virtio/fs/worker.rs

// Copyright 2019 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use std::convert::TryFrom;
use std::convert::TryInto;
use std::fs::File;
use std::io;
use std::os::unix::io::AsRawFd;
use std::sync::Arc;

use base::error;
use base::syscall;
use base::Event;
use base::EventToken;
use base::Protection;
use base::SafeDescriptor;
use base::Tube;
use base::WaitContext;
use fuse::filesystem::FileSystem;
use fuse::filesystem::ZeroCopyReader;
use fuse::filesystem::ZeroCopyWriter;
use sync::Mutex;
use vm_control::FsMappingRequest;
use vm_control::VmResponse;

use crate::virtio::fs::Error;
use crate::virtio::fs::Result;
use crate::virtio::Queue;
use crate::virtio::Reader;
use crate::virtio::Writer;

impl fuse::Reader for Reader {}

impl fuse::Writer for Writer {
    type ClosureWriter = Self;

    fn write_at<F>(&mut self, offset: usize, f: F) -> io::Result<usize>
    where
        F: Fn(&mut Self) -> io::Result<usize>,
    {
        let mut writer = Writer::split_at(self, offset);
        f(&mut writer)
    }

    fn has_sufficient_buffer(&self, size: u32) -> bool {
        self.available_bytes() >= size as usize
    }
}

impl ZeroCopyReader for Reader {
    fn read_to(&mut self, f: &mut File, count: usize, off: u64) -> io::Result<usize> {
        self.read_to_at(f, count, off)
    }
}

impl ZeroCopyWriter for Writer {
    fn write_from(&mut self, f: &mut File, count: usize, off: u64) -> io::Result<usize> {
        self.write_from_at(f, count, off)
    }
}

struct Mapper {
    tube: Arc<Mutex<Tube>>,
    slot: u32,
}

impl Mapper {
    fn new(tube: Arc<Mutex<Tube>>, slot: u32) -> Self {
        Self { tube, slot }
    }

    fn process_request(&self, request: &FsMappingRequest) -> io::Result<()> {
        let tube = self.tube.lock();

        tube.send(request).map_err(|e| {
            error!("failed to send request {:?}: {}", request, e);
            io::Error::from_raw_os_error(libc::EINVAL)
        })?;

        match tube.recv() {
            Ok(VmResponse::Ok) => Ok(()),
            Ok(VmResponse::Err(e)) => Err(e.into()),
            r => {
                error!("failed to process {:?}: {:?}", request, r);
                Err(io::Error::from_raw_os_error(libc::EIO))
            }
        }
    }
}

impl fuse::Mapper for Mapper {
    fn map(
        &self,
        mem_offset: u64,
        size: usize,
        fd: &dyn AsRawFd,
        file_offset: u64,
        prot: Protection,
    ) -> io::Result<()> {
        let mem_offset: usize = mem_offset.try_into().map_err(|e| {
            error!("mem_offset {} is too big: {}", mem_offset, e);
            io::Error::from_raw_os_error(libc::EINVAL)
        })?;

        let fd = SafeDescriptor::try_from(fd)?;

        let request = FsMappingRequest::CreateMemoryMapping {
            slot: self.slot,
            fd,
            size,
            file_offset,
            prot,
            mem_offset,
        };

        self.process_request(&request)
    }

    fn unmap(&self, offset: u64, size: u64) -> io::Result<()> {
        let offset: usize = offset.try_into().map_err(|e| {
            error!("offset {} is too big: {}", offset, e);
            io::Error::from_raw_os_error(libc::EINVAL)
        })?;
        let size: usize = size.try_into().map_err(|e| {
            error!("size {} is too big: {}", size, e);
            io::Error::from_raw_os_error(libc::EINVAL)
        })?;

        let request = FsMappingRequest::RemoveMemoryMapping {
            slot: self.slot,
            offset,
            size,
        };

        self.process_request(&request)
    }
}

pub struct Worker<F: FileSystem + Sync> {
    pub(crate) queue: Queue,
    server: Arc<fuse::Server<F>>,
    tube: Arc<Mutex<Tube>>,
    slot: u32,
}

fn process_fs_queue<F: FileSystem + Sync>(
    queue: &mut Queue,
    server: &Arc<fuse::Server<F>>,
    tube: &Arc<Mutex<Tube>>,
    slot: u32,
) -> Result<()> {
    let mapper = Mapper::new(Arc::clone(tube), slot);
    while let Some(mut avail_desc) = queue.pop() {
        let total =
            server.handle_message(&mut avail_desc.reader, &mut avail_desc.writer, &mapper)?;

        queue.add_used(avail_desc, total as u32);
        queue.trigger_interrupt();
    }

    Ok(())
}

impl<F: FileSystem + Sync> Worker<F> {
    pub fn new(
        queue: Queue,
        server: Arc<fuse::Server<F>>,
        tube: Arc<Mutex<Tube>>,
        slot: u32,
    ) -> Worker<F> {
        Worker {
            queue,
            server,
            tube,
            slot,
        }
    }

    pub fn run(&mut self, kill_evt: Event) -> Result<()> {
        let mut ruid: libc::uid_t = 0;
        let mut euid: libc::uid_t = 0;
        let mut suid: libc::uid_t = 0;
        // SAFETY: Safe because this doesn't modify any memory and we check the return value.
        syscall!(unsafe { libc::getresuid(&mut ruid, &mut euid, &mut suid) })
            .map_err(Error::GetResuid)?;

        // Only need to set SECBIT_NO_SETUID_FIXUP for threads which could change uid.
        if ruid == 0 || ruid != euid || ruid != suid {
            // We need to set the no setuid fixup secure bit so that we don't drop capabilities when
            // changing the thread uid/gid. Without this, creating new entries can fail in some
            // corner cases.
            const SECBIT_NO_SETUID_FIXUP: i32 = 1 << 2;

            let mut securebits = syscall!(
                // SAFETY:
                // Safe because this doesn't modify any memory and we check the return value.
                unsafe { libc::prctl(libc::PR_GET_SECUREBITS) }
            )
            .map_err(Error::GetSecurebits)?;

            securebits |= SECBIT_NO_SETUID_FIXUP;

            syscall!(
                // SAFETY:
                // Safe because this doesn't modify any memory and we check the return value.
                unsafe { libc::prctl(libc::PR_SET_SECUREBITS, securebits) }
            )
            .map_err(Error::SetSecurebits)?;
        }

        // To avoid extra locking, unshare filesystem attributes from parent. This includes the
        // current working directory and umask.
        syscall!(
            // SAFETY: Safe because this doesn't modify any memory and we check the return value.
            unsafe { libc::unshare(libc::CLONE_FS) }
        )
        .map_err(Error::UnshareFromParent)?;

        #[derive(EventToken)]
        enum Token {
            // A request is ready on the queue.
            QueueReady,
            // The parent thread requested an exit.
            Kill,
        }

        let wait_ctx = WaitContext::build_with(&[
            (self.queue.event(), Token::QueueReady),
            (&kill_evt, Token::Kill),
        ])
        .map_err(Error::CreateWaitContext)?;

        loop {
            let events = wait_ctx.wait().map_err(Error::WaitError)?;
            for event in events.iter().filter(|e| e.is_readable) {
                match event.token {
                    Token::QueueReady => {
                        self.queue.event().wait().map_err(Error::ReadQueueEvent)?;
                        if let Err(e) =
                            process_fs_queue(&mut self.queue, &self.server, &self.tube, self.slot)
                        {
                            error!("virtio-fs transport error: {}", e);
                            return Err(e);
                        }
                    }
                    Token::Kill => return Ok(()),
                }
            }
        }
    }
}