gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/pkg/sentry/loader/interpreter.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  package loader
    16  
    17  import (
    18  	"bytes"
    19  	"io"
    20  
    21  	"gvisor.dev/gvisor/pkg/context"
    22  	"gvisor.dev/gvisor/pkg/errors/linuxerr"
    23  	"gvisor.dev/gvisor/pkg/sentry/vfs"
    24  	"gvisor.dev/gvisor/pkg/usermem"
    25  )
    26  
    27  const (
    28  	// interpreterScriptMagic identifies an interpreter script.
    29  	interpreterScriptMagic = "#!"
    30  
    31  	// interpMaxLineLength is the maximum length for the first line of an
    32  	// interpreter script.
    33  	//
    34  	// From execve(2): "A maximum line length of 127 characters is allowed
    35  	// for the first line in a #! executable shell script."
    36  	interpMaxLineLength = 127
    37  )
    38  
    39  // parseInterpreterScript returns the interpreter path and argv.
    40  func parseInterpreterScript(ctx context.Context, filename string, fd *vfs.FileDescription, argv []string) (newpath string, newargv []string, err error) {
    41  	line := make([]byte, interpMaxLineLength)
    42  	n, err := fd.ReadFull(ctx, usermem.BytesIOSequence(line), 0)
    43  	// Short read is OK.
    44  	if err != nil && err != io.ErrUnexpectedEOF {
    45  		if err == io.EOF {
    46  			err = linuxerr.ENOEXEC
    47  		}
    48  		return "", []string{}, err
    49  	}
    50  	line = line[:n]
    51  
    52  	if !bytes.Equal(line[:2], []byte(interpreterScriptMagic)) {
    53  		return "", []string{}, linuxerr.ENOEXEC
    54  	}
    55  	// Ignore #!.
    56  	line = line[2:]
    57  
    58  	// Ignore everything after newline.
    59  	// Linux silently truncates the remainder of the line if it exceeds
    60  	// interpMaxLineLength.
    61  	i := bytes.IndexByte(line, '\n')
    62  	if i >= 0 {
    63  		line = line[:i]
    64  	}
    65  
    66  	// Skip any whitespace before the interpreter.
    67  	line = bytes.TrimLeft(line, " \t")
    68  
    69  	// Linux only looks for spaces or tabs delimiting the interpreter and
    70  	// arg.
    71  	//
    72  	// execve(2): "On Linux, the entire string following the interpreter
    73  	// name is passed as a single argument to the interpreter, and this
    74  	// string can include white space."
    75  	interp := line
    76  	var arg []byte
    77  	i = bytes.IndexAny(line, " \t")
    78  	if i >= 0 {
    79  		interp = line[:i]
    80  		arg = bytes.TrimLeft(line[i:], " \t")
    81  	}
    82  
    83  	if string(interp) == "" {
    84  		ctx.Infof("Interpreter script contains no interpreter: %v", line)
    85  		return "", []string{}, linuxerr.ENOEXEC
    86  	}
    87  
    88  	// Build the new argument list:
    89  	//
    90  	// 1. The interpreter.
    91  	newargv = append(newargv, string(interp))
    92  
    93  	// 2. The optional interpreter argument.
    94  	if len(arg) > 0 {
    95  		newargv = append(newargv, string(arg))
    96  	}
    97  
    98  	// 3. The original arguments. The original argv[0] is replaced with the
    99  	// full script filename.
   100  	if len(argv) > 0 {
   101  		argv[0] = filename
   102  	} else {
   103  		argv = []string{filename}
   104  	}
   105  	newargv = append(newargv, argv...)
   106  
   107  	return string(interp), newargv, nil
   108  }