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vmm: dup serial fds to preserve them across reboots

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During vm_shutdown or vm_snapshot, all the console devices will be
closed. When this happens stdout (FD #2) will also be closed as the
console device using these FD is closed. If the VM were to be started
later, FD#2 can be assigned to a different file. But
pre_create_console_devices looks for FD#2 while opening tty device,
which could point to any file.

To avoid this problem, the STDOUT FD is duplicated when being
assigned to a console device. Even if the console devices were to be
closed, the duplicated FD will be closed and FD#2 will continue to
point to STDOUT.

Signed-off-by: Praveen K Paladugu <prapal@linux.microsoft.com>
This commit is contained in:
Praveen K Paladugu 2024-05-16 20:41:35 +00:00 committed by Rob Bradford
parent dc723171a7
commit a8fa2af64b
1 changed files with 31 additions and 3 deletions
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34
vmm/src/console_devices.rs
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@ -237,9 +237,37 @@ pub(crate) fn pre_create_console_devices(vmm: &mut Vmm) -> ConsoleDeviceResult<C
vmconfig.serial.file = Some(path.clone());
}
ConsoleOutputMode::Tty => {
let out = stdout();
console_info.serial_main_fd = Some(out.as_raw_fd());
set_raw_mode(&out, vmm.original_termios_opt.clone())?;
// During vm_shutdown, when serial device is closed, FD#2(STDOUT)
// will be closed and FD#2 could be reused in a future boot of the
// guest by a different file.
//
// To ensure FD#2 always points to STANDARD OUT, a `dup` of STDOUT
// is passed to serial device. Doing so, even if the serial device
// were to be closed, FD#2 will continue to point to STANDARD OUT.
// SAFETY: FFI call to dup. Trivially safe.
let stdout = unsafe { libc::dup(libc::STDOUT_FILENO) };
if stdout == -1 {
return vmm_sys_util::errno::errno_result().map_err(ConsoleDeviceError::DupFd);
}
// SAFETY: stdout is valid and owned solely by us.
let stdout = unsafe { File::from_raw_fd(stdout) };
// SAFETY: FFI call. Trivially safe.
if unsafe { libc::isatty(libc::STDOUT_FILENO) } == 1 {
vmm.console_resize_pipe = Some(
listen_for_sigwinch_on_tty(
stdout.try_clone().unwrap(),
&vmm.seccomp_action,
vmm.hypervisor.hypervisor_type(),
)
.map_err(ConsoleDeviceError::StartSigwinchListener)?,
);
}
// Make sure stdout is in raw mode, if it's a terminal.
set_raw_mode(&stdout, vmm.original_termios_opt.clone())?;
console_info.serial_main_fd = Some(stdout.into_raw_fd());
}
ConsoleOutputMode::Socket => {
let listener = UnixListener::bind(vmconfig.serial.socket.as_ref().unwrap())