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vmm: fall back if CLONE_CLEAR_SIGHAND unsupported

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This will allow the SIGWINCH listener to run on kernels older than
5.5, although on those kernels it will have to make 64 syscalls to
reset all the signal handlers.

Signed-off-by: Alyssa Ross <hi@alyssa.is>
This commit is contained in:
Alyssa Ross
2023-03-23 17:10:19 +00:00
committed by Rob Bradford
parent 505f4dfa53
commit c1f555cde3
4 changed files with 41 additions and 14 deletions
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47
vmm/src/sigwinch_listener.rs
View File

@@ -2,10 +2,11 @@
// SPDX-License-Identifier: Apache-2.0
use crate::clone3::{clone3, clone_args, CLONE_CLEAR_SIGHAND};
use arch::_NSIG;
use libc::{
c_int, c_void, close, getpgrp, ioctl, pipe2, poll, pollfd, setsid, sigemptyset, siginfo_t,
sigprocmask, syscall, tcsetpgrp, SYS_close_range, ENOSYS, O_CLOEXEC, POLLERR, SIGWINCH,
SIG_SETMASK, STDERR_FILENO, TIOCSCTTY,
c_int, c_void, close, fork, getpgrp, ioctl, pipe2, poll, pollfd, setsid, sigemptyset,
siginfo_t, signal, sigprocmask, syscall, tcsetpgrp, SYS_close_range, EINVAL, ENOSYS, O_CLOEXEC,
POLLERR, SIGWINCH, SIG_DFL, SIG_SETMASK, STDERR_FILENO, TIOCSCTTY,
};
use seccompiler::{apply_filter, BpfProgram};
use std::cell::RefCell;
@@ -176,6 +177,35 @@ fn sigwinch_listener_main(seccomp_filter: BpfProgram, tx: File, pty: File) -> !
exit(0);
}
/// # Safety
///
/// Same as [`fork`].
unsafe fn clone_clear_sighand() -> io::Result<u64> {
let mut args = clone_args::default();
args.flags |= CLONE_CLEAR_SIGHAND;
let r = clone3(&mut args, size_of::<clone_args>());
if r != -1 {
return Ok(r.try_into().unwrap());
}
let e = io::Error::last_os_error();
if e.raw_os_error() != Some(ENOSYS) && e.raw_os_error() != Some(EINVAL) {
return Err(e);
}
// If CLONE_CLEAR_SIGHAND isn't available, fall back to resetting
// all the signal handlers one by one.
let r = fork();
if r == -1 {
return Err(io::Error::last_os_error());
}
if r == 0 {
for signum in 1.._NSIG {
let _ = signal(signum, SIG_DFL);
}
}
Ok(r.try_into().unwrap())
}
pub fn start_sigwinch_listener(seccomp_filter: BpfProgram, tty_sub: File) -> io::Result<File> {
let mut pipe = [-1; 2];
// SAFETY: FFI call with valid arguments
@@ -188,16 +218,9 @@ pub fn start_sigwinch_listener(seccomp_filter: BpfProgram, tty_sub: File) -> io:
// SAFETY: pipe[1] is valid
let tx = unsafe { File::from_raw_fd(pipe[1]) };
let mut args = clone_args::default();
args.flags |= CLONE_CLEAR_SIGHAND;
// SAFETY: FFI call
match unsafe { clone3(&mut args, size_of::<clone_args>()) } {
-1 => return Err(io::Error::last_os_error()),
0 => {
sigwinch_listener_main(seccomp_filter, tx, tty_sub);
}
_ => (),
if unsafe { clone_clear_sighand() }? == 0 {
sigwinch_listener_main(seccomp_filter, tx, tty_sub);
}
drop(tx);