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vmm: fix console IO safety

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Rebooting a VM fails with the following error when debug assertions
are enabled:

	fatal runtime error: IO Safety violation: owned file descriptor already closed

This happens because FromRawFd::from_raw_fd is used on RawFds stored
in ConsoleInfo every time a VM begins to boot, so the second
time (after a reboot, or if the first attempt to boot via the API
failed), the fd will be closed.  Until this assertion is hit, the code
is operating on either closed file descriptors, or new file
descriptors for something completely different.  If debug assertions
are disabled, it will just continue doing this with unpredictable
results.

To fix this, and prevent the problem reocurring, ownership of the
console file descriptors needs to be properly tracked, using Rust's
type system, so this commit refactors the console code to do that.
The file descriptors are now passed around with reference counts, so
they won't be closed prematurely.  The obvious way to do this would be
to just have each member of ConsoleInfo be an Arc<File>, but we need
to accomodate that serial console file descriptors can also be
sockets.  We can't just store an OwnedFd and convert it when it's
used, because we only get a reference from the Arc, so we need to
store the descriptors as their concrete types in an enum.  Since this
basically duplicates the ConsoleOutputMode enum from the config, the
ConsoleOutputMode enum is now not used past constructing the
ConsoleInfo.

So that ownership can be represented consistently, the debug console's
tty mode now uses its own stdout descriptor.

I'm still using .try_clone().unwrap() (i.e. dup()) to clone file
descriptors for Endpoint::FilePair and Endpoint::TtyPair, because I
assume there's a reason for them not just to hold a single file
descriptor.

I've also retained the existing behaviour of having serial manager
ignore the tty file descriptor passed to it (which is stdout), and
instead using stdin.  It looks a lot weirder now, because it has to
explicitly indicate it's ignoring the fd with an underscore binding.

Fixes: 52eebaf6 ("vmm: refactor DeviceManager to use console_info")
Signed-off-by: Alyssa Ross <hi@alyssa.is>
This commit is contained in:
Alyssa Ross
2024-09-20 21:14:02 +02:00
committed by Rob Bradford
parent a5df86698b
commit 287887c99c
4 changed files with 213 additions and 264 deletions
Download Patch File Download Diff File Expand all files Collapse all files
vmm/src/serial_manager.rs
+34 -48
View File
@@ -3,7 +3,7 @@
// SPDX-License-Identifier: Apache-2.0
//
use crate::config::ConsoleOutputMode;
use crate::console_devices::ConsoleOutput;
#[cfg(target_arch = "aarch64")]
use devices::legacy::Pl011;
#[cfg(target_arch = "x86_64")]
@@ -13,9 +13,8 @@ use serial_buffer::SerialBuffer;
use std::fs::File;
use std::io::Read;
use std::net::Shutdown;
use std::os::fd::RawFd;
use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd};
use std::os::unix::net::{UnixListener, UnixStream};
use std::os::unix::net::UnixStream;
use std::panic::AssertUnwindSafe;
use std::path::PathBuf;
use std::sync::atomic::{AtomicBool, Ordering};
@@ -112,11 +111,10 @@ pub struct SerialManager {
#[cfg(target_arch = "aarch64")]
serial: Arc<Mutex<Pl011>>,
epoll_file: File,
in_file: File,
in_file: ConsoleOutput,
kill_evt: EventFd,
handle: Option<thread::JoinHandle<()>>,
pty_write_out: Option<Arc<AtomicBool>>,
mode: ConsoleOutputMode,
socket_path: Option<PathBuf>,
}
@@ -124,23 +122,14 @@ impl SerialManager {
pub fn new(
#[cfg(target_arch = "x86_64")] serial: Arc<Mutex<Serial>>,
#[cfg(target_arch = "aarch64")] serial: Arc<Mutex<Pl011>>,
main_fd: Option<RawFd>,
mode: ConsoleOutputMode,
mut output: ConsoleOutput,
socket: Option<PathBuf>,
) -> Result<Option<Self>> {
let mut socket_path: Option<PathBuf> = None;
let in_file = match mode {
ConsoleOutputMode::Pty => {
if let Some(pty_main) = main_fd {
// SAFETY: pty_main is guaranteed to be a valid fd from
// pre_create_console_devices() in vmm/src/console_devices.rs
unsafe { File::from_raw_fd(pty_main) }
} else {
return Ok(None);
}
}
ConsoleOutputMode::Tty => {
let in_fd = match output {
ConsoleOutput::Pty(ref fd) => fd.as_raw_fd(),
ConsoleOutput::Tty(_) => {
// If running on an interactive TTY then accept input
// SAFETY: trivially safe
if unsafe { libc::isatty(libc::STDIN_FILENO) == 1 } {
@@ -162,22 +151,17 @@ impl SerialManager {
return Err(Error::SetNonBlocking(std::io::Error::last_os_error()));
}
stdin_clone
output = ConsoleOutput::Tty(Arc::new(stdin_clone));
fd
} else {
return Ok(None);
}
}
ConsoleOutputMode::Socket => {
if let Some(socket_fd) = main_fd {
if let Some(path_in_socket) = socket {
socket_path = Some(path_in_socket.clone());
}
// SAFETY: socke_fd is guaranteed to be a valid fd from
// pre_create_console_devices() in vmm/src/console_devices.rs
unsafe { File::from_raw_fd(socket_fd) }
} else {
return Ok(None);
ConsoleOutput::Socket(ref fd) => {
if let Some(path_in_socket) = socket {
socket_path = Some(path_in_socket.clone());
}
fd.as_raw_fd()
}
_ => return Ok(None),
};
@@ -193,7 +177,7 @@ impl SerialManager {
)
.map_err(Error::Epoll)?;
let epoll_fd_data = if mode == ConsoleOutputMode::Socket {
let epoll_fd_data = if let ConsoleOutput::Socket(_) = output {
EpollDispatch::Socket
} else {
EpollDispatch::File
@@ -202,16 +186,16 @@ impl SerialManager {
epoll::ctl(
epoll_fd,
epoll::ControlOptions::EPOLL_CTL_ADD,
in_file.as_raw_fd(),
in_fd,
epoll::Event::new(epoll::Events::EPOLLIN, epoll_fd_data as u64),
)
.map_err(Error::Epoll)?;
let mut pty_write_out = None;
if mode == ConsoleOutputMode::Pty {
if let ConsoleOutput::Pty(ref file) = output {
let write_out = Arc::new(AtomicBool::new(false));
pty_write_out = Some(write_out.clone());
let writer = in_file.try_clone().map_err(Error::FileClone)?;
let writer = file.try_clone().map_err(Error::FileClone)?;
let buffer = SerialBuffer::new(Box::new(writer), write_out);
serial
.as_ref()
@@ -227,11 +211,10 @@ impl SerialManager {
Ok(Some(SerialManager {
serial,
epoll_file,
in_file,
in_file: output,
kill_evt,
handle: None,
pty_write_out,
mode,
socket_path,
}))
}
@@ -270,15 +253,10 @@ impl SerialManager {
}
let epoll_fd = self.epoll_file.as_raw_fd();
let mut in_file = self.in_file.try_clone().map_err(Error::FileClone)?;
let in_file = self.in_file.clone();
let serial = self.serial.clone();
let pty_write_out = self.pty_write_out.clone();
// SAFETY: from_raw_fd is always called with a valid fd
let listener = unsafe {
UnixListener::from_raw_fd(in_file.try_clone().map_err(Error::FileClone)?.into_raw_fd())
};
let mut reader: Option<UnixStream> = None;
let mode = self.mode.clone();
// In case of PTY, we want to be able to detect a connection on the
// other end of the PTY. This is done by detecting there's no event
@@ -314,7 +292,7 @@ impl SerialManager {
}
};
if mode != ConsoleOutputMode::Socket && num_events == 0 {
if matches!(in_file, ConsoleOutput::Socket(_)) && num_events == 0 {
// This very specific case happens when the serial is connected
// to a PTY. We know EPOLLHUP is always present when there's nothing
// connected at the other end of the PTY. That's why getting no event
@@ -338,6 +316,11 @@ impl SerialManager {
.shutdown(Shutdown::Both)
.map_err(Error::AcceptConnection)?;
}
let ConsoleOutput::Socket(ref listener) = in_file else {
unreachable!();
};
// Events on the listening socket will be connection requests.
// Accept them, create a reader and a writer.
let (unix_stream, _) =
@@ -363,8 +346,8 @@ impl SerialManager {
EpollDispatch::File => {
if event.events & libc::EPOLLIN as u32 != 0 {
let mut input = [0u8; 64];
let count = match mode {
ConsoleOutputMode::Socket => {
let count = match &in_file {
ConsoleOutput::Socket(_) => {
if let Some(mut serial_reader) = reader.as_ref() {
let count = serial_reader
.read(&mut input)
@@ -386,9 +369,12 @@ impl SerialManager {
0
}
}
_ => in_file
.read(&mut input)
.map_err(Error::ReadInput)?,
ConsoleOutput::Pty(file) | ConsoleOutput::Tty(file) => {
(&**file)
.read(&mut input)
.map_err(Error::ReadInput)?
}
_ => unreachable!(),
};
// Replace "\n" with "\r" to deal with Windows SAC (#1170)
@@ -444,7 +430,7 @@ impl Drop for SerialManager {
if let Some(handle) = self.handle.take() {
handle.join().ok();
}
if self.mode == ConsoleOutputMode::Socket {
if let ConsoleOutput::Socket(_) = self.in_file {
if let Some(socket_path) = self.socket_path.as_ref() {
std::fs::remove_file(socket_path.as_os_str())
.map_err(Error::RemoveUnixSocket)