lp_linux_test.go

     1  // Copyright 2022 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package exec_test
     6  
     7  import (
     8  	"errors"
     9  	"internal/syscall/unix"
    10  	"internal/testenv"
    11  	"os"
    12  	"os/exec"
    13  	"path/filepath"
    14  	"syscall"
    15  	"testing"
    16  )
    17  
    18  func TestFindExecutableVsNoexec(t *testing.T) {
    19  	t.Parallel()
    20  
    21  	// This test case relies on faccessat2(2) syscall, which appeared in Linux v5.8.
    22  	if major, minor := unix.KernelVersion(); major < 5 || (major == 5 && minor < 8) {
    23  		t.Skip("requires Linux kernel v5.8 with faccessat2(2) syscall")
    24  	}
    25  
    26  	tmp := t.TempDir()
    27  
    28  	// Create a tmpfs mount.
    29  	err := syscall.Mount("tmpfs", tmp, "tmpfs", 0, "")
    30  	if testenv.SyscallIsNotSupported(err) {
    31  		// Usually this means lack of CAP_SYS_ADMIN, but there might be
    32  		// other reasons, especially in restricted test environments.
    33  		t.Skipf("requires ability to mount tmpfs (%v)", err)
    34  	} else if err != nil {
    35  		t.Fatalf("mount %s failed: %v", tmp, err)
    36  	}
    37  	t.Cleanup(func() {
    38  		if err := syscall.Unmount(tmp, 0); err != nil {
    39  			t.Error(err)
    40  		}
    41  	})
    42  
    43  	// Create an executable.
    44  	path := filepath.Join(tmp, "program")
    45  	err = os.WriteFile(path, []byte("#!/bin/sh\necho 123\n"), 0o755)
    46  	if err != nil {
    47  		t.Fatal(err)
    48  	}
    49  
    50  	// Check that it works as expected.
    51  	_, err = exec.LookPath(path)
    52  	if err != nil {
    53  		t.Fatalf("LookPath: got %v, want nil", err)
    54  	}
    55  
    56  	for {
    57  		err = exec.Command(path).Run()
    58  		if err == nil {
    59  			break
    60  		}
    61  		if errors.Is(err, syscall.ETXTBSY) {
    62  			// A fork+exec in another process may be holding open the FD that we used
    63  			// to write the executable (see https://go.dev/issue/22315).
    64  			// Since the descriptor should have CLOEXEC set, the problem should resolve
    65  			// as soon as the forked child reaches its exec call.
    66  			// Keep retrying until that happens.
    67  		} else {
    68  			t.Fatalf("exec: got %v, want nil", err)
    69  		}
    70  	}
    71  
    72  	// Remount with noexec flag.
    73  	err = syscall.Mount("", tmp, "", syscall.MS_REMOUNT|syscall.MS_NOEXEC, "")
    74  	if testenv.SyscallIsNotSupported(err) {
    75  		t.Skipf("requires ability to re-mount tmpfs (%v)", err)
    76  	} else if err != nil {
    77  		t.Fatalf("remount %s with noexec failed: %v", tmp, err)
    78  	}
    79  
    80  	if err := exec.Command(path).Run(); err == nil {
    81  		t.Fatal("exec on noexec filesystem: got nil, want error")
    82  	}
    83  
    84  	_, err = exec.LookPath(path)
    85  	if err == nil {
    86  		t.Fatalf("LookPath: got nil, want error")
    87  	}
    88  }
    89
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