github.com/nicocha30/gvisor-ligolo@v0.0.0-20230726075806-989fa2c0a413/pkg/sighandling/sighandling_linux_unsafe.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  //go:build linux
    16  // +build linux
    17  
    18  package sighandling
    19  
    20  import (
    21  	"fmt"
    22  	"unsafe"
    23  
    24  	"golang.org/x/sys/unix"
    25  	"github.com/nicocha30/gvisor-ligolo/pkg/abi/linux"
    26  )
    27  
    28  // IgnoreChildStop sets the SA_NOCLDSTOP flag, causing child processes to not
    29  // generate SIGCHLD when they stop.
    30  func IgnoreChildStop() error {
    31  	var sa linux.SigAction
    32  
    33  	// Get the existing signal handler information, and set the flag.
    34  	if _, _, e := unix.RawSyscall6(unix.SYS_RT_SIGACTION, uintptr(unix.SIGCHLD), 0, uintptr(unsafe.Pointer(&sa)), linux.SignalSetSize, 0, 0); e != 0 {
    35  		return e
    36  	}
    37  	sa.Flags |= linux.SA_NOCLDSTOP
    38  	if _, _, e := unix.RawSyscall6(unix.SYS_RT_SIGACTION, uintptr(unix.SIGCHLD), uintptr(unsafe.Pointer(&sa)), 0, linux.SignalSetSize, 0, 0); e != 0 {
    39  		return e
    40  	}
    41  
    42  	return nil
    43  }
    44  
    45  // ReplaceSignalHandler replaces the existing signal handler for the provided
    46  // signal with the function pointer at `handler`. This bypasses the Go runtime
    47  // signal handlers, and should only be used for low-level signal handlers where
    48  // use of signal.Notify is not appropriate.
    49  //
    50  // It stores the value of the previously set handler in previous.
    51  func ReplaceSignalHandler(sig unix.Signal, handler uintptr, previous *uintptr) error {
    52  	var sa linux.SigAction
    53  	const maskLen = 8
    54  
    55  	// Get the existing signal handler information, and save the current
    56  	// handler. Once we replace it, we will use this pointer to fall back to
    57  	// it when we receive other signals.
    58  	if _, _, e := unix.RawSyscall6(unix.SYS_RT_SIGACTION, uintptr(sig), 0, uintptr(unsafe.Pointer(&sa)), maskLen, 0, 0); e != 0 {
    59  		return e
    60  	}
    61  
    62  	// Fail if there isn't a previous handler.
    63  	if sa.Handler == 0 {
    64  		return fmt.Errorf("previous handler for signal %x isn't set", sig)
    65  	}
    66  
    67  	*previous = uintptr(sa.Handler)
    68  
    69  	// Install our own handler.
    70  	sa.Handler = uint64(handler)
    71  	if _, _, e := unix.RawSyscall6(unix.SYS_RT_SIGACTION, uintptr(sig), uintptr(unsafe.Pointer(&sa)), 0, maskLen, 0, 0); e != 0 {
    72  		return e
    73  	}
    74  
    75  	return nil
    76  }