net/http: ParseMultipartForm panic when the body==nil

[forTWOS]

What version of Go are you using (go version)?

go version go1.17 windows/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

set GO111MODULE=auto
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\xx\AppData\Local\go-build
set GOENV=C:\Users\xx\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\xx\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\xx\go
set GOPRIVATE=
set GOPROXY=https://goproxy.io,direct
set GOROOT=c:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.17
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\xx\AppData\Local\Temp\go-build2679503516=/tmp/go-build -gno-record-gcc-switches

What did you do?

package main

import (
	"bytes"
	"fmt"
	"mime/multipart"
	"net/http"
)

func main() {
	buf := new(bytes.Buffer)
	mw := multipart.NewWriter(buf)
	mw.Close()

	Request, _ := http.NewRequest("POST", "/", nil)
	Request.Header.Set("Content-Type", mw.FormDataContentType())

	f, fh, err := Request.FormFile("file")
	if err != nil {
		fmt.Printf("%#+v\n", err)
		return
	}
	f.Close()
	fmt.Printf("%#+v\n", fh)
	return
}

What did you expect to see?

I would like to see an error.

errors.New("missing form body")

What did you see instead?

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x18 pc=0x77b632]

goroutine 1 [running]:
mime/multipart.(*stickyErrorReader).Read(0xc00005a500, {0xc0000da000, 0x927640, 0x0})
c:/go/src/mime/multipart/multipart.go:127 +0x32
bufio.(*Reader).fill(0xc000066180)
c:/go/src/bufio/bufio.go:101 +0x103
bufio.(*Reader).ReadSlice(0xc000066180, 0x98)
c:/go/src/bufio/bufio.go:360 +0x2f
mime/multipart.(*Reader).nextPart(0xc000022080, 0xf8)
c:/go/src/mime/multipart/multipart.go:335 +0xb6
mime/multipart.(*Reader).NextPart(...)
c:/go/src/mime/multipart/multipart.go:314
mime/multipart.(*Reader).readForm(0xc0000d4000, 0x2000000)
c:/go/src/mime/multipart/formdata.go:52 +0x178
mime/multipart.(*Reader).ReadForm(...)
c:/go/src/mime/multipart/formdata.go:31
net/http.(*Request).ParseMultipartForm(0xc0000d4000, 0x6ad007)
c:/go/src/net/http/request.go:1318 +0xa5
net/http.(*Request).FormFile(0xc0000d4000, {0x7e207c, 0x4})
c:/go/src/net/http/request.go:1376 +0x4f
main.main()
D:/gocode/src/ucenter/app/test/httpformfile/main.go:18 +0x1bb
exit status 2

[seankhliao]

cc @neild

[helbing]

Hi, I've found out why panic. In http.ParseMultipartForm, the method ParseForm returns the error missing form body when Body is equal to nil, and not handled. but Body was used in subsequent function calls (r.multipartReader(false) and mr.ReadForm(maxMemory)).

[gopherbot]

Change https://go.dev/cl/384454 mentions this issue: net/http: fix nil body causing ParseMultipartForm to panic