authfs/fd_server/src/aidl.rs - android_packages_modules_Virtualization - Gitiles

 /*
  * Copyright (C) 2021 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 anyhow::Result;
 use log::error;
 use nix::{
     errno::Errno, fcntl::openat, fcntl::OFlag, sys::stat::fchmod, sys::stat::mkdirat,
     sys::stat::mode_t, sys::stat::Mode, sys::statvfs::statvfs, sys::statvfs::Statvfs,
     unistd::unlinkat, unistd::UnlinkatFlags,
 };
 use std::cmp::min;
 use std::collections::{btree_map, BTreeMap};
 use std::convert::TryInto;
 use std::fs::File;
 use std::io;
 use std::os::unix::fs::FileExt;
 use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, OwnedFd};
 use std::path::{Component, Path, PathBuf, MAIN_SEPARATOR};
 use std::sync::{Arc, RwLock};

 use authfs_aidl_interface::aidl::com::android::virt::fs::IVirtFdService::{
     BnVirtFdService, FsStat::FsStat, IVirtFdService, MAX_REQUESTING_DATA,
 };
 use authfs_fsverity_metadata::{
     get_fsverity_metadata_path, parse_fsverity_metadata, FSVerityMetadata,
 };
 use binder::{
     BinderFeatures, ExceptionCode, Interface, Result as BinderResult, Status, StatusCode, Strong,
 };

 /// Bitflags of forbidden file mode, e.g. setuid, setgid and sticky bit.
 const FORBIDDEN_MODES: Mode = Mode::from_bits_truncate(!0o777);

 /// Configuration of a file descriptor to be served/exposed/shared.
 pub enum FdConfig {
     /// A read-only file to serve by this server. The file is supposed to be verifiable with the
     /// associated fs-verity metadata.
     Readonly {
         /// The file to read from. fs-verity metadata can be retrieved from this file's FD.
         file: File,

         // Alternative metadata storing merkle tree and signature.
         alt_metadata: Option<Box<FSVerityMetadata>>,
     },

     /// A readable/writable file to serve by this server. This backing file should just be a
     /// regular file and does not have any specific property.
     ReadWrite(File),

     /// A read-only directory to serve by this server.
     InputDir(OwnedFd),

     /// A writable directory to serve by this server.
     OutputDir(OwnedFd),
 }

 pub struct FdService {
     /// A pool of opened files and directories, which can be looked up by the FD number.
     fd_pool: Arc<RwLock<BTreeMap<i32, FdConfig>>>,
 }

 impl FdService {
     pub fn new_binder(fd_pool: BTreeMap<i32, FdConfig>) -> Strong<dyn IVirtFdService> {
         BnVirtFdService::new_binder(
             FdService { fd_pool: Arc::new(RwLock::new(fd_pool)) },
             BinderFeatures::default(),
         )
     }

     /// Handles the requesting file `id` with `handle_fn` if it is in the FD pool. This function
     /// returns whatever `handle_fn` returns.
     fn handle_fd<F, R>(&self, id: i32, handle_fn: F) -> BinderResult<R>
     where
         F: FnOnce(&FdConfig) -> BinderResult<R>,
     {
         let fd_pool = self.fd_pool.read().unwrap();
         let fd_config = fd_pool.get(&id).ok_or_else(|| new_errno_error(Errno::EBADF))?;
         handle_fn(fd_config)
     }

     /// Inserts a new FD and corresponding `FdConfig` created by `create_fn` to the FD pool, then
     /// returns the new FD number.
     fn insert_new_fd<F>(&self, fd: i32, create_fn: F) -> BinderResult<i32>
     where
         F: FnOnce(&mut FdConfig) -> BinderResult<(i32, FdConfig)>,
     {
         let mut fd_pool = self.fd_pool.write().unwrap();
         let fd_config = fd_pool.get_mut(&fd).ok_or_else(|| new_errno_error(Errno::EBADF))?;
         let (new_fd, new_fd_config) = create_fn(fd_config)?;
         if let btree_map::Entry::Vacant(entry) = fd_pool.entry(new_fd) {
             entry.insert(new_fd_config);
             Ok(new_fd)
         } else {
             Err(Status::new_exception_str(
                 ExceptionCode::ILLEGAL_STATE,
                 Some(format!(
                     "The newly created FD {} is already in the pool unexpectedly",
                     new_fd
                 )),
             ))
         }
     }
 }

 impl Interface for FdService {}

 impl IVirtFdService for FdService {
     fn readFile(&self, id: i32, offset: i64, size: i32) -> BinderResult<Vec<u8>> {
         let size: usize = validate_and_cast_size(size)?;
         let offset: u64 = validate_and_cast_offset(offset)?;

         self.handle_fd(id, |config| match config {
             FdConfig::Readonly { file, .. } | FdConfig::ReadWrite(file) => {
                 read_into_buf(file, size, offset).map_err(|e| {
                     error!("readFile: read error: {}", e);
                     new_errno_error(Errno::EIO)
                 })
             }
             FdConfig::InputDir(_) | FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
         })
     }

     fn readFsverityMerkleTree(&self, id: i32, offset: i64, size: i32) -> BinderResult<Vec<u8>> {
         let size: usize = validate_and_cast_size(size)?;
         let offset: u64 = validate_and_cast_offset(offset)?;

         self.handle_fd(id, |config| match config {
             FdConfig::Readonly { file, alt_metadata, .. } => {
                 let mut buf = vec![0; size];

                 let s = if let Some(metadata) = &alt_metadata {
                     metadata.read_merkle_tree(offset, &mut buf).map_err(|e| {
                         error!("readFsverityMerkleTree: read error: {}", e);
                         new_errno_error(Errno::EIO)
                     })?
                 } else {
                     fsverity::read_merkle_tree(file.as_raw_fd(), offset, &mut buf).map_err(|e| {
                         error!("readFsverityMerkleTree: failed to retrieve merkle tree: {}", e);
                         new_errno_error(Errno::EIO)
                     })?
                 };
                 debug_assert!(s <= buf.len(), "Shouldn't return more bytes than asked");
                 buf.truncate(s);
                 Ok(buf)
             }
             FdConfig::ReadWrite(_file) => {
                 // For a writable file, Merkle tree is not expected to be served since Auth FS
                 // doesn't trust it anyway. Auth FS may keep the Merkle tree privately for its own
                 // use.
                 Err(new_errno_error(Errno::ENOSYS))
             }
             FdConfig::InputDir(_) | FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
         })
     }

     fn readFsveritySignature(&self, id: i32) -> BinderResult<Vec<u8>> {
         self.handle_fd(id, |config| match config {
             FdConfig::Readonly { file, alt_metadata, .. } => {
                 if let Some(metadata) = &alt_metadata {
                     if let Some(signature) = &metadata.signature {
                         Ok(signature.clone())
                     } else {
                         Err(Status::new_service_specific_error_str(
                             -1,
                             Some("metadata doesn't contain a signature"),
                         ))
                     }
                 } else {
                     let mut buf = vec![0; MAX_REQUESTING_DATA as usize];
                     let s = fsverity::read_signature(file.as_raw_fd(), &mut buf).map_err(|e| {
                         error!("readFsverityMerkleTree: failed to retrieve merkle tree: {}", e);
                         new_errno_error(Errno::EIO)
                     })?;
                     debug_assert!(s <= buf.len(), "Shouldn't return more bytes than asked");
                     buf.truncate(s);
                     Ok(buf)
                 }
             }
             FdConfig::ReadWrite(_file) => {
                 // There is no signature for a writable file.
                 Err(new_errno_error(Errno::ENOSYS))
             }
             FdConfig::InputDir(_) | FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
         })
     }

     fn writeFile(&self, id: i32, buf: &[u8], offset: i64) -> BinderResult<i32> {
         self.handle_fd(id, |config| match config {
             FdConfig::Readonly { .. } => Err(StatusCode::INVALID_OPERATION.into()),
             FdConfig::ReadWrite(file) => {
                 let offset: u64 = offset.try_into().map_err(|_| new_errno_error(Errno::EINVAL))?;
                 // Check buffer size just to make `as i32` safe below.
                 if buf.len() > i32::MAX as usize {
                     return Err(new_errno_error(Errno::EOVERFLOW));
                 }
                 Ok(file.write_at(buf, offset).map_err(|e| {
                     error!("writeFile: write error: {}", e);
                     new_errno_error(Errno::EIO)
                 })? as i32)
             }
             FdConfig::InputDir(_) | FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
         })
     }

     fn resize(&self, id: i32, size: i64) -> BinderResult<()> {
         self.handle_fd(id, |config| match config {
             FdConfig::Readonly { .. } => Err(StatusCode::INVALID_OPERATION.into()),
             FdConfig::ReadWrite(file) => {
                 if size < 0 {
                     return Err(new_errno_error(Errno::EINVAL));
                 }
                 file.set_len(size as u64).map_err(|e| {
                     error!("resize: set_len error: {}", e);
                     new_errno_error(Errno::EIO)
                 })
             }
             FdConfig::InputDir(_) | FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
         })
     }

     fn getFileSize(&self, id: i32) -> BinderResult<i64> {
         self.handle_fd(id, |config| match config {
             FdConfig::Readonly { file, .. } => {
                 let size = file
                     .metadata()
                     .map_err(|e| {
                         error!("getFileSize error: {}", e);
                         new_errno_error(Errno::EIO)
                     })?
                     .len();
                 Ok(size.try_into().map_err(|e| {
                     error!("getFileSize: File too large: {}", e);
                     new_errno_error(Errno::EFBIG)
                 })?)
             }
             FdConfig::ReadWrite(_file) => {
                 // Content and metadata of a writable file needs to be tracked by authfs, since
                 // fd_server isn't considered trusted. So there is no point to support getFileSize
                 // for a writable file.
                 Err(new_errno_error(Errno::ENOSYS))
             }
             FdConfig::InputDir(_) | FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
         })
     }

     fn openFileInDirectory(&self, dir_fd: i32, file_path: &str) -> BinderResult<i32> {
         let path_buf = PathBuf::from(file_path);
         // Checks if the path is a simple, related path.
         if path_buf.components().any(|c| !matches!(c, Component::Normal(_))) {
             return Err(new_errno_error(Errno::EINVAL));
         }

         self.insert_new_fd(dir_fd, |config| match config {
             FdConfig::InputDir(dir) => {
                 let file = open_readonly_at(dir.as_fd(), &path_buf).map_err(new_errno_error)?;

                 let metadata_path_buf = get_fsverity_metadata_path(&path_buf);
                 let metadata = open_readonly_at(dir.as_fd(), &metadata_path_buf)
                     .ok()
                     .and_then(|f| parse_fsverity_metadata(f).ok());

                 Ok((file.as_raw_fd(), FdConfig::Readonly { file, alt_metadata: metadata }))
             }
             FdConfig::OutputDir(_) => {
                 Err(new_errno_error(Errno::ENOSYS)) // TODO: Implement when needed
             }
             _ => Err(new_errno_error(Errno::ENOTDIR)),
         })
     }

     fn createFileInDirectory(&self, dir_fd: i32, basename: &str, mode: i32) -> BinderResult<i32> {
         validate_basename(basename)?;

         self.insert_new_fd(dir_fd, |config| match config {
             FdConfig::InputDir(_) => Err(new_errno_error(Errno::EACCES)),
             FdConfig::OutputDir(dir) => {
                 let mode = validate_file_mode(mode)?;
                 let new_fd = openat(
                     Some(dir.as_raw_fd()),
                     basename,
                     // This function is supposed to be only called when FUSE/authfs thinks the file
                     // does not exist. However, if the file does exist from the view of fd_server
                     // (where the execution context is considered untrusted), we prefer to honor
                     // authfs and still allow the create to success. Therefore, always use O_TRUNC.
                     OFlag::O_CREAT | OFlag::O_RDWR | OFlag::O_TRUNC,
                     mode,
                 )
                 .map_err(new_errno_error)?;
                 // SAFETY: new_fd is just created and not an error.
                 let new_file = unsafe { File::from_raw_fd(new_fd) };
                 Ok((new_fd, FdConfig::ReadWrite(new_file)))
             }
             _ => Err(new_errno_error(Errno::ENOTDIR)),
         })
     }

     fn createDirectoryInDirectory(
         &self,
         dir_fd: i32,
         basename: &str,
         mode: i32,
     ) -> BinderResult<i32> {
         validate_basename(basename)?;

         self.insert_new_fd(dir_fd, |config| match config {
             FdConfig::InputDir(_) => Err(new_errno_error(Errno::EACCES)),
             FdConfig::OutputDir(_) => {
                 let mode = validate_file_mode(mode)?;
                 mkdirat(Some(dir_fd), basename, mode).map_err(new_errno_error)?;
                 let new_dir_fd = openat(
                     Some(dir_fd),
                     basename,
                     OFlag::O_DIRECTORY | OFlag::O_RDONLY,
                     Mode::empty(),
                 )
                 .map_err(new_errno_error)?;
                 // SAFETY: new_dir_fd is just created and not an error.
                 let fd_owner = unsafe { OwnedFd::from_raw_fd(new_dir_fd) };
                 Ok((new_dir_fd, FdConfig::OutputDir(fd_owner)))
             }
             _ => Err(new_errno_error(Errno::ENOTDIR)),
         })
     }

     fn deleteFile(&self, dir_fd: i32, basename: &str) -> BinderResult<()> {
         validate_basename(basename)?;

         self.handle_fd(dir_fd, |config| match config {
             FdConfig::OutputDir(_) => {
                 unlinkat(Some(dir_fd), basename, UnlinkatFlags::NoRemoveDir)
                     .map_err(new_errno_error)?;
                 Ok(())
             }
             FdConfig::InputDir(_) => Err(new_errno_error(Errno::EACCES)),
             _ => Err(new_errno_error(Errno::ENOTDIR)),
         })
     }

     fn deleteDirectory(&self, dir_fd: i32, basename: &str) -> BinderResult<()> {
         validate_basename(basename)?;

         self.handle_fd(dir_fd, |config| match config {
             FdConfig::OutputDir(_) => {
                 unlinkat(Some(dir_fd), basename, UnlinkatFlags::RemoveDir)
                     .map_err(new_errno_error)?;
                 Ok(())
             }
             FdConfig::InputDir(_) => Err(new_errno_error(Errno::EACCES)),
             _ => Err(new_errno_error(Errno::ENOTDIR)),
         })
     }

     fn chmod(&self, fd: i32, mode: i32) -> BinderResult<()> {
         self.handle_fd(fd, |config| match config {
             FdConfig::ReadWrite(_) | FdConfig::OutputDir(_) => {
                 let mode = validate_file_mode(mode)?;
                 fchmod(fd, mode).map_err(new_errno_error)
             }
             _ => Err(new_errno_error(Errno::EACCES)),
         })
     }

     fn statfs(&self) -> BinderResult<FsStat> {
         let st = statvfs("/data").map_err(new_errno_error)?;
         try_into_fs_stat(st).map_err(|_e| new_errno_error(Errno::EINVAL))
     }
 }

 // FFI types like `c_long` vary on 32/64-bit, and the check is only needed on
 // 64-bit conversions. Fixing this lint makes the code less readable.
 #[allow(unknown_lints)]
 #[allow(clippy::unnecessary_fallible_conversions)]
 fn try_into_fs_stat(st: Statvfs) -> Result<FsStat, std::num::TryFromIntError> {
     Ok(FsStat {
         blockSize: st.block_size().try_into()?,
         fragmentSize: st.fragment_size().try_into()?,
         blockNumbers: st.blocks().try_into()?,
         blockAvailable: st.blocks_available().try_into()?,
         inodesAvailable: st.files_available().try_into()?,
         maxFilename: st.name_max().try_into()?,
     })
 }

 fn read_into_buf(file: &File, max_size: usize, offset: u64) -> io::Result<Vec<u8>> {
     let remaining = file.metadata()?.len().saturating_sub(offset);
     let buf_size = min(remaining, max_size as u64) as usize;
     let mut buf = vec![0; buf_size];
     file.read_exact_at(&mut buf, offset)?;
     Ok(buf)
 }

 fn new_errno_error(errno: Errno) -> Status {
     Status::new_service_specific_error_str(errno as i32, Some(errno.desc()))
 }

 fn open_readonly_at(dir_fd: BorrowedFd, path: &Path) -> nix::Result<File> {
     let new_fd = openat(Some(dir_fd.as_raw_fd()), path, OFlag::O_RDONLY, Mode::empty())?;
     // SAFETY: new_fd is just created successfully and not owned.
     let new_file = unsafe { File::from_raw_fd(new_fd) };
     Ok(new_file)
 }

 fn validate_and_cast_offset(offset: i64) -> Result<u64, Status> {
     offset.try_into().map_err(|_| new_errno_error(Errno::EINVAL))
 }

 fn validate_and_cast_size(size: i32) -> Result<usize, Status> {
     if size > MAX_REQUESTING_DATA {
         Err(new_errno_error(Errno::EFBIG))
     } else {
         size.try_into().map_err(|_| new_errno_error(Errno::EINVAL))
     }
 }

 fn validate_basename(name: &str) -> BinderResult<()> {
     if name.contains(MAIN_SEPARATOR) {
         Err(new_errno_error(Errno::EINVAL))
     } else {
         Ok(())
     }
 }

 fn validate_file_mode(mode: i32) -> BinderResult<Mode> {
     let mode = Mode::from_bits(mode as mode_t).ok_or_else(|| new_errno_error(Errno::EINVAL))?;
     if mode.intersects(FORBIDDEN_MODES) {
         Err(new_errno_error(Errno::EPERM))
     } else {
         Ok(mode)
     }
 }
	/*
	* Copyright (C) 2021 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 anyhow::Result;
	use log::error;
	use nix::{
	errno::Errno, fcntl::openat, fcntl::OFlag, sys::stat::fchmod, sys::stat::mkdirat,
	sys::stat::mode_t, sys::stat::Mode, sys::statvfs::statvfs, sys::statvfs::Statvfs,
	unistd::unlinkat, unistd::UnlinkatFlags,
	};
	use std::cmp::min;
	use std::collections::{btree_map, BTreeMap};
	use std::convert::TryInto;
	use std::fs::File;
	use std::io;
	use std::os::unix::fs::FileExt;
	use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, OwnedFd};
	use std::path::{Component, Path, PathBuf, MAIN_SEPARATOR};
	use std::sync::{Arc, RwLock};

	use authfs_aidl_interface::aidl::com::android::virt::fs::IVirtFdService::{
	BnVirtFdService, FsStat::FsStat, IVirtFdService, MAX_REQUESTING_DATA,
	};
	use authfs_fsverity_metadata::{
	get_fsverity_metadata_path, parse_fsverity_metadata, FSVerityMetadata,
	};
	use binder::{
	BinderFeatures, ExceptionCode, Interface, Result as BinderResult, Status, StatusCode, Strong,
	};

	/// Bitflags of forbidden file mode, e.g. setuid, setgid and sticky bit.
	const FORBIDDEN_MODES: Mode = Mode::from_bits_truncate(!0o777);

	/// Configuration of a file descriptor to be served/exposed/shared.
	pub enum FdConfig {
	/// A read-only file to serve by this server. The file is supposed to be verifiable with the
	/// associated fs-verity metadata.
	Readonly {
	/// The file to read from. fs-verity metadata can be retrieved from this file's FD.
	file: File,

	// Alternative metadata storing merkle tree and signature.
	alt_metadata: Option<Box<FSVerityMetadata>>,
	},

	/// A readable/writable file to serve by this server. This backing file should just be a
	/// regular file and does not have any specific property.
	ReadWrite(File),

	/// A read-only directory to serve by this server.
	InputDir(OwnedFd),

	/// A writable directory to serve by this server.
	OutputDir(OwnedFd),
	}

	pub struct FdService {
	/// A pool of opened files and directories, which can be looked up by the FD number.
	fd_pool: Arc<RwLock<BTreeMap<i32, FdConfig>>>,
	}

	impl FdService {
	pub fn new_binder(fd_pool: BTreeMap<i32, FdConfig>) -> Strong<dyn IVirtFdService> {
	BnVirtFdService::new_binder(
	FdService { fd_pool: Arc::new(RwLock::new(fd_pool)) },
	BinderFeatures::default(),
	)
	}

	/// Handles the requesting file `id` with `handle_fn` if it is in the FD pool. This function
	/// returns whatever `handle_fn` returns.
	fn handle_fd<F, R>(&self, id: i32, handle_fn: F) -> BinderResult<R>
	where
	F: FnOnce(&FdConfig) -> BinderResult<R>,
	{
	let fd_pool = self.fd_pool.read().unwrap();
	let fd_config = fd_pool.get(&id).ok_or_else(\|\| new_errno_error(Errno::EBADF))?;
	handle_fn(fd_config)
	}

	/// Inserts a new FD and corresponding `FdConfig` created by `create_fn` to the FD pool, then
	/// returns the new FD number.
	fn insert_new_fd<F>(&self, fd: i32, create_fn: F) -> BinderResult<i32>
	where
	F: FnOnce(&mut FdConfig) -> BinderResult<(i32, FdConfig)>,
	{
	let mut fd_pool = self.fd_pool.write().unwrap();
	let fd_config = fd_pool.get_mut(&fd).ok_or_else(\|\| new_errno_error(Errno::EBADF))?;
	let (new_fd, new_fd_config) = create_fn(fd_config)?;
	if let btree_map::Entry::Vacant(entry) = fd_pool.entry(new_fd) {
	entry.insert(new_fd_config);
	Ok(new_fd)
	} else {
	Err(Status::new_exception_str(
	ExceptionCode::ILLEGAL_STATE,
	Some(format!(
	"The newly created FD {} is already in the pool unexpectedly",
	new_fd
	)),
	))
	}
	}
	}

	impl Interface for FdService {}

	impl IVirtFdService for FdService {
	fn readFile(&self, id: i32, offset: i64, size: i32) -> BinderResult<Vec<u8>> {
	let size: usize = validate_and_cast_size(size)?;
	let offset: u64 = validate_and_cast_offset(offset)?;

	self.handle_fd(id, \|config\| match config {
	FdConfig::Readonly { file, .. } \| FdConfig::ReadWrite(file) => {
	read_into_buf(file, size, offset).map_err(\|e\| {
	error!("readFile: read error: {}", e);
	new_errno_error(Errno::EIO)
	})
	}
	FdConfig::InputDir(_) \| FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
	})
	}

	fn readFsverityMerkleTree(&self, id: i32, offset: i64, size: i32) -> BinderResult<Vec<u8>> {
	let size: usize = validate_and_cast_size(size)?;
	let offset: u64 = validate_and_cast_offset(offset)?;

	self.handle_fd(id, \|config\| match config {
	FdConfig::Readonly { file, alt_metadata, .. } => {
	let mut buf = vec![0; size];

	let s = if let Some(metadata) = &alt_metadata {
	metadata.read_merkle_tree(offset, &mut buf).map_err(\|e\| {
	error!("readFsverityMerkleTree: read error: {}", e);
	new_errno_error(Errno::EIO)
	})?
	} else {
	fsverity::read_merkle_tree(file.as_raw_fd(), offset, &mut buf).map_err(\|e\| {
	error!("readFsverityMerkleTree: failed to retrieve merkle tree: {}", e);
	new_errno_error(Errno::EIO)
	})?
	};
	debug_assert!(s <= buf.len(), "Shouldn't return more bytes than asked");
	buf.truncate(s);
	Ok(buf)
	}
	FdConfig::ReadWrite(_file) => {
	// For a writable file, Merkle tree is not expected to be served since Auth FS
	// doesn't trust it anyway. Auth FS may keep the Merkle tree privately for its own
	// use.
	Err(new_errno_error(Errno::ENOSYS))
	}
	FdConfig::InputDir(_) \| FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
	})
	}

	fn readFsveritySignature(&self, id: i32) -> BinderResult<Vec<u8>> {
	self.handle_fd(id, \|config\| match config {
	FdConfig::Readonly { file, alt_metadata, .. } => {
	if let Some(metadata) = &alt_metadata {
	if let Some(signature) = &metadata.signature {
	Ok(signature.clone())
	} else {
	Err(Status::new_service_specific_error_str(
	-1,
	Some("metadata doesn't contain a signature"),
	))
	}
	} else {
	let mut buf = vec![0; MAX_REQUESTING_DATA as usize];
	let s = fsverity::read_signature(file.as_raw_fd(), &mut buf).map_err(\|e\| {
	error!("readFsverityMerkleTree: failed to retrieve merkle tree: {}", e);
	new_errno_error(Errno::EIO)
	})?;
	debug_assert!(s <= buf.len(), "Shouldn't return more bytes than asked");
	buf.truncate(s);
	Ok(buf)
	}
	}
	FdConfig::ReadWrite(_file) => {
	// There is no signature for a writable file.
	Err(new_errno_error(Errno::ENOSYS))
	}
	FdConfig::InputDir(_) \| FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
	})
	}

	fn writeFile(&self, id: i32, buf: &[u8], offset: i64) -> BinderResult<i32> {
	self.handle_fd(id, \|config\| match config {
	FdConfig::Readonly { .. } => Err(StatusCode::INVALID_OPERATION.into()),
	FdConfig::ReadWrite(file) => {
	let offset: u64 = offset.try_into().map_err(\|_\| new_errno_error(Errno::EINVAL))?;
	// Check buffer size just to make `as i32` safe below.
	if buf.len() > i32::MAX as usize {
	return Err(new_errno_error(Errno::EOVERFLOW));
	}
	Ok(file.write_at(buf, offset).map_err(\|e\| {
	error!("writeFile: write error: {}", e);
	new_errno_error(Errno::EIO)
	})? as i32)
	}
	FdConfig::InputDir(_) \| FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
	})
	}

	fn resize(&self, id: i32, size: i64) -> BinderResult<()> {
	self.handle_fd(id, \|config\| match config {
	FdConfig::Readonly { .. } => Err(StatusCode::INVALID_OPERATION.into()),
	FdConfig::ReadWrite(file) => {
	if size < 0 {
	return Err(new_errno_error(Errno::EINVAL));
	}
	file.set_len(size as u64).map_err(\|e\| {
	error!("resize: set_len error: {}", e);
	new_errno_error(Errno::EIO)
	})
	}
	FdConfig::InputDir(_) \| FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
	})
	}

	fn getFileSize(&self, id: i32) -> BinderResult<i64> {
	self.handle_fd(id, \|config\| match config {
	FdConfig::Readonly { file, .. } => {
	let size = file
	.metadata()
	.map_err(\|e\| {
	error!("getFileSize error: {}", e);
	new_errno_error(Errno::EIO)
	})?
	.len();
	Ok(size.try_into().map_err(\|e\| {
	error!("getFileSize: File too large: {}", e);
	new_errno_error(Errno::EFBIG)
	})?)
	}
	FdConfig::ReadWrite(_file) => {
	// Content and metadata of a writable file needs to be tracked by authfs, since
	// fd_server isn't considered trusted. So there is no point to support getFileSize
	// for a writable file.
	Err(new_errno_error(Errno::ENOSYS))
	}
	FdConfig::InputDir(_) \| FdConfig::OutputDir(_) => Err(new_errno_error(Errno::EISDIR)),
	})
	}

	fn openFileInDirectory(&self, dir_fd: i32, file_path: &str) -> BinderResult<i32> {
	let path_buf = PathBuf::from(file_path);
	// Checks if the path is a simple, related path.
	if path_buf.components().any(\|c\| !matches!(c, Component::Normal(_))) {
	return Err(new_errno_error(Errno::EINVAL));
	}

	self.insert_new_fd(dir_fd, \|config\| match config {
	FdConfig::InputDir(dir) => {
	let file = open_readonly_at(dir.as_fd(), &path_buf).map_err(new_errno_error)?;

	let metadata_path_buf = get_fsverity_metadata_path(&path_buf);
	let metadata = open_readonly_at(dir.as_fd(), &metadata_path_buf)
	.ok()
	.and_then(\|f\| parse_fsverity_metadata(f).ok());

	Ok((file.as_raw_fd(), FdConfig::Readonly { file, alt_metadata: metadata }))
	}
	FdConfig::OutputDir(_) => {
	Err(new_errno_error(Errno::ENOSYS)) // TODO: Implement when needed
	}
	_ => Err(new_errno_error(Errno::ENOTDIR)),
	})
	}

	fn createFileInDirectory(&self, dir_fd: i32, basename: &str, mode: i32) -> BinderResult<i32> {
	validate_basename(basename)?;

	self.insert_new_fd(dir_fd, \|config\| match config {
	FdConfig::InputDir(_) => Err(new_errno_error(Errno::EACCES)),
	FdConfig::OutputDir(dir) => {
	let mode = validate_file_mode(mode)?;
	let new_fd = openat(
	Some(dir.as_raw_fd()),
	basename,
	// This function is supposed to be only called when FUSE/authfs thinks the file
	// does not exist. However, if the file does exist from the view of fd_server
	// (where the execution context is considered untrusted), we prefer to honor
	// authfs and still allow the create to success. Therefore, always use O_TRUNC.
	OFlag::O_CREAT \| OFlag::O_RDWR \| OFlag::O_TRUNC,
	mode,
	)
	.map_err(new_errno_error)?;
	// SAFETY: new_fd is just created and not an error.
	let new_file = unsafe { File::from_raw_fd(new_fd) };
	Ok((new_fd, FdConfig::ReadWrite(new_file)))
	}
	_ => Err(new_errno_error(Errno::ENOTDIR)),
	})
	}

	fn createDirectoryInDirectory(
	&self,
	dir_fd: i32,
	basename: &str,
	mode: i32,
	) -> BinderResult<i32> {
	validate_basename(basename)?;

	self.insert_new_fd(dir_fd, \|config\| match config {
	FdConfig::InputDir(_) => Err(new_errno_error(Errno::EACCES)),
	FdConfig::OutputDir(_) => {
	let mode = validate_file_mode(mode)?;
	mkdirat(Some(dir_fd), basename, mode).map_err(new_errno_error)?;
	let new_dir_fd = openat(
	Some(dir_fd),
	basename,
	OFlag::O_DIRECTORY \| OFlag::O_RDONLY,
	Mode::empty(),
	)
	.map_err(new_errno_error)?;
	// SAFETY: new_dir_fd is just created and not an error.
	let fd_owner = unsafe { OwnedFd::from_raw_fd(new_dir_fd) };
	Ok((new_dir_fd, FdConfig::OutputDir(fd_owner)))
	}
	_ => Err(new_errno_error(Errno::ENOTDIR)),
	})
	}

	fn deleteFile(&self, dir_fd: i32, basename: &str) -> BinderResult<()> {
	validate_basename(basename)?;

	self.handle_fd(dir_fd, \|config\| match config {
	FdConfig::OutputDir(_) => {
	unlinkat(Some(dir_fd), basename, UnlinkatFlags::NoRemoveDir)
	.map_err(new_errno_error)?;
	Ok(())
	}
	FdConfig::InputDir(_) => Err(new_errno_error(Errno::EACCES)),
	_ => Err(new_errno_error(Errno::ENOTDIR)),
	})
	}

	fn deleteDirectory(&self, dir_fd: i32, basename: &str) -> BinderResult<()> {
	validate_basename(basename)?;

	self.handle_fd(dir_fd, \|config\| match config {
	FdConfig::OutputDir(_) => {
	unlinkat(Some(dir_fd), basename, UnlinkatFlags::RemoveDir)
	.map_err(new_errno_error)?;
	Ok(())
	}
	FdConfig::InputDir(_) => Err(new_errno_error(Errno::EACCES)),
	_ => Err(new_errno_error(Errno::ENOTDIR)),
	})
	}

	fn chmod(&self, fd: i32, mode: i32) -> BinderResult<()> {
	self.handle_fd(fd, \|config\| match config {
	FdConfig::ReadWrite(_) \| FdConfig::OutputDir(_) => {
	let mode = validate_file_mode(mode)?;
	fchmod(fd, mode).map_err(new_errno_error)
	}
	_ => Err(new_errno_error(Errno::EACCES)),
	})
	}

	fn statfs(&self) -> BinderResult<FsStat> {
	let st = statvfs("/data").map_err(new_errno_error)?;
	try_into_fs_stat(st).map_err(\|_e\| new_errno_error(Errno::EINVAL))
	}
	}

	// FFI types like `c_long` vary on 32/64-bit, and the check is only needed on
	// 64-bit conversions. Fixing this lint makes the code less readable.
	#[allow(unknown_lints)]
	#[allow(clippy::unnecessary_fallible_conversions)]
	fn try_into_fs_stat(st: Statvfs) -> Result<FsStat, std::num::TryFromIntError> {
	Ok(FsStat {
	blockSize: st.block_size().try_into()?,
	fragmentSize: st.fragment_size().try_into()?,
	blockNumbers: st.blocks().try_into()?,
	blockAvailable: st.blocks_available().try_into()?,
	inodesAvailable: st.files_available().try_into()?,
	maxFilename: st.name_max().try_into()?,
	})
	}

	fn read_into_buf(file: &File, max_size: usize, offset: u64) -> io::Result<Vec<u8>> {
	let remaining = file.metadata()?.len().saturating_sub(offset);
	let buf_size = min(remaining, max_size as u64) as usize;
	let mut buf = vec![0; buf_size];
	file.read_exact_at(&mut buf, offset)?;
	Ok(buf)
	}

	fn new_errno_error(errno: Errno) -> Status {
	Status::new_service_specific_error_str(errno as i32, Some(errno.desc()))
	}

	fn open_readonly_at(dir_fd: BorrowedFd, path: &Path) -> nix::Result<File> {
	let new_fd = openat(Some(dir_fd.as_raw_fd()), path, OFlag::O_RDONLY, Mode::empty())?;
	// SAFETY: new_fd is just created successfully and not owned.
	let new_file = unsafe { File::from_raw_fd(new_fd) };
	Ok(new_file)
	}

	fn validate_and_cast_offset(offset: i64) -> Result<u64, Status> {
	offset.try_into().map_err(\|_\| new_errno_error(Errno::EINVAL))
	}

	fn validate_and_cast_size(size: i32) -> Result<usize, Status> {
	if size > MAX_REQUESTING_DATA {
	Err(new_errno_error(Errno::EFBIG))
	} else {
	size.try_into().map_err(\|_\| new_errno_error(Errno::EINVAL))
	}
	}

	fn validate_basename(name: &str) -> BinderResult<()> {
	if name.contains(MAIN_SEPARATOR) {
	Err(new_errno_error(Errno::EINVAL))
	} else {
	Ok(())
	}
	}

	fn validate_file_mode(mode: i32) -> BinderResult<Mode> {
	let mode = Mode::from_bits(mode as mode_t).ok_or_else(\|\| new_errno_error(Errno::EINVAL))?;
	if mode.intersects(FORBIDDEN_MODES) {
	Err(new_errno_error(Errno::EPERM))
	} else {
	Ok(mode)
	}
	}