[O] Protect against path traversal

src/main/java/ext/Ext.kt

@@ -19,6 +19,7 @@ import org.springframework.http.HttpHeaders
 import org.springframework.http.HttpStatus
 import org.springframework.http.ResponseEntity.BodyBuilder
 import org.springframework.web.bind.annotation.*
+import java.io.File
 import java.lang.reflect.Field
 import java.nio.charset.StandardCharsets
 import java.nio.file.Path
@@ -235,6 +236,7 @@ fun <T> Lock.maybeLock(block: () -> T) = if (tryLock()) try { block() } finally
 fun path(part1: Str, vararg parts: Str) = Path.of(part1, *parts)
 fun Str.path() = Path.of(this)
 operator fun Path.div(part: Str) = resolve(part)
+operator fun File.div(fileName: Str) = File(this, fileName)
 fun Str.ensureEndingSlash() = if (endsWith('/')) this else "$this/"
 
 fun <T: Any> T.logger() = LoggerFactory.getLogger(this::class.java)

src/main/java/icu/samnyan/aqua/net/games/mai2/Maimai2.kt

@@ -175,10 +175,12 @@ class Maimai2(
         SUCCESS
     }
 
+    val photoDir = UploadUserPhotoHandler.uploadDir.toFile().canonicalFile
+
     @API("my-photo")
     suspend fun myPhoto(@RP token: Str) = us.jwt.auth(token) { u ->
         val find = "${u.ghostCard.extId}-"
-        UploadUserPhotoHandler.uploadDir.toFile().listFiles()
+        photoDir.listFiles()
             ?.map { it.name }
             ?.filter { it.startsWith(find) }
             ?.sorted()
@@ -187,8 +189,9 @@ class Maimai2(
 
     @API("my-photo/{fileName}", produces = [MediaType.IMAGE_JPEG_VALUE])
     suspend fun myPhoto(@RP token: Str, @PV fileName: Str) = us.jwt.auth(token) { u ->
-        if (!fileName.startsWith("${u.ghostCard.extId}-")) (403 - "Not your photo")
-        val f = (UploadUserPhotoHandler.uploadDir / fileName).toFile()
+        val f = (photoDir / fileName)
+        if (!f.canonicalFile.startsWith(photoDir)) (403 - "Never gonna give you up")
+        if (!f.name.startsWith("${u.ghostCard.extId}-")) (403 - "Not your photo")
         if (!f.exists()) (404 - "Photo not found")
         f.readBytes()
     }