authfs/src/fsverity/verifier.rs - android_packages_modules_Virtualization - Gitiles

 /*
  * Copyright (C) 2020 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.
  */

 use libc::EIO;
 use std::io;

 use super::common::{build_fsverity_digest, merkle_tree_height, FsverityError, SHA256_HASH_SIZE};
 use crate::common::{divide_roundup, CHUNK_SIZE};
 use crate::file::{ChunkBuffer, ReadByChunk};
 use openssl::sha::{sha256, Sha256};

 const ZEROS: [u8; CHUNK_SIZE as usize] = [0u8; CHUNK_SIZE as usize];

 type HashBuffer = [u8; SHA256_HASH_SIZE];

 fn hash_with_padding(chunk: &[u8], pad_to: usize) -> HashBuffer {
     let padding_size = pad_to - chunk.len();
     let mut ctx = Sha256::new();
     ctx.update(chunk);
     ctx.update(&ZEROS[..padding_size]);
     ctx.finish()
 }

 fn verity_check<T: ReadByChunk>(
     chunk: &[u8],
     chunk_index: u64,
     file_size: u64,
     merkle_tree: &T,
 ) -> Result<HashBuffer, FsverityError> {
     // The caller should not be able to produce a chunk at the first place if `file_size` is 0. The
     // current implementation expects to crash when a `ReadByChunk` implementation reads
     // beyond the file size, including empty file.
     assert_ne!(file_size, 0);

     let chunk_hash = hash_with_padding(chunk, CHUNK_SIZE as usize);

     // When the file is smaller or equal to CHUNK_SIZE, the root of Merkle tree is defined as the
     // hash of the file content, plus padding.
     if file_size <= CHUNK_SIZE {
         return Ok(chunk_hash);
     }

     fsverity_walk(chunk_index, file_size, merkle_tree)?.try_fold(
         chunk_hash,
         |actual_hash, result| {
             let (merkle_chunk, hash_offset_in_chunk) = result?;
             let expected_hash =
                 &merkle_chunk[hash_offset_in_chunk..hash_offset_in_chunk + SHA256_HASH_SIZE];
             if actual_hash != expected_hash {
                 return Err(FsverityError::CannotVerify);
             }
             Ok(hash_with_padding(&merkle_chunk, CHUNK_SIZE as usize))
         },
     )
 }

 /// Given a chunk index and the size of the file, returns an iterator that walks the Merkle tree
 /// from the leaf to the root. The iterator carries the slice of the chunk/node as well as the
 /// offset of the child node's hash. It is up to the iterator user to use the node and hash,
 /// e.g. for the actual verification.
 #[allow(clippy::needless_collect)]
 fn fsverity_walk<T: ReadByChunk>(
     chunk_index: u64,
     file_size: u64,
     merkle_tree: &T,
 ) -> Result<impl Iterator<Item = Result<([u8; 4096], usize), FsverityError>> + '_, FsverityError> {
     let hashes_per_node = CHUNK_SIZE / SHA256_HASH_SIZE as u64;
     debug_assert_eq!(hashes_per_node, 128u64);
     let max_level = merkle_tree_height(file_size).expect("file should not be empty") as u32;
     let root_to_leaf_steps = (0..=max_level)
         .rev()
         .map(|x| {
             let leaves_per_hash = hashes_per_node.pow(x);
             let leaves_size_per_hash = CHUNK_SIZE * leaves_per_hash;
             let leaves_size_per_node = leaves_size_per_hash * hashes_per_node;
             let nodes_at_level = divide_roundup(file_size, leaves_size_per_node);
             let level_size = nodes_at_level * CHUNK_SIZE;
             let offset_in_level = (chunk_index / leaves_per_hash) * SHA256_HASH_SIZE as u64;
             (level_size, offset_in_level)
         })
         .scan(0, |level_offset, (level_size, offset_in_level)| {
             let this_level_offset = *level_offset;
             *level_offset += level_size;
             let global_hash_offset = this_level_offset + offset_in_level;
             Some(global_hash_offset)
         })
         .map(|global_hash_offset| {
             let chunk_index = global_hash_offset / CHUNK_SIZE;
             let hash_offset_in_chunk = (global_hash_offset % CHUNK_SIZE) as usize;
             (chunk_index, hash_offset_in_chunk)
         })
         .collect::<Vec<_>>(); // Needs to collect first to be able to reverse below.

     Ok(root_to_leaf_steps.into_iter().rev().map(move |(chunk_index, hash_offset_in_chunk)| {
         let mut merkle_chunk = [0u8; 4096];
         // read_chunk is supposed to return a full chunk, or an incomplete one at the end of the
         // file. In the incomplete case, the hash is calculated with 0-padding to the chunk size.
         // Therefore, we don't need to check the returned size here.
         let _ = merkle_tree.read_chunk(chunk_index, &mut merkle_chunk)?;
         Ok((merkle_chunk, hash_offset_in_chunk))
     }))
 }

 pub struct VerifiedFileReader<F: ReadByChunk, M: ReadByChunk> {
     pub file_size: u64,
     chunked_file: F,
     merkle_tree: M,
     root_hash: HashBuffer,
 }

 impl<F: ReadByChunk, M: ReadByChunk> VerifiedFileReader<F, M> {
     pub fn new(
         chunked_file: F,
         file_size: u64,
         expected_digest: &[u8],
         merkle_tree: M,
     ) -> Result<VerifiedFileReader<F, M>, FsverityError> {
         let mut buf = [0u8; CHUNK_SIZE as usize];
         if file_size <= CHUNK_SIZE {
             let _size = chunked_file.read_chunk(0, &mut buf)?;
             // The rest of buffer is 0-padded.
         } else {
             let size = merkle_tree.read_chunk(0, &mut buf)?;
             if buf.len() != size {
                 return Err(FsverityError::InsufficientData(size));
             }
         }
         let root_hash = sha256(&buf[..]);
         if expected_digest == build_fsverity_digest(&root_hash, file_size) {
             // Once verified, use the root_hash for verification going forward.
             Ok(VerifiedFileReader { chunked_file, file_size, merkle_tree, root_hash })
         } else {
             Err(FsverityError::InvalidDigest)
         }
     }
 }

 impl<F: ReadByChunk, M: ReadByChunk> ReadByChunk for VerifiedFileReader<F, M> {
     fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
         let size = self.chunked_file.read_chunk(chunk_index, buf)?;
         let root_hash = verity_check(&buf[..size], chunk_index, self.file_size, &self.merkle_tree)
             .map_err(|_| io::Error::from_raw_os_error(EIO))?;
         if root_hash != self.root_hash {
             Err(io::Error::from_raw_os_error(EIO))
         } else {
             Ok(size)
         }
     }
 }

 #[cfg(test)]
 mod tests {
     use super::*;
     use crate::file::ReadByChunk;
     use anyhow::Result;
     use authfs_fsverity_metadata::{parse_fsverity_metadata, FSVerityMetadata};
     use std::cmp::min;
     use std::fs::File;
     use std::os::unix::fs::FileExt;

     struct LocalFileReader {
         file: File,
         size: u64,
     }

     impl LocalFileReader {
         fn new(file: File) -> io::Result<LocalFileReader> {
             let size = file.metadata()?.len();
             Ok(LocalFileReader { file, size })
         }

         fn len(&self) -> u64 {
             self.size
         }
     }

     impl ReadByChunk for LocalFileReader {
         fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
             let start = chunk_index * CHUNK_SIZE;
             if start >= self.size {
                 return Ok(0);
             }
             let end = min(self.size, start + CHUNK_SIZE);
             let read_size = (end - start) as usize;
             debug_assert!(read_size <= buf.len());
             self.file.read_exact_at(&mut buf[..read_size], start)?;
             Ok(read_size)
         }
     }

     type LocalVerifiedFileReader = VerifiedFileReader<LocalFileReader, MerkleTreeReader>;

     pub struct MerkleTreeReader {
         metadata: Box<FSVerityMetadata>,
     }

     impl ReadByChunk for MerkleTreeReader {
         fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
             self.metadata.read_merkle_tree(chunk_index * CHUNK_SIZE, buf)
         }
     }

     fn total_chunk_number(file_size: u64) -> u64 {
         (file_size + 4095) / 4096
     }

     // Returns a reader with fs-verity verification and the file size.
     fn new_reader_with_fsverity(
         content_path: &str,
         metadata_path: &str,
     ) -> Result<(LocalVerifiedFileReader, u64)> {
         let file_reader = LocalFileReader::new(File::open(content_path)?)?;
         let file_size = file_reader.len();
         let metadata = parse_fsverity_metadata(File::open(metadata_path)?)?;
         Ok((
             VerifiedFileReader::new(
                 file_reader,
                 file_size,
                 &metadata.digest.clone(),
                 MerkleTreeReader { metadata },
             )?,
             file_size,
         ))
     }

     #[test]
     fn fsverity_verify_full_read_4k() -> Result<()> {
         let (file_reader, file_size) =
             new_reader_with_fsverity("testdata/input.4k", "testdata/input.4k.fsv_meta")?;

         for i in 0..total_chunk_number(file_size) {
             let mut buf = [0u8; 4096];
             assert!(file_reader.read_chunk(i, &mut buf).is_ok());
         }
         Ok(())
     }

     #[test]
     fn fsverity_verify_full_read_4k1() -> Result<()> {
         let (file_reader, file_size) =
             new_reader_with_fsverity("testdata/input.4k1", "testdata/input.4k1.fsv_meta")?;

         for i in 0..total_chunk_number(file_size) {
             let mut buf = [0u8; 4096];
             assert!(file_reader.read_chunk(i, &mut buf).is_ok());
         }
         Ok(())
     }

     #[test]
     fn fsverity_verify_full_read_4m() -> Result<()> {
         let (file_reader, file_size) =
             new_reader_with_fsverity("testdata/input.4m", "testdata/input.4m.fsv_meta")?;

         for i in 0..total_chunk_number(file_size) {
             let mut buf = [0u8; 4096];
             assert!(file_reader.read_chunk(i, &mut buf).is_ok());
         }
         Ok(())
     }

     #[test]
     fn fsverity_verify_bad_merkle_tree() -> Result<()> {
         let (file_reader, _) = new_reader_with_fsverity(
             "testdata/input.4m",
             "testdata/input.4m.fsv_meta.bad_merkle", // First leaf node is corrupted.
         )?;

         // A lowest broken node (a 4K chunk that contains 128 sha256 hashes) will fail the read
         // failure of the underlying chunks, but not before or after.
         let mut buf = [0u8; 4096];
         let num_hashes = 4096 / 32;
         let last_index = num_hashes;
         for i in 0..last_index {
             assert!(file_reader.read_chunk(i, &mut buf).is_err());
         }
         assert!(file_reader.read_chunk(last_index, &mut buf).is_ok());
         Ok(())
     }
 }
	/*
	* Copyright (C) 2020 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.
	*/

	use libc::EIO;
	use std::io;

	use super::common::{build_fsverity_digest, merkle_tree_height, FsverityError, SHA256_HASH_SIZE};
	use crate::common::{divide_roundup, CHUNK_SIZE};
	use crate::file::{ChunkBuffer, ReadByChunk};
	use openssl::sha::{sha256, Sha256};

	const ZEROS: [u8; CHUNK_SIZE as usize] = [0u8; CHUNK_SIZE as usize];

	type HashBuffer = [u8; SHA256_HASH_SIZE];

	fn hash_with_padding(chunk: &[u8], pad_to: usize) -> HashBuffer {
	let padding_size = pad_to - chunk.len();
	let mut ctx = Sha256::new();
	ctx.update(chunk);
	ctx.update(&ZEROS[..padding_size]);
	ctx.finish()
	}

	fn verity_check<T: ReadByChunk>(
	chunk: &[u8],
	chunk_index: u64,
	file_size: u64,
	merkle_tree: &T,
	) -> Result<HashBuffer, FsverityError> {
	// The caller should not be able to produce a chunk at the first place if `file_size` is 0. The
	// current implementation expects to crash when a `ReadByChunk` implementation reads
	// beyond the file size, including empty file.
	assert_ne!(file_size, 0);

	let chunk_hash = hash_with_padding(chunk, CHUNK_SIZE as usize);

	// When the file is smaller or equal to CHUNK_SIZE, the root of Merkle tree is defined as the
	// hash of the file content, plus padding.
	if file_size <= CHUNK_SIZE {
	return Ok(chunk_hash);
	}

	fsverity_walk(chunk_index, file_size, merkle_tree)?.try_fold(
	chunk_hash,
	\|actual_hash, result\| {
	let (merkle_chunk, hash_offset_in_chunk) = result?;
	let expected_hash =
	&merkle_chunk[hash_offset_in_chunk..hash_offset_in_chunk + SHA256_HASH_SIZE];
	if actual_hash != expected_hash {
	return Err(FsverityError::CannotVerify);
	}
	Ok(hash_with_padding(&merkle_chunk, CHUNK_SIZE as usize))
	},
	)
	}

	/// Given a chunk index and the size of the file, returns an iterator that walks the Merkle tree
	/// from the leaf to the root. The iterator carries the slice of the chunk/node as well as the
	/// offset of the child node's hash. It is up to the iterator user to use the node and hash,
	/// e.g. for the actual verification.
	#[allow(clippy::needless_collect)]
	fn fsverity_walk<T: ReadByChunk>(
	chunk_index: u64,
	file_size: u64,
	merkle_tree: &T,
	) -> Result<impl Iterator<Item = Result<([u8; 4096], usize), FsverityError>> + '_, FsverityError> {
	let hashes_per_node = CHUNK_SIZE / SHA256_HASH_SIZE as u64;
	debug_assert_eq!(hashes_per_node, 128u64);
	let max_level = merkle_tree_height(file_size).expect("file should not be empty") as u32;
	let root_to_leaf_steps = (0..=max_level)
	.rev()
	.map(\|x\| {
	let leaves_per_hash = hashes_per_node.pow(x);
	let leaves_size_per_hash = CHUNK_SIZE * leaves_per_hash;
	let leaves_size_per_node = leaves_size_per_hash * hashes_per_node;
	let nodes_at_level = divide_roundup(file_size, leaves_size_per_node);
	let level_size = nodes_at_level * CHUNK_SIZE;
	let offset_in_level = (chunk_index / leaves_per_hash) * SHA256_HASH_SIZE as u64;
	(level_size, offset_in_level)
	})
	.scan(0, \|level_offset, (level_size, offset_in_level)\| {
	let this_level_offset = *level_offset;
	*level_offset += level_size;
	let global_hash_offset = this_level_offset + offset_in_level;
	Some(global_hash_offset)
	})
	.map(\|global_hash_offset\| {
	let chunk_index = global_hash_offset / CHUNK_SIZE;
	let hash_offset_in_chunk = (global_hash_offset % CHUNK_SIZE) as usize;
	(chunk_index, hash_offset_in_chunk)
	})
	.collect::<Vec<_>>(); // Needs to collect first to be able to reverse below.

	Ok(root_to_leaf_steps.into_iter().rev().map(move \|(chunk_index, hash_offset_in_chunk)\| {
	let mut merkle_chunk = [0u8; 4096];
	// read_chunk is supposed to return a full chunk, or an incomplete one at the end of the
	// file. In the incomplete case, the hash is calculated with 0-padding to the chunk size.
	// Therefore, we don't need to check the returned size here.
	let _ = merkle_tree.read_chunk(chunk_index, &mut merkle_chunk)?;
	Ok((merkle_chunk, hash_offset_in_chunk))
	}))
	}

	pub struct VerifiedFileReader<F: ReadByChunk, M: ReadByChunk> {
	pub file_size: u64,
	chunked_file: F,
	merkle_tree: M,
	root_hash: HashBuffer,
	}

	impl<F: ReadByChunk, M: ReadByChunk> VerifiedFileReader<F, M> {
	pub fn new(
	chunked_file: F,
	file_size: u64,
	expected_digest: &[u8],
	merkle_tree: M,
	) -> Result<VerifiedFileReader<F, M>, FsverityError> {
	let mut buf = [0u8; CHUNK_SIZE as usize];
	if file_size <= CHUNK_SIZE {
	let _size = chunked_file.read_chunk(0, &mut buf)?;
	// The rest of buffer is 0-padded.
	} else {
	let size = merkle_tree.read_chunk(0, &mut buf)?;
	if buf.len() != size {
	return Err(FsverityError::InsufficientData(size));
	}
	}
	let root_hash = sha256(&buf[..]);
	if expected_digest == build_fsverity_digest(&root_hash, file_size) {
	// Once verified, use the root_hash for verification going forward.
	Ok(VerifiedFileReader { chunked_file, file_size, merkle_tree, root_hash })
	} else {
	Err(FsverityError::InvalidDigest)
	}
	}
	}

	impl<F: ReadByChunk, M: ReadByChunk> ReadByChunk for VerifiedFileReader<F, M> {
	fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
	let size = self.chunked_file.read_chunk(chunk_index, buf)?;
	let root_hash = verity_check(&buf[..size], chunk_index, self.file_size, &self.merkle_tree)
	.map_err(\|_\| io::Error::from_raw_os_error(EIO))?;
	if root_hash != self.root_hash {
	Err(io::Error::from_raw_os_error(EIO))
	} else {
	Ok(size)
	}
	}
	}

	#[cfg(test)]
	mod tests {
	use super::*;
	use crate::file::ReadByChunk;
	use anyhow::Result;
	use authfs_fsverity_metadata::{parse_fsverity_metadata, FSVerityMetadata};
	use std::cmp::min;
	use std::fs::File;
	use std::os::unix::fs::FileExt;

	struct LocalFileReader {
	file: File,
	size: u64,
	}

	impl LocalFileReader {
	fn new(file: File) -> io::Result<LocalFileReader> {
	let size = file.metadata()?.len();
	Ok(LocalFileReader { file, size })
	}

	fn len(&self) -> u64 {
	self.size
	}
	}

	impl ReadByChunk for LocalFileReader {
	fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
	let start = chunk_index * CHUNK_SIZE;
	if start >= self.size {
	return Ok(0);
	}
	let end = min(self.size, start + CHUNK_SIZE);
	let read_size = (end - start) as usize;
	debug_assert!(read_size <= buf.len());
	self.file.read_exact_at(&mut buf[..read_size], start)?;
	Ok(read_size)
	}
	}

	type LocalVerifiedFileReader = VerifiedFileReader<LocalFileReader, MerkleTreeReader>;

	pub struct MerkleTreeReader {
	metadata: Box<FSVerityMetadata>,
	}

	impl ReadByChunk for MerkleTreeReader {
	fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
	self.metadata.read_merkle_tree(chunk_index * CHUNK_SIZE, buf)
	}
	}

	fn total_chunk_number(file_size: u64) -> u64 {
	(file_size + 4095) / 4096
	}

	// Returns a reader with fs-verity verification and the file size.
	fn new_reader_with_fsverity(
	content_path: &str,
	metadata_path: &str,
	) -> Result<(LocalVerifiedFileReader, u64)> {
	let file_reader = LocalFileReader::new(File::open(content_path)?)?;
	let file_size = file_reader.len();
	let metadata = parse_fsverity_metadata(File::open(metadata_path)?)?;
	Ok((
	VerifiedFileReader::new(
	file_reader,
	file_size,
	&metadata.digest.clone(),
	MerkleTreeReader { metadata },
	)?,
	file_size,
	))
	}

	#[test]
	fn fsverity_verify_full_read_4k() -> Result<()> {
	let (file_reader, file_size) =
	new_reader_with_fsverity("testdata/input.4k", "testdata/input.4k.fsv_meta")?;

	for i in 0..total_chunk_number(file_size) {
	let mut buf = [0u8; 4096];
	assert!(file_reader.read_chunk(i, &mut buf).is_ok());
	}
	Ok(())
	}

	#[test]
	fn fsverity_verify_full_read_4k1() -> Result<()> {
	let (file_reader, file_size) =
	new_reader_with_fsverity("testdata/input.4k1", "testdata/input.4k1.fsv_meta")?;

	for i in 0..total_chunk_number(file_size) {
	let mut buf = [0u8; 4096];
	assert!(file_reader.read_chunk(i, &mut buf).is_ok());
	}
	Ok(())
	}

	#[test]
	fn fsverity_verify_full_read_4m() -> Result<()> {
	let (file_reader, file_size) =
	new_reader_with_fsverity("testdata/input.4m", "testdata/input.4m.fsv_meta")?;

	for i in 0..total_chunk_number(file_size) {
	let mut buf = [0u8; 4096];
	assert!(file_reader.read_chunk(i, &mut buf).is_ok());
	}
	Ok(())
	}

	#[test]
	fn fsverity_verify_bad_merkle_tree() -> Result<()> {
	let (file_reader, _) = new_reader_with_fsverity(
	"testdata/input.4m",
	"testdata/input.4m.fsv_meta.bad_merkle", // First leaf node is corrupted.
	)?;

	// A lowest broken node (a 4K chunk that contains 128 sha256 hashes) will fail the read
	// failure of the underlying chunks, but not before or after.
	let mut buf = [0u8; 4096];
	let num_hashes = 4096 / 32;
	let last_index = num_hashes;
	for i in 0..last_index {
	assert!(file_reader.read_chunk(i, &mut buf).is_err());
	}
	assert!(file_reader.read_chunk(last_index, &mut buf).is_ok());
	Ok(())
	}
	}