fix: security & privacy (rate limiter fix, csrf session cookie, logout on server, drafts stale token passw, login timing, password over 72b, JWT_SECRET complexity, SMTP TLS, CSV export neutralised, fonts bundled, upload metadata, hourly cleanup job, privacy.md report)

internal/infrastructure/imaging/pngMetadata.go

@@ -0,0 +1,86 @@
+package imaging
+
+import (
+	"bytes"
+	"encoding/binary"
+	"hash/crc32"
+)
+
+const (
+	pngChunkHeaderSize = 8
+	pngChunkCRCSize    = 4
+	pngIHDR            = "IHDR"
+	pngIEND            = "IEND"
+	pngEXIF            = "eXIf"
+)
+
+var pngSignature = []byte("\x89PNG\r\n\x1a\n")
+
+var pngMetadataChunks = map[string]bool{
+	pngEXIF: true,
+	"tEXt":  true,
+	"zTXt":  true,
+	"iTXt":  true,
+	"tIME":  true,
+}
+
+func stripPNG(data []byte) ([]byte, error) {
+	if !bytes.HasPrefix(data, pngSignature) {
+		return nil, errMalformedContainer
+	}
+
+	out := bytes.Clone(pngSignature)
+	orientation := uint16(uprightOrientation)
+	insertAt := 0
+
+	for pos := len(pngSignature); pos < len(data); {
+		available := len(data) - pos - pngChunkHeaderSize - pngChunkCRCSize
+		if available < 0 {
+			return nil, errMalformedContainer
+		}
+		size := binary.BigEndian.Uint32(data[pos:])
+		if uint64(size) > uint64(available) {
+			return nil, errMalformedContainer
+		}
+		kind := string(data[pos+4 : pos+pngChunkHeaderSize])
+		payload := data[pos+pngChunkHeaderSize : pos+pngChunkHeaderSize+int(size)]
+		end := pos + pngChunkHeaderSize + len(payload) + pngChunkCRCSize
+
+		if pngMetadataChunks[kind] {
+			if kind == pngEXIF {
+				if found, ok := exifOrientation(payload); ok {
+					orientation = found
+				}
+			}
+		} else {
+			out = append(out, data[pos:end]...)
+			if kind == pngIHDR {
+				insertAt = len(out)
+			}
+		}
+		pos = end
+
+		if kind == pngIEND {
+			return withPNGOrientation(out, insertAt, orientation)
+		}
+	}
+	return nil, errMalformedContainer
+}
+
+func withPNGOrientation(out []byte, insertAt int, orientation uint16) ([]byte, error) {
+	if !needsOrientation(orientation) {
+		return out, nil
+	}
+	if insertAt == 0 {
+		return nil, errMalformedContainer
+	}
+	chunk := pngChunk(pngEXIF, orientationOnlyTIFF(orientation))
+	return append(out[:insertAt:insertAt], append(chunk, out[insertAt:]...)...), nil
+}
+
+func pngChunk(kind string, payload []byte) []byte {
+	chunk := binary.BigEndian.AppendUint32(nil, uint32(len(payload)))
+	chunk = append(chunk, kind...)
+	chunk = append(chunk, payload...)
+	return binary.BigEndian.AppendUint32(chunk, crc32.ChecksumIEEE(chunk[4:]))
+}