1 files changed, 108 insertions, 0 deletions
diff --git a/pkg/sentry/loader/interpreter.go b/pkg/sentry/loader/interpreter.go
new file mode 100644
index 000000000..3886b4d33
--- /dev/null
+++ b/pkg/sentry/loader/interpreter.go
@@ -0,0 +1,108 @@
+// 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
+}