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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package loader
import (
"bytes"
"io"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/sentry/fsbridge"
"gvisor.dev/gvisor/pkg/syserror"
"gvisor.dev/gvisor/pkg/usermem"
)
const (
// interpreterScriptMagic identifies an interpreter script.
interpreterScriptMagic = "#!"
// interpMaxLineLength is the maximum length for the first line of an
// interpreter script.
//
// From execve(2): "A maximum line length of 127 characters is allowed
// for the first line in a #! executable shell script."
interpMaxLineLength = 127
)
// parseInterpreterScript returns the interpreter path and argv.
func parseInterpreterScript(ctx context.Context, filename string, f fsbridge.File, argv []string) (newpath string, newargv []string, err error) {
line := make([]byte, interpMaxLineLength)
n, err := f.ReadFull(ctx, usermem.BytesIOSequence(line), 0)
// Short read is OK.
if err != nil && err != io.ErrUnexpectedEOF {
if err == io.EOF {
err = syserror.ENOEXEC
}
return "", []string{}, err
}
line = line[:n]
if !bytes.Equal(line[:2], []byte(interpreterScriptMagic)) {
return "", []string{}, syserror.ENOEXEC
}
// Ignore #!.
line = line[2:]
// Ignore everything after newline.
// Linux silently truncates the remainder of the line if it exceeds
// interpMaxLineLength.
i := bytes.IndexByte(line, '\n')
if i >= 0 {
line = line[:i]
}
// Skip any whitespace before the interpeter.
line = bytes.TrimLeft(line, " \t")
// Linux only looks for spaces or tabs delimiting the interpreter and
// arg.
//
// execve(2): "On Linux, the entire string following the interpreter
// name is passed as a single argument to the interpreter, and this
// string can include white space."
interp := line
var arg []byte
i = bytes.IndexAny(line, " \t")
if i >= 0 {
interp = line[:i]
arg = bytes.TrimLeft(line[i:], " \t")
}
if string(interp) == "" {
ctx.Infof("Interpreter script contains no interpreter: %v", line)
return "", []string{}, syserror.ENOEXEC
}
// Build the new argument list:
//
// 1. The interpreter.
newargv = append(newargv, string(interp))
// 2. The optional interpreter argument.
if len(arg) > 0 {
newargv = append(newargv, string(arg))
}
// 3. The original arguments. The original argv[0] is replaced with the
// full script filename.
if len(argv) > 0 {
argv[0] = filename
} else {
argv = []string{filename}
}
newargv = append(newargv, argv...)
return string(interp), newargv, nil
}
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