fix(pdfengines): require uploaded stamp/watermark file for image or pdf source

pkg/modules/chromium/routes.go

@@ -465,11 +465,13 @@ func convertUrlRoute(chromium Api, engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("reject URL scheme: %w", err)
 			}
 
-			if (watermark.Source == gotenberg.StampSourceImage || watermark.Source == gotenberg.StampSourcePDF) && watermarkFile != "" {
-				watermark.Expression = watermarkFile
+			err = pdfengines.EnsureWatermarkFile(&watermark, watermarkFile)
+			if err != nil {
+				return fmt.Errorf("validate watermark: %w", err)
 			}
-			if (stamp.Source == gotenberg.StampSourceImage || stamp.Source == gotenberg.StampSourcePDF) && stampFile != "" {
-				stamp.Expression = stampFile
+			err = pdfengines.EnsureStampFile(&stamp, stampFile)
+			if err != nil {
+				return fmt.Errorf("validate stamp: %w", err)
 			}
 
 			err = convertUrl(ctx, chromium, engine, url, options, mode, pdfFormats, metadata, userPassword, ownerPassword, embedPaths, embedsMetadata, watermark, stamp, rotateAngle, rotatePages)
@@ -546,11 +548,13 @@ func convertHtmlRoute(chromium Api, engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("validate form data: %w", err)
 			}
 
-			if (watermark.Source == gotenberg.StampSourceImage || watermark.Source == gotenberg.StampSourcePDF) && watermarkFile != "" {
-				watermark.Expression = watermarkFile
+			err = pdfengines.EnsureWatermarkFile(&watermark, watermarkFile)
+			if err != nil {
+				return fmt.Errorf("validate watermark: %w", err)
 			}
-			if (stamp.Source == gotenberg.StampSourceImage || stamp.Source == gotenberg.StampSourcePDF) && stampFile != "" {
-				stamp.Expression = stampFile
+			err = pdfengines.EnsureStampFile(&stamp, stampFile)
+			if err != nil {
+				return fmt.Errorf("validate stamp: %w", err)
 			}
 
 			url := fmt.Sprintf("file://%s", inputPath)
@@ -631,11 +635,13 @@ func convertMarkdownRoute(chromium Api, engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("validate form data: %w", err)
 			}
 
-			if (watermark.Source == gotenberg.StampSourceImage || watermark.Source == gotenberg.StampSourcePDF) && watermarkFile != "" {
-				watermark.Expression = watermarkFile
+			err = pdfengines.EnsureWatermarkFile(&watermark, watermarkFile)
+			if err != nil {
+				return fmt.Errorf("validate watermark: %w", err)
 			}
-			if (stamp.Source == gotenberg.StampSourceImage || stamp.Source == gotenberg.StampSourcePDF) && stampFile != "" {
-				stamp.Expression = stampFile
+			err = pdfengines.EnsureStampFile(&stamp, stampFile)
+			if err != nil {
+				return fmt.Errorf("validate stamp: %w", err)
 			}
 
 			url, err := markdownToHtml(ctx, inputPath, markdownPaths)

pkg/modules/libreoffice/routes.go

@@ -304,11 +304,13 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 				return fmt.Errorf("validate form data: %w", err)
 			}
 
-			if (watermark.Source == gotenberg.StampSourceImage || watermark.Source == gotenberg.StampSourcePDF) && watermarkFile != "" {
-				watermark.Expression = watermarkFile
+			err = pdfengines.EnsureWatermarkFile(&watermark, watermarkFile)
+			if err != nil {
+				return fmt.Errorf("validate watermark: %w", err)
 			}
-			if (stamp.Source == gotenberg.StampSourceImage || stamp.Source == gotenberg.StampSourcePDF) && stampFile != "" {
-				stamp.Expression = stampFile
+			err = pdfengines.EnsureStampFile(&stamp, stampFile)
+			if err != nil {
+				return fmt.Errorf("validate stamp: %w", err)
 			}
 
 			err = pdfengines.ValidatePdfFormatsCompat(pdfFormats, userPassword, embedPaths)

pkg/modules/pdfengines/routes.go

@@ -608,6 +608,50 @@ func FormDataPdfStampFile(form *api.FormData) string {
 	return path
 }
 
+// EnsureStampFile validates that, when stamp.Source is image or pdf, an
+// uploaded stamp file was supplied, and replaces stamp.Expression with
+// uploadedFile in that case. Returning an [api] HTTP 400 error prevents
+// an anonymous caller from passing an arbitrary filesystem path via
+// stampExpression and having pdfcpu read it. Source values of text or
+// empty are passed through unchanged.
+func EnsureStampFile(stamp *gotenberg.Stamp, uploadedFile string) error {
+	if stamp.Source != gotenberg.StampSourceImage && stamp.Source != gotenberg.StampSourcePDF {
+		return nil
+	}
+	if uploadedFile == "" {
+		return api.WrapError(
+			errors.New("no stamp file provided for image or pdf source"),
+			api.NewSentinelHttpError(
+				http.StatusBadRequest,
+				"Invalid form data: a stamp file is required for image or pdf source",
+			),
+		)
+	}
+	stamp.Expression = uploadedFile
+	return nil
+}
+
+// EnsureWatermarkFile mirrors [EnsureStampFile] for a watermark. The
+// shape is identical: image or pdf sources must be accompanied by an
+// uploaded file, and the file path replaces watermark.Expression to
+// prevent pdfcpu from reading an attacker-controlled path.
+func EnsureWatermarkFile(watermark *gotenberg.Stamp, uploadedFile string) error {
+	if watermark.Source != gotenberg.StampSourceImage && watermark.Source != gotenberg.StampSourcePDF {
+		return nil
+	}
+	if uploadedFile == "" {
+		return api.WrapError(
+			errors.New("no watermark file provided for image or pdf source"),
+			api.NewSentinelHttpError(
+				http.StatusBadRequest,
+				"Invalid form data: a watermark file is required for image or pdf source",
+			),
+		)
+	}
+	watermark.Expression = uploadedFile
+	return nil
+}
+
 // WatermarkStub applies a watermark to a list of PDF files. If the stamp has
 // no source, it does nothing.
 func WatermarkStub(ctx *api.Context, engine gotenberg.PdfEngine, stamp gotenberg.Stamp, inputPaths []string) error {
@@ -676,11 +720,13 @@ func mergeRoute(engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("validate form data: %w", err)
 			}
 
-			if (watermark.Source == gotenberg.StampSourceImage || watermark.Source == gotenberg.StampSourcePDF) && watermarkFile != "" {
-				watermark.Expression = watermarkFile
+			err = EnsureWatermarkFile(&watermark, watermarkFile)
+			if err != nil {
+				return fmt.Errorf("validate watermark: %w", err)
 			}
-			if (stamp.Source == gotenberg.StampSourceImage || stamp.Source == gotenberg.StampSourcePDF) && stampFile != "" {
-				stamp.Expression = stampFile
+			err = EnsureStampFile(&stamp, stampFile)
+			if err != nil {
+				return fmt.Errorf("validate stamp: %w", err)
 			}
 
 			err = ValidatePdfFormatsCompat(pdfFormats, userPassword, embedPaths)
@@ -831,11 +877,13 @@ func splitRoute(engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("validate form data: %w", err)
 			}
 
-			if (watermark.Source == gotenberg.StampSourceImage || watermark.Source == gotenberg.StampSourcePDF) && watermarkFile != "" {
-				watermark.Expression = watermarkFile
+			err = EnsureWatermarkFile(&watermark, watermarkFile)
+			if err != nil {
+				return fmt.Errorf("validate watermark: %w", err)
 			}
-			if (stamp.Source == gotenberg.StampSourceImage || stamp.Source == gotenberg.StampSourcePDF) && stampFile != "" {
-				stamp.Expression = stampFile
+			err = EnsureStampFile(&stamp, stampFile)
+			if err != nil {
+				return fmt.Errorf("validate stamp: %w", err)
 			}
 
 			err = ValidatePdfFormatsCompat(pdfFormats, userPassword, embedPaths)
@@ -1268,17 +1316,9 @@ func watermarkRoute(engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("validate form data: %w", err)
 			}
 
-			if stamp.Source == gotenberg.StampSourceImage || stamp.Source == gotenberg.StampSourcePDF {
-				if watermarkFile == "" {
-					return api.WrapError(
-						errors.New("no watermark file provided"),
-						api.NewSentinelHttpError(
-							http.StatusBadRequest,
-							"Invalid form data: a watermark file is required for image or pdf source",
-						),
-					)
-				}
-				stamp.Expression = watermarkFile
+			err = EnsureWatermarkFile(&stamp, watermarkFile)
+			if err != nil {
+				return fmt.Errorf("validate watermark: %w", err)
 			}
 
 			err = WatermarkStub(ctx, engine, stamp, inputPaths)
@@ -1319,17 +1359,9 @@ func stampRoute(engine gotenberg.PdfEngine) api.Route {
 				return fmt.Errorf("validate form data: %w", err)
 			}
 
-			if stamp.Source == gotenberg.StampSourceImage || stamp.Source == gotenberg.StampSourcePDF {
-				if stampFile == "" {
-					return api.WrapError(
-						errors.New("no stamp file provided"),
-						api.NewSentinelHttpError(
-							http.StatusBadRequest,
-							"Invalid form data: a stamp file is required for image or pdf source",
-						),
-					)
-				}
-				stamp.Expression = stampFile
+			err = EnsureStampFile(&stamp, stampFile)
+			if err != nil {
+				return fmt.Errorf("validate stamp: %w", err)
 			}
 
 			err = StampStub(ctx, engine, stamp, inputPaths)

test/integration/features/chromium_convert_html.feature

@@ -1188,6 +1188,30 @@ Feature: /forms/chromium/convert/html
     Then the "foo.pdf" PDF should have 1 page(s)
     Then the "foo.pdf" PDF should have 1 image(s)
 
+  Scenario: POST /forms/chromium/convert/html (stampSource=pdf without uploaded stamp file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/chromium/convert/html" endpoint with the following form data and header(s):
+      | files           | testdata/page-1-html/index.html | file  |
+      | stampSource     | pdf                             | field |
+      | stampExpression | /etc/hostname                   | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a stamp file is required for image or pdf source
+      """
+
+  Scenario: POST /forms/chromium/convert/html (watermarkSource=pdf without uploaded watermark file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/chromium/convert/html" endpoint with the following form data and header(s):
+      | files               | testdata/page-1-html/index.html | file  |
+      | watermarkSource     | pdf                             | field |
+      | watermarkExpression | /etc/hostname                   | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a watermark file is required for image or pdf source
+      """
+
   # See: https://github.com/gotenberg/gotenberg/issues/1500.
   Scenario: POST /forms/chromium/convert/html (Long Filename)
     Given I have a default Gotenberg container

test/integration/features/chromium_convert_markdown.feature

@@ -1153,6 +1153,32 @@ Feature: /forms/chromium/convert/markdown
     Then the response status code should be 200
     Then the response header "Content-Type" should be "application/pdf"
 
+  Scenario: POST /forms/chromium/convert/markdown (stampSource=pdf without uploaded stamp file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/chromium/convert/markdown" endpoint with the following form data and header(s):
+      | files           | testdata/page-1-markdown/index.html | file  |
+      | files           | testdata/page-1-markdown/page_1.md  | file  |
+      | stampSource     | pdf                                 | field |
+      | stampExpression | /etc/hostname                       | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a stamp file is required for image or pdf source
+      """
+
+  Scenario: POST /forms/chromium/convert/markdown (watermarkSource=pdf without uploaded watermark file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/chromium/convert/markdown" endpoint with the following form data and header(s):
+      | files               | testdata/page-1-markdown/index.html | file  |
+      | files               | testdata/page-1-markdown/page_1.md  | file  |
+      | watermarkSource     | pdf                                 | field |
+      | watermarkExpression | /etc/hostname                       | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a watermark file is required for image or pdf source
+      """
+
   # See: https://github.com/gotenberg/gotenberg/issues/1500.
   Scenario: POST /forms/chromium/convert/markdown (Long Filename)
     Given I have a default Gotenberg container

test/integration/features/chromium_convert_url.feature

@@ -1269,6 +1269,32 @@ Feature: /forms/chromium/convert/url
     Then the response status code should be 200
     Then the response header "Content-Type" should be "application/pdf"
 
+  Scenario: POST /forms/chromium/convert/url (stampSource=pdf without uploaded stamp file => 400)
+    Given I have a default Gotenberg container
+    Given I have a static server
+    When I make a "POST" request to Gotenberg at the "/forms/chromium/convert/url" endpoint with the following form data and header(s):
+      | url             | http://host.docker.internal:%d/html/testdata/page-1-html/index.html | field |
+      | stampSource     | pdf                                                                 | field |
+      | stampExpression | /etc/hostname                                                       | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a stamp file is required for image or pdf source
+      """
+
+  Scenario: POST /forms/chromium/convert/url (watermarkSource=pdf without uploaded watermark file => 400)
+    Given I have a default Gotenberg container
+    Given I have a static server
+    When I make a "POST" request to Gotenberg at the "/forms/chromium/convert/url" endpoint with the following form data and header(s):
+      | url                 | http://host.docker.internal:%d/html/testdata/page-1-html/index.html | field |
+      | watermarkSource     | pdf                                                                 | field |
+      | watermarkExpression | /etc/hostname                                                       | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a watermark file is required for image or pdf source
+      """
+
   # See: https://github.com/gotenberg/gotenberg/issues/1500.
   Scenario: POST /forms/chromium/convert/url (Long Filename)
     Given I have a default Gotenberg container

test/integration/features/libreoffice_convert.feature

@@ -817,6 +817,30 @@ Feature: /forms/libreoffice/convert
     Then the response status code should be 200
     Then the response header "Content-Type" should be "application/pdf"
 
+  Scenario: POST /forms/libreoffice/convert (stampSource=pdf without uploaded stamp file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/libreoffice/convert" endpoint with the following form data and header(s):
+      | files           | testdata/page_1.docx | file  |
+      | stampSource     | pdf                  | field |
+      | stampExpression | /etc/hostname        | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a stamp file is required for image or pdf source
+      """
+
+  Scenario: POST /forms/libreoffice/convert (watermarkSource=pdf without uploaded watermark file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/libreoffice/convert" endpoint with the following form data and header(s):
+      | files               | testdata/page_1.docx | file  |
+      | watermarkSource     | pdf                  | field |
+      | watermarkExpression | /etc/hostname        | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a watermark file is required for image or pdf source
+      """
+
   # See: https://github.com/gotenberg/gotenberg/issues/1500.
   Scenario: POST /forms/libreoffice/convert (Long Filename)
     Given I have a default Gotenberg container

test/integration/features/pdfengines_merge.feature

@@ -665,6 +665,32 @@ Feature: /forms/pdfengines/merge
       | embeds | testdata/embed_1.xml | file  |
     Then the response status code should be 200
 
+  Scenario: POST /forms/pdfengines/merge (stampSource=pdf without uploaded stamp file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/pdfengines/merge" endpoint with the following form data and header(s):
+      | files           | testdata/page_1.pdf | file  |
+      | files           | testdata/page_2.pdf | file  |
+      | stampSource     | pdf                 | field |
+      | stampExpression | /etc/hostname       | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a stamp file is required for image or pdf source
+      """
+
+  Scenario: POST /forms/pdfengines/merge (watermarkSource=pdf without uploaded watermark file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/pdfengines/merge" endpoint with the following form data and header(s):
+      | files               | testdata/page_1.pdf | file  |
+      | files               | testdata/page_2.pdf | file  |
+      | watermarkSource     | pdf                 | field |
+      | watermarkExpression | /etc/hostname       | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a watermark file is required for image or pdf source
+      """
+
   # See: https://github.com/gotenberg/gotenberg/issues/1500.
   Scenario: POST /forms/pdfengines/merge (Long Filename)
     Given I have a default Gotenberg container

test/integration/features/pdfengines_split.feature

@@ -767,6 +767,34 @@ Feature: /forms/pdfengines/split
       | embeds    | testdata/embed_1.xml | file  |
     Then the response status code should be 200
 
+  Scenario: POST /forms/pdfengines/split (stampSource=pdf without uploaded stamp file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/pdfengines/split" endpoint with the following form data and header(s):
+      | files           | testdata/pages_3.pdf | file  |
+      | splitMode       | intervals            | field |
+      | splitSpan       | 2                    | field |
+      | stampSource     | pdf                  | field |
+      | stampExpression | /etc/hostname        | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a stamp file is required for image or pdf source
+      """
+
+  Scenario: POST /forms/pdfengines/split (watermarkSource=pdf without uploaded watermark file => 400)
+    Given I have a default Gotenberg container
+    When I make a "POST" request to Gotenberg at the "/forms/pdfengines/split" endpoint with the following form data and header(s):
+      | files               | testdata/pages_3.pdf | file  |
+      | splitMode           | intervals            | field |
+      | splitSpan           | 2                    | field |
+      | watermarkSource     | pdf                  | field |
+      | watermarkExpression | /etc/hostname        | field |
+    Then the response status code should be 400
+    Then the response body should match string:
+      """
+      Invalid form data: a watermark file is required for image or pdf source
+      """
+
   # See: https://github.com/gotenberg/gotenberg/issues/1500.
   Scenario: POST /forms/pdfengines/split (Long Filename)
     Given I have a default Gotenberg container