fix(cli): harden permission stdio check (#21778)

Harden the code that does permission checks to protect against
re-opening of stdin.

Code that runs FFI is vulnerable to an attack where fd 0 is closed
during a permission check and re-opened with a file that contains a
positive response (ie: `y` or `A`). While FFI code is dangerous in
general, we can make it more difficult for FFI-enabled code to bypass
additional permission checks.

- Checks to see if the underlying file for stdin has changed from the
start to the end of the permission check (detects races)
- Checks to see if the message is excessively long (lowering the window
for races)
- Checks to see if stdin and stderr are still terminals at the end of
the function (making races more difficult)

2 files changed, 15 insertions, 0 deletions

diff --git a/cli/tests/integration/run_tests.rs b/cli/tests/integration/run_tests.rs
index 43bc212c6..36eee1100 100644
--- a/cli/tests/integration/run_tests.rs
+++ b/cli/tests/integration/run_tests.rs
@@ -707,6 +707,20 @@ fn permissions_prompt_allow_all_lowercase_a() {
     });
 }
 
+#[test]
+fn permission_request_long() {
+  TestContext::default()
+    .new_command()
+    .args_vec(["run", "--quiet", "run/permission_request_long.ts"])
+    .with_pty(|mut console| {
+      console.expect(concat!(
+        "❌ Permission prompt length (100017 bytes) was larger than the configured maximum length (10240 bytes): denying request.\r\n",
+        "❌ WARNING: This may indicate that code is trying to bypass or hide permission check requests.\r\n",
+        "❌ Run again with --allow-read to bypass this check if this is really what you want to do.\r\n",
+      ));
+    });
+}
+
 itest!(deny_all_permission_args {
   args: "run --deny-env --deny-read --deny-write --deny-ffi --deny-run --deny-sys --deny-net --deny-hrtime run/deny_all_permission_args.js",
   output: "run/deny_all_permission_args.out",
diff --git a/cli/tests/testdata/run/permission_request_long.ts b/cli/tests/testdata/run/permission_request_long.ts
new file mode 100644
index 000000000..05937e95a
--- /dev/null
+++ b/cli/tests/testdata/run/permission_request_long.ts
@@ -0,0 +1 @@
+Deno.open("a".repeat(1e5));