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net/http/cgi,net/http/fcgi: add Content-Type detection

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This CL ensures that responses served via CGI and FastCGI
have a Content-Type header based on the content of the
response if not explicitly set by handlers.

If the implementers of the handler did not explicitly
specify a Content-Type both CGI implementations would default
to "text/html", potentially causing cross-site scripting.

Thanks to RedTeam Pentesting GmbH for reporting this.

Fixes #40928
Fixes CVE-2020-24553

Change-Id: I82cfc396309b5ab2e8d6e9a87eda8ea7e3799473
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/823217
Reviewed-by: Russ Cox <rsc@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/252179
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
This commit is contained in:
Roberto Clapis 2020-08-26 08:53:03 +02:00 committed by Filippo Valsorda
parent 66e66e7113
commit 4f5cd0c033
5 changed files with 217 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
src/net/http/cgi/child.go
View File

@ -168,8 +168,10 @@ func Serve(handler http.Handler) error {
type response struct {
req *http.Request
header http.Header
code int
wroteHeader bool
wroteCGIHeader bool
bufw *bufio.Writer
headerSent bool
}
func (r *response) Flush() {
@ -181,26 +183,38 @@ func (r *response) Header() http.Header {
}
func (r *response) Write(p []byte) (n int, err error) {
if !r.headerSent {
if !r.wroteHeader {
r.WriteHeader(http.StatusOK)
}
if !r.wroteCGIHeader {
r.writeCGIHeader(p)
}
return r.bufw.Write(p)
}
func (r *response) WriteHeader(code int) {
if r.headerSent {
if r.wroteHeader {
// Note: explicitly using Stderr, as Stdout is our HTTP output.
fmt.Fprintf(os.Stderr, "CGI attempted to write header twice on request for %s", r.req.URL)
return
}
r.headerSent = true
fmt.Fprintf(r.bufw, "Status: %d %s\r\n", code, http.StatusText(code))
// Set a default Content-Type
if _, hasType := r.header["Content-Type"]; !hasType {
r.header.Add("Content-Type", "text/html; charset=utf-8")
r.wroteHeader = true
r.code = code
}
// writeCGIHeader finalizes the header sent to the client and writes it to the output.
// p is not written by writeHeader, but is the first chunk of the body
// that will be written. It is sniffed for a Content-Type if none is
// set explicitly.
func (r *response) writeCGIHeader(p []byte) {
if r.wroteCGIHeader {
return
}
r.wroteCGIHeader = true
fmt.Fprintf(r.bufw, "Status: %d %s\r\n", r.code, http.StatusText(r.code))
if _, hasType := r.header["Content-Type"]; !hasType {
r.header.Set("Content-Type", http.DetectContentType(p))
}
r.header.Write(r.bufw)
r.bufw.WriteString("\r\n")
r.bufw.Flush()

58
src/net/http/cgi/child_test.go
View File

@ -7,6 +7,11 @@
package cgi
import (
"bufio"
"bytes"
"net/http"
"net/http/httptest"
"strings"
"testing"
)
@ -148,3 +153,56 @@ func TestRequestWithoutRemotePort(t *testing.T) {
t.Errorf("RemoteAddr: got %q; want %q", g, e)
}
}
func TestResponse(t *testing.T) {
var tests = []struct {
name string
body string
wantCT string
}{
{
name: "no body",
wantCT: "text/plain; charset=utf-8",
},
{
name: "html",
body: "<html><head><title>test page</title></head><body>This is a body</body></html>",
wantCT: "text/html; charset=utf-8",
},
{
name: "text",
body: strings.Repeat("gopher", 86),
wantCT: "text/plain; charset=utf-8",
},
{
name: "jpg",
body: "\xFF\xD8\xFF" + strings.Repeat("B", 1024),
wantCT: "image/jpeg",
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
var buf bytes.Buffer
resp := response{
req: httptest.NewRequest("GET", "/", nil),
header: http.Header{},
bufw: bufio.NewWriter(&buf),
}
n, err := resp.Write([]byte(tt.body))
if err != nil {
t.Errorf("Write: unexpected %v", err)
}
if want := len(tt.body); n != want {
t.Errorf("reported short Write: got %v want %v", n, want)
}
resp.writeCGIHeader(nil)
resp.Flush()
if got := resp.Header().Get("Content-Type"); got != tt.wantCT {
t.Errorf("wrong content-type: got %q, want %q", got, tt.wantCT)
}
if !bytes.HasSuffix(buf.Bytes(), []byte(tt.body)) {
t.Errorf("body was not correctly written")
}
})
}
}

53
src/net/http/cgi/integration_test.go
View File

@ -16,7 +16,9 @@ import (
"io"
"net/http"
"net/http/httptest"
"net/url"
"os"
"strings"
"testing"
"time"
)
@ -52,7 +54,7 @@ func TestHostingOurselves(t *testing.T) {
}
replay := runCgiTest(t, h, "GET /test.go?foo=bar&a=b HTTP/1.0\nHost: example.com\n\n", expectedMap)
if expected, got := "text/html; charset=utf-8", replay.Header().Get("Content-Type"); got != expected {
if expected, got := "text/plain; charset=utf-8", replay.Header().Get("Content-Type"); got != expected {
t.Errorf("got a Content-Type of %q; expected %q", got, expected)
}
if expected, got := "X-Test-Value", replay.Header().Get("X-Test-Header"); got != expected {
@ -169,6 +171,51 @@ func TestNilRequestBody(t *testing.T) {
_ = runCgiTest(t, h, "POST /test.go?nil-request-body=1 HTTP/1.0\nHost: example.com\nContent-Length: 0\n\n", expectedMap)
}
func TestChildContentType(t *testing.T) {
testenv.MustHaveExec(t)
h := &Handler{
Path: os.Args[0],
Root: "/test.go",
Args: []string{"-test.run=TestBeChildCGIProcess"},
}
var tests = []struct {
name string
body string
wantCT string
}{
{
name: "no body",
wantCT: "text/plain; charset=utf-8",
},
{
name: "html",
body: "<html><head><title>test page</title></head><body>This is a body</body></html>",
wantCT: "text/html; charset=utf-8",
},
{
name: "text",
body: strings.Repeat("gopher", 86),
wantCT: "text/plain; charset=utf-8",
},
{
name: "jpg",
body: "\xFF\xD8\xFF" + strings.Repeat("B", 1024),
wantCT: "image/jpeg",
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
expectedMap := map[string]string{"_body": tt.body}
req := fmt.Sprintf("GET /test.go?exact-body=%s HTTP/1.0\nHost: example.com\n\n", url.QueryEscape(tt.body))
replay := runCgiTest(t, h, req, expectedMap)
if got := replay.Header().Get("Content-Type"); got != tt.wantCT {
t.Errorf("got a Content-Type of %q; expected it to start with %q", got, tt.wantCT)
}
})
}
}
// golang.org/issue/7198
func Test500WithNoHeaders(t *testing.T) { want500Test(t, "/immediate-disconnect") }
func Test500WithNoContentType(t *testing.T) { want500Test(t, "/no-content-type") }
@ -224,6 +271,10 @@ func TestBeChildCGIProcess(t *testing.T) {
if req.FormValue("no-body") == "1" {
return
}
if eb, ok := req.Form["exact-body"]; ok {
io.WriteString(rw, eb[0])
return
}
if req.FormValue("write-forever") == "1" {
io.Copy(rw, neverEnding('a'))
for {

33
src/net/http/fcgi/child.go
View File

@ -76,8 +76,10 @@ func (r *request) parseParams() {
type response struct {
req *request
header http.Header
w *bufWriter
code int
wroteHeader bool
wroteCGIHeader bool
w *bufWriter
}
func newResponse(c *child, req *request) *response {
@ -92,11 +94,14 @@ func (r *response) Header() http.Header {
return r.header
}
func (r *response) Write(data []byte) (int, error) {
func (r *response) Write(p []byte) (n int, err error) {
if !r.wroteHeader {
r.WriteHeader(http.StatusOK)
}
return r.w.Write(data)
if !r.wroteCGIHeader {
r.writeCGIHeader(p)
}
return r.w.Write(p)
}
func (r *response) WriteHeader(code int) {
@ -104,22 +109,34 @@ func (r *response) WriteHeader(code int) {
return
}
r.wroteHeader = true
r.code = code
if code == http.StatusNotModified {
// Must not have body.
r.header.Del("Content-Type")
r.header.Del("Content-Length")
r.header.Del("Transfer-Encoding")
} else if r.header.Get("Content-Type") == "" {
r.header.Set("Content-Type", "text/html; charset=utf-8")
}
if r.header.Get("Date") == "" {
r.header.Set("Date", time.Now().UTC().Format(http.TimeFormat))
}
}
fmt.Fprintf(r.w, "Status: %d %s\r\n", code, http.StatusText(code))
// writeCGIHeader finalizes the header sent to the client and writes it to the output.
// p is not written by writeHeader, but is the first chunk of the body
// that will be written. It is sniffed for a Content-Type if none is
// set explicitly.
func (r *response) writeCGIHeader(p []byte) {
if r.wroteCGIHeader {
return
}
r.wroteCGIHeader = true
fmt.Fprintf(r.w, "Status: %d %s\r\n", r.code, http.StatusText(r.code))
if _, hasType := r.header["Content-Type"]; r.code != http.StatusNotModified && !hasType {
r.header.Set("Content-Type", http.DetectContentType(p))
}
r.header.Write(r.w)
r.w.WriteString("\r\n")
r.w.Flush()
}
func (r *response) Flush() {
@ -293,6 +310,8 @@ func (c *child) serveRequest(req *request, body io.ReadCloser) {
httpReq = httpReq.WithContext(envVarCtx)
c.handler.ServeHTTP(r, httpReq)
}
// Make sure we serve something even if nothing was written to r
r.Write(nil)
r.Close()
c.mu.Lock()
delete(c.requests, req.reqId)

52
src/net/http/fcgi/fcgi_test.go
View File

@ -10,6 +10,7 @@ import (
"io"
"io/ioutil"
"net/http"
"strings"
"testing"
)
@ -344,3 +345,54 @@ func TestChildServeReadsEnvVars(t *testing.T) {
<-done
}
}
func TestResponseWriterSniffsContentType(t *testing.T) {
var tests = []struct {
name string
body string
wantCT string
}{
{
name: "no body",
wantCT: "text/plain; charset=utf-8",
},
{
name: "html",
body: "<html><head><title>test page</title></head><body>This is a body</body></html>",
wantCT: "text/html; charset=utf-8",
},
{
name: "text",
body: strings.Repeat("gopher", 86),
wantCT: "text/plain; charset=utf-8",
},
{
name: "jpg",
body: "\xFF\xD8\xFF" + strings.Repeat("B", 1024),
wantCT: "image/jpeg",
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
input := make([]byte, len(streamFullRequestStdin))
copy(input, streamFullRequestStdin)
rc := nopWriteCloser{bytes.NewBuffer(input)}
done := make(chan bool)
var resp *response
c := newChild(rc, http.HandlerFunc(func(
w http.ResponseWriter,
r *http.Request,
) {
io.WriteString(w, tt.body)
resp = w.(*response)
done <- true
}))
defer c.cleanUp()
go c.serve()
<-done
if got := resp.Header().Get("Content-Type"); got != tt.wantCT {
t.Errorf("got a Content-Type of %q; expected it to start with %q", got, tt.wantCT)
}
})
}
}