_ptr()
    }
}