net/textproto: do not allow multi-line header field names

Fixes #34702

Change-Id: I98320d54726e646a310e583283ddab676c3503e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/199838
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 31 insertions, 4 deletions

diff --git a/src/net/textproto/reader.go b/src/net/textproto/reader.go
index 87f901b4fc..a505da985c 100644
--- a/src/net/textproto/reader.go
+++ b/src/net/textproto/reader.go
@@ -7,6 +7,7 @@ package textproto
 import (
 	"bufio"
 	"bytes"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"strconv"
@@ -90,7 +91,7 @@ func (r *Reader) readLineSlice() ([]byte, error) {
 // A line consisting of only white space is never continued.
 //
 func (r *Reader) ReadContinuedLine() (string, error) {
-	line, err := r.readContinuedLineSlice()
+	line, err := r.readContinuedLineSlice(noValidation)
 	return string(line), err
 }
 
@@ -111,7 +112,7 @@ func trim(s []byte) []byte {
 // ReadContinuedLineBytes is like ReadContinuedLine but
 // returns a []byte instead of a string.
 func (r *Reader) ReadContinuedLineBytes() ([]byte, error) {
-	line, err := r.readContinuedLineSlice()
+	line, err := r.readContinuedLineSlice(noValidation)
 	if line != nil {
 		buf := make([]byte, len(line))
 		copy(buf, line)
@@ -120,7 +121,15 @@ func (r *Reader) ReadContinuedLineBytes() ([]byte, error) {
 	return line, err
 }
 
-func (r *Reader) readContinuedLineSlice() ([]byte, error) {
+// readContinuedLineSlice reads continued lines from the reader buffer,
+// returning a byte slice with all lines. The validateFirstLine function
+// is run on the first read line, and if it returns an error then this
+// error is returned from readContinuedLineSlice.
+func (r *Reader) readContinuedLineSlice(validateFirstLine func([]byte) error) ([]byte, error) {
+	if validateFirstLine == nil {
+		return nil, fmt.Errorf("missing validateFirstLine func")
+	}
+
 	// Read the first line.
 	line, err := r.readLineSlice()
 	if err != nil {
@@ -130,6 +139,10 @@ func (r *Reader) readContinuedLineSlice() ([]byte, error) {
 		return line, nil
 	}
 
+	if err := validateFirstLine(line); err != nil {
+		return nil, err
+	}
+
 	// Optimistically assume that we have started to buffer the next line
 	// and it starts with an ASCII letter (the next header key), or a blank
 	// line, so we can avoid copying that buffered data around in memory
@@ -490,7 +503,7 @@ func (r *Reader) ReadMIMEHeader() (MIMEHeader, error) {
 	}
 
 	for {
-		kv, err := r.readContinuedLineSlice()
+		kv, err := r.readContinuedLineSlice(mustHaveFieldNameColon)
 		if len(kv) == 0 {
 			return m, err
 		}
@@ -535,6 +548,20 @@ func (r *Reader) ReadMIMEHeader() (MIMEHeader, error) {
 	}
 }
 
+// noValidation is a no-op validation func for readContinuedLineSlice
+// that permits any lines.
+func noValidation(_ []byte) error { return nil }
+
+// mustHaveFieldNameColon ensures that, per RFC 7230, the
+// field-name is on a single line, so the first line must
+// contain a colon.
+func mustHaveFieldNameColon(line []byte) error {
+	if bytes.IndexByte(line, ':') < 0 {
+		return ProtocolError(fmt.Sprintf("malformed MIME header: missing colon: %q" + string(line)))
+	}
+	return nil
+}
+
 // upcomingHeaderNewlines returns an approximation of the number of newlines
 // that will be in this header. If it gets confused, it returns 0.
 func (r *Reader) upcomingHeaderNewlines() (n int) {