fix: stop exporting DecryptActivity and validate decrypt paths

DecryptActivity was exported without an intent filter, so any installed
app could start it with arbitrary FILE_PATH/REPO_PATH extras (and crash
it by omitting them). Nothing outside the app needs to launch it:
shortcuts and the decrypt action go through LaunchActivity.

LaunchActivity stays exported, so it now treats FILE_PATH as untrusted:
the path is forwarded only when it canonically resolves to a regular
file inside the password store, and REPO_PATH is always the real store
directory instead of the caller-supplied value. Anything else falls
back to the main screen.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/app/src/test/java/app/passwordstore/ui/main/LaunchActivityTest.kt b/app/src/test/java/app/passwordstore/ui/main/LaunchActivityTest.kt
new file mode 100644
index 00000000..3c30071a
--- /dev/null
+++ b/app/src/test/java/app/passwordstore/ui/main/LaunchActivityTest.kt
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+package app.passwordstore.ui.main
+
+import app.passwordstore.ui.main.LaunchActivity.Companion.isFileInRepo
+import java.io.File
+import java.nio.file.Files
+import kotlin.test.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class LaunchActivityTest {
+
+  @Test
+  fun onlyAcceptsFilesInsideTheRepository() {
+    val root = Files.createTempDirectory("aps").toFile()
+    val repo = File(root, "store").apply { mkdirs() }
+    val inside =
+      File(repo, "site/login.gpg").apply {
+        parentFile!!.mkdirs()
+        writeText("x")
+      }
+    val outside = File(root, "secret.gpg").apply { writeText("x") }
+    val sibling =
+      File(root, "store-evil/login.gpg").apply {
+        parentFile!!.mkdirs()
+        writeText("x")
+      }
+    val link = File(repo, "link.gpg").toPath()
+    Files.createSymbolicLink(link, outside.toPath())
+
+    assertTrue(isFileInRepo(inside.absolutePath, repo))
+    assertFalse(isFileInRepo(outside.absolutePath, repo))
+    assertFalse(isFileInRepo("${repo.absolutePath}/../secret.gpg", repo))
+    assertFalse(isFileInRepo(sibling.absolutePath, repo))
+    assertFalse(isFileInRepo(link.toString(), repo))
+    assertFalse(isFileInRepo(repo.absolutePath, repo))
+    assertFalse(isFileInRepo(File(repo, "missing.gpg").absolutePath, repo))
+    assertFalse(isFileInRepo(null, repo))
+    assertFalse(isFileInRepo("", repo))
+    root.deleteRecursively()
+  }
+}