diff --git a/src/main.rs b/src/main.rs index 8a4fce002a..16dcf102fd 100644 --- a/src/main.rs +++ b/src/main.rs @@ -39,6 +39,7 @@ extern crate vm_control; pub mod argument; pub mod linux; +pub mod panic_hook; #[cfg(feature = "plugin")] pub mod plugin; @@ -925,6 +926,8 @@ fn crosvm_main() -> std::result::Result<(), ()> { return Err(()); } + panic_hook::set_panic_hook(); + let mut args = std::env::args(); if args.next().is_none() { error!("expected executable name"); diff --git a/src/panic_hook.rs b/src/panic_hook.rs new file mode 100644 index 0000000000..d61b7d538e --- /dev/null +++ b/src/panic_hook.rs @@ -0,0 +1,105 @@ +// Copyright 2019 The Chromium OS Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +use std::env; +use std::fs::File; +use std::io::{stderr, Read}; +use std::os::unix::io::{FromRawFd, IntoRawFd}; +use std::panic::{self, PanicInfo}; +use std::process::abort; +use std::string::String; + +use libc::{close, dup, dup2, pipe2, O_NONBLOCK, STDERR_FILENO}; + +// Opens a pipe and puts the write end into the stderr FD slot. On success, returns the read end of +// the pipe and the old stderr as a pair of files. +fn redirect_stderr() -> Option<(File, File)> { + let mut fds = [-1, -1]; + unsafe { + // Trivially safe because the return value is checked. + let old_stderr = dup(STDERR_FILENO); + if old_stderr == -1 { + return None; + } + // Safe because pipe2 will only ever write two integers to our array and we check output. + let mut ret = pipe2(fds.as_mut_ptr(), O_NONBLOCK); + if ret != 0 { + // Leaks FDs, but not important right before abort. + return None; + } + // Safe because the FD we are duplicating is owned by us. + ret = dup2(fds[1], STDERR_FILENO); + if ret == -1 { + // Leaks FDs, but not important right before abort. + return None; + } + // The write end is no longer needed. + close(fds[1]); + // Safe because each of the fds was the result of a successful FD creation syscall. + Some((File::from_raw_fd(fds[0]), File::from_raw_fd(old_stderr))) + } +} + +// Sets stderr to the given file. Returns true on success. +fn restore_stderr(stderr: File) -> bool { + let fd = stderr.into_raw_fd(); + + // Safe because fd is guaranteed to be valid and replacing stderr should be an atomic operation. + unsafe { dup2(fd, STDERR_FILENO) != -1 } +} + +// Sends as much information about the panic as possible to syslog. +fn log_panic_info( + default_panic: &Box, + info: &PanicInfo, +) { + // Grab a lock of stderr to prevent concurrent threads from trampling on our stderr capturing + // procedure. The default_panic procedure likely uses stderr.lock as well, but the mutex inside + // stderr is reentrant, so it will not dead-lock on this thread. + let stderr = stderr(); + let _stderr_lock = stderr.lock(); + + // Redirect stderr to a pipe we can read from later. + let (mut read_file, old_stderr) = match redirect_stderr() { + Some(f) => f, + None => { + error!("failed to capture stderr during panic"); + return; + } + }; + // Only through the default panic handler can we get a stacktrace. It only ever prints to + // stderr, hence all the previous code to redirect it to a pipe we can read. + env::set_var("RUST_BACKTRACE", "1"); + default_panic(info); + + // Closes the write end of the pipe so that we can reach EOF in read_to_string. Also allows + // others to write to stderr without failure. + if !restore_stderr(old_stderr) { + error!("failed to restore stderr during panic"); + return; + } + drop(_stderr_lock); + + let mut panic_output = String::new(); + // Ignore errors and print what we got. + let _ = read_file.read_to_string(&mut panic_output); + // Split by line because the logging facilities do not handle embedded new lines well. + for line in panic_output.lines() { + error!("{}", line); + } +} + +/// The intent of our panic hook is to get panic info and a stacktrace into the syslog, even for +/// jailed subprocesses. It will always abort on panic to ensure a minidump is generated. +/// +/// Note that jailed processes will usually have a stacktrace of because the backtrace +/// routines attempt to open this binary and are unable to do so in a jail. +pub fn set_panic_hook() { + let default_panic = panic::take_hook(); + panic::set_hook(Box::new(move |info| { + log_panic_info(&default_panic, info); + // Abort to trigger the crash reporter so that a minidump is generated. + abort(); + })); +}