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Fix GL X11 error handling (#181)

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This PR fixes a soundness issue inside the `XErrorHandler` utility function, which could use an xlib `Display` pointer that had no guarantee to be still valid.

This could happen because the underlying `XErrorEvent` was stored directly inside the returned error type, and the `Display` pointer it contained was only called to extract the error message during in `Debug` implementation, which could happen long after the associated `Display` had been destroyed.

This PR fixes this by extracting the error message upfront and storing it as a string as soon as the error happens.
This PR also fixes the `handle` method that was not properly marked `unsafe`.
This commit is contained in:
Adrien Prokopowicz 2024-03-29 04:41:40 +01:00 committed by GitHub
parent f5b0c6d460
commit bcbdb8921f
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GPG key ID: B5690EEEBB952194
2 changed files with 77 additions and 33 deletions
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10
src/gl/x11.rs
View file

@ -229,12 +229,12 @@ impl GlContext {
}
pub fn swap_buffers(&self) {
errors::XErrorHandler::handle(self.display, |error_handler| {
unsafe {
unsafe {
errors::XErrorHandler::handle(self.display, |error_handler| {
glx::glXSwapBuffers(self.display, self.window);
}
error_handler.check().unwrap();
})
error_handler.check().unwrap();
})
}
}
}

100
src/gl/x11/errors.rs
View file

@ -1,25 +1,27 @@
use std::ffi::CStr;
use std::fmt::{Debug, Formatter};
use std::fmt::{Debug, Display, Formatter};
use x11::xlib;
use std::cell::RefCell;
use std::error::Error;
use std::os::raw::{c_int, c_uchar, c_ulong};
use std::panic::AssertUnwindSafe;
thread_local! {
/// Used as part of [`XerrorHandler::handle()`]. When an X11 error occurs during this function,
/// Used as part of [`XErrorHandler::handle()`]. When an X11 error occurs during this function,
/// the error gets copied to this RefCell after which the program is allowed to resume. The
/// error can then be converted to a regular Rust Result value afterwards.
static CURRENT_X11_ERROR: RefCell<Option<xlib::XErrorEvent>> = RefCell::new(None);
/// error can then be converted to a regular Rust Result value afterward.
static CURRENT_X11_ERROR: RefCell<Option<XLibError>> = const { RefCell::new(None) };
}
/// A helper struct for safe X11 error handling
pub struct XErrorHandler<'a> {
display: *mut xlib::Display,
error: &'a RefCell<Option<xlib::XErrorEvent>>,
error: &'a RefCell<Option<XLibError>>,
}
impl<'a> XErrorHandler<'a> {
/// Syncs and checks if any previous X11 calls returned an error
/// Syncs and checks if any previous X11 calls from the given display returned an error
pub fn check(&mut self) -> Result<(), XLibError> {
// Flush all possible previous errors
unsafe {
@ -29,20 +31,27 @@ impl<'a> XErrorHandler<'a> {
match error {
None => Ok(()),
Some(inner) => Err(XLibError { inner }),
Some(inner) => Err(inner),
}
}
/// Sets up a temporary X11 error handler for the duration of the given closure, and allows
/// that closure to check on the latest X11 error at any time
pub fn handle<T, F: FnOnce(&mut XErrorHandler) -> T>(
/// that closure to check on the latest X11 error at any time.
///
/// # Safety
///
/// The given display pointer *must* be and remain valid for the duration of this function, as
/// well as for the duration of the given `handler` closure.
pub unsafe fn handle<T, F: FnOnce(&mut XErrorHandler) -> T>(
display: *mut xlib::Display, handler: F,
) -> T {
/// # Safety
/// The given display and error pointers *must* be valid for the duration of this function.
unsafe extern "C" fn error_handler(
_dpy: *mut xlib::Display, err: *mut xlib::XErrorEvent,
) -> i32 {
// SAFETY: the error pointer should be safe to copy
let err = *err;
// SAFETY: the error pointer should be safe to access
let err = &*err;
CURRENT_X11_ERROR.with(|error| {
let mut error = error.borrow_mut();
@ -51,7 +60,7 @@ impl<'a> XErrorHandler<'a> {
// cause of the other errors
Some(_) => 1,
None => {
*error = Some(err);
*error = Some(XLibError::from_event(err));
0
}
}
@ -65,7 +74,9 @@ impl<'a> XErrorHandler<'a> {
CURRENT_X11_ERROR.with(|error| {
// Make sure to clear any errors from the last call to this function
*error.borrow_mut() = None;
{
*error.borrow_mut() = None;
}
let old_handler = unsafe { xlib::XSetErrorHandler(Some(error_handler)) };
let panic_result = std::panic::catch_unwind(AssertUnwindSafe(|| {
@ -84,15 +95,41 @@ impl<'a> XErrorHandler<'a> {
}
pub struct XLibError {
inner: xlib::XErrorEvent,
type_: c_int,
resourceid: xlib::XID,
serial: c_ulong,
error_code: c_uchar,
request_code: c_uchar,
minor_code: c_uchar,
display_name: Box<str>,
}
impl XLibError {
pub fn get_display_name(&self, buf: &mut [u8]) -> &CStr {
/// # Safety
/// The display pointer inside error must be valid for the duration of this call
unsafe fn from_event(error: &xlib::XErrorEvent) -> Self {
Self {
type_: error.type_,
resourceid: error.resourceid,
serial: error.serial,
error_code: error.error_code,
request_code: error.request_code,
minor_code: error.minor_code,
display_name: Self::get_display_name(error),
}
}
/// # Safety
/// The display pointer inside error must be valid for the duration of this call
unsafe fn get_display_name(error: &xlib::XErrorEvent) -> Box<str> {
let mut buf = [0; 255];
unsafe {
xlib::XGetErrorText(
self.inner.display,
self.inner.error_code.into(),
error.display,
error.error_code.into(),
buf.as_mut_ptr().cast(),
(buf.len() - 1) as i32,
);
@ -100,23 +137,30 @@ impl XLibError {
*buf.last_mut().unwrap() = 0;
// SAFETY: whatever XGetErrorText did or not, we guaranteed there is a nul byte at the end of the buffer
unsafe { CStr::from_ptr(buf.as_mut_ptr().cast()) }
let cstr = unsafe { CStr::from_ptr(buf.as_mut_ptr().cast()) };
cstr.to_string_lossy().into()
}
}
impl Debug for XLibError {
fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
let mut buf = [0; 255];
let display_name = self.get_display_name(&mut buf).to_string_lossy();
f.debug_struct("XLibError")
.field("error_code", &self.inner.error_code)
.field("error_message", &display_name)
.field("minor_code", &self.inner.minor_code)
.field("request_code", &self.inner.request_code)
.field("type", &self.inner.type_)
.field("resource_id", &self.inner.resourceid)
.field("serial", &self.inner.serial)
.field("error_code", &self.error_code)
.field("error_message", &self.display_name)
.field("minor_code", &self.minor_code)
.field("request_code", &self.request_code)
.field("type", &self.type_)
.field("resource_id", &self.resourceid)
.field("serial", &self.serial)
.finish()
}
}
impl Display for XLibError {
fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
write!(f, "XLib error: {} (error code {})", &self.display_name, self.error_code)
}
}
impl Error for XLibError {}