fix(packages): limit Maven checksum uploads (#39028) (#39031)

Backport #39028 by @bircni

Bound checksum uploads to the maximum usable digest length before
buffering their content.

Co-authored-by: bircni <bircni@icloud.com>

routers/api/packages/maven/maven.go

@@ -30,6 +30,8 @@ import (
 	packages_service "gitea.dev/services/packages"
 )
 
+const maxChecksumSize = sha512.Size*2 + 1
+
 const (
 	mavenMetadataFile = "maven-metadata.xml"
 	extensionMD5      = ".md5"
@@ -260,12 +262,21 @@ func UploadPackageFile(ctx *context.Context) {
 	}
 	defer releaser()
 
-	buf, err := packages_module.CreateHashedBufferFromReader(ctx.Req.Body)
+	ext := path.Ext(params.Filename)
+	reader := io.Reader(ctx.Req.Body)
+	if isChecksumExtension(ext) {
+		reader = io.LimitReader(reader, maxChecksumSize+1)
+	}
+	buf, err := packages_module.CreateHashedBufferFromReader(reader)
 	if err != nil {
 		apiError(ctx, http.StatusInternalServerError, err)
 		return
 	}
 	defer buf.Close()
+	if isChecksumExtension(ext) && !isChecksumSizeAllowed(buf.Size()) {
+		apiError(ctx, http.StatusRequestEntityTooLarge, "checksum is too large")
+		return
+	}
 
 	pvci := &packages_service.PackageCreationInfo{
 		PackageInfo: packages_service.PackageInfo{
@@ -291,8 +302,6 @@ func UploadPackageFile(ctx *context.Context) {
 		}
 	}
 
-	ext := path.Ext(params.Filename)
-
 	// Do not upload checksum files but compare the hashes.
 	if isChecksumExtension(ext) {
 		pv, err := packages_model.GetVersionByNameAndVersion(ctx, pvci.Owner.ID, pvci.PackageType, pvci.Name, pvci.Version)
@@ -404,6 +413,10 @@ func UploadPackageFile(ctx *context.Context) {
 	ctx.Status(http.StatusCreated)
 }
 
+func isChecksumSizeAllowed(size int64) bool {
+	return size <= maxChecksumSize
+}
+
 func isChecksumExtension(ext string) bool {
 	return ext == extensionMD5 || ext == extensionSHA1 || ext == extensionSHA256 || ext == extensionSHA512
 }

routers/api/packages/maven/maven_test.go

@@ -0,0 +1,15 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package maven
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestChecksumSizeAllowed(t *testing.T) {
+	assert.True(t, isChecksumSizeAllowed(maxChecksumSize))
+	assert.False(t, isChecksumSizeAllowed(maxChecksumSize+1))
+}