| 1 | package main |
| 2 | |
| 3 | import ( |
| 4 | "bytes" |
| 5 | "errors" |
| 6 | "fmt" |
| 7 | "image" |
| 8 | _ "image/gif" |
| 9 | _ "image/jpeg" |
| 10 | _ "image/png" |
| 11 | "io" |
| 12 | "os" |
| 13 | |
| 14 | _ "golang.org/x/image/bmp" |
| 15 | "golang.org/x/image/webp" |
| 16 | ) |
| 17 | |
| 18 | const markdownImageMaxPixels int64 = 40_000_000 |
| 19 | |
| 20 | var errMarkdownImageTooLarge = errors.New("markdown image exceeds the decode budget") |
| 21 | |
| 22 | func validateOpenMarkdownImageFile(f *os.File, mimeType string, size int64) error { |
| 23 | if size <= 0 { |
| 24 | return fmt.Errorf("empty image") |
| 25 | } |
| 26 | if size > remoteMarkdownImageMaxBytes { |
| 27 | return errMarkdownImageTooLarge |
| 28 | } |
| 29 | return validateMarkdownImageConfig(f, mimeType) |
| 30 | } |
| 31 | |
| 32 | func validateMarkdownImageBytes(body []byte, mimeType string) error { |
| 33 | if len(body) == 0 { |
| 34 | return fmt.Errorf("empty image") |
| 35 | } |
| 36 | if len(body) > remoteMarkdownImageMaxBytes { |
| 37 | return errMarkdownImageTooLarge |
| 38 | } |
| 39 | return validateMarkdownImageConfig(bytes.NewReader(body), mimeType) |
| 40 | } |
| 41 | |
| 42 | func validateMarkdownImageConfig(r io.Reader, mimeType string) error { |
| 43 | // SVG is sanitized by the remote proxy and does not allocate a source-sized |
| 44 | // raster during Go-side validation. ICO remains byte-bounded; Go has no |
| 45 | // decoder for it in the supported dependency set. |
| 46 | if mimeType == "image/svg+xml" || mimeType == "image/x-icon" { |
| 47 | return nil |
| 48 | } |
| 49 | |
| 50 | var ( |
| 51 | cfg image.Config |
| 52 | format string |
| 53 | err error |
| 54 | ) |
| 55 | if mimeType == "image/webp" { |
| 56 | cfg, err = webp.DecodeConfig(r) |
| 57 | format = "webp" |
| 58 | } else { |
| 59 | cfg, format, err = image.DecodeConfig(r) |
| 60 | } |
| 61 | if err != nil { |
| 62 | return fmt.Errorf("decode image config: %w", err) |
| 63 | } |
| 64 | wantFormat := map[string]string{ |
| 65 | "image/png": "png", |
| 66 | "image/jpeg": "jpeg", |
| 67 | "image/gif": "gif", |
| 68 | "image/bmp": "bmp", |
| 69 | "image/webp": "webp", |
| 70 | }[mimeType] |
| 71 | if wantFormat == "" || format != wantFormat { |
| 72 | return fmt.Errorf("image MIME/format mismatch: %s/%s", mimeType, format) |
| 73 | } |
| 74 | if cfg.Width <= 0 || cfg.Height <= 0 { |
| 75 | return fmt.Errorf("invalid image dimensions") |
| 76 | } |
| 77 | if int64(cfg.Width) > markdownImageMaxPixels/int64(cfg.Height) { |
| 78 | return errMarkdownImageTooLarge |
| 79 | } |
| 80 | return nil |
| 81 | } |
| 82 |