[release-branch.go1.20] mime/multipart: avoid excessive copy buffer allocations in ReadForm
When copying form data to disk with io.Copy,
allocate only one copy buffer and reuse it rather than
creating two buffers per file (one from io.multiReader.WriteTo,
and a second one from os.File.ReadFrom).
Thanks to Jakob Ackermann (@das7pad) for reporting this issue.
For CVE-2023-24536
For #59153
For #59270
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1802453
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Change-Id: I44ef17c4b4964cdac2858317275594194801fee3
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1802398
Run-TryBot: Roland Shoemaker <bracewell@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/481989
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
diff --git a/src/mime/multipart/formdata.go b/src/mime/multipart/formdata.go
index 41bc886..69b8b03 100644
--- a/src/mime/multipart/formdata.go
+++ b/src/mime/multipart/formdata.go
@@ -85,6 +85,7 @@
maxMemoryBytes = math.MaxInt64
}
}
+ var copyBuf []byte
for {
p, err := r.nextPart(false, maxMemoryBytes)
if err == io.EOF {
@@ -148,14 +149,22 @@
}
}
numDiskFiles++
- size, err := io.Copy(file, io.MultiReader(&b, p))
+ if _, err := file.Write(b.Bytes()); err != nil {
+ return nil, err
+ }
+ if copyBuf == nil {
+ copyBuf = make([]byte, 32*1024) // same buffer size as io.Copy uses
+ }
+ // os.File.ReadFrom will allocate its own copy buffer if we let io.Copy use it.
+ type writerOnly struct{ io.Writer }
+ remainingSize, err := io.CopyBuffer(writerOnly{file}, p, copyBuf)
if err != nil {
return nil, err
}
fh.tmpfile = file.Name()
- fh.Size = size
+ fh.Size = int64(b.Len()) + remainingSize
fh.tmpoff = fileOff
- fileOff += size
+ fileOff += fh.Size
if !combineFiles {
if err := file.Close(); err != nil {
return nil, err
diff --git a/src/mime/multipart/formdata_test.go b/src/mime/multipart/formdata_test.go
index 8a862be..60f55b4 100644
--- a/src/mime/multipart/formdata_test.go
+++ b/src/mime/multipart/formdata_test.go
@@ -368,3 +368,52 @@
t.Fatalf("temp dir contains %v files; want 0", len(names))
}
}
+
+func BenchmarkReadForm(b *testing.B) {
+ for _, test := range []struct {
+ name string
+ form func(fw *Writer, count int)
+ }{{
+ name: "fields",
+ form: func(fw *Writer, count int) {
+ for i := 0; i < count; i++ {
+ w, _ := fw.CreateFormField(fmt.Sprintf("field%v", i))
+ fmt.Fprintf(w, "value %v", i)
+ }
+ },
+ }, {
+ name: "files",
+ form: func(fw *Writer, count int) {
+ for i := 0; i < count; i++ {
+ w, _ := fw.CreateFormFile(fmt.Sprintf("field%v", i), fmt.Sprintf("file%v", i))
+ fmt.Fprintf(w, "value %v", i)
+ }
+ },
+ }} {
+ b.Run(test.name, func(b *testing.B) {
+ for _, maxMemory := range []int64{
+ 0,
+ 1 << 20,
+ } {
+ var buf bytes.Buffer
+ fw := NewWriter(&buf)
+ test.form(fw, 10)
+ if err := fw.Close(); err != nil {
+ b.Fatal(err)
+ }
+ b.Run(fmt.Sprintf("maxMemory=%v", maxMemory), func(b *testing.B) {
+ b.ReportAllocs()
+ for i := 0; i < b.N; i++ {
+ fr := NewReader(bytes.NewReader(buf.Bytes()), fw.Boundary())
+ form, err := fr.ReadForm(maxMemory)
+ if err != nil {
+ b.Fatal(err)
+ }
+ form.RemoveAll()
+ }
+
+ })
+ }
+ })
+ }
+}
