From eea3a6084930f965d9e4e583d80f55bb064fd01c Mon Sep 17 00:00:00 2001
From: Hood Chatham <roberthoodchatham@gmail.com>
Date: Sat, 19 Jul 2025 18:43:39 +0200
Subject: [PATCH] gh-124621: Emscripten: Fix regression in use-after-close
 error handling

Introduced in GH-136822. If the fd is already closed,
`SYSCALLS.getStreamFromFD()` throws an error. We need to catch it and
discard it. The `__wasi_fd_read_orig()` fallback will use it to set errno.
---
 Python/emscripten_syscalls.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/Python/emscripten_syscalls.c b/Python/emscripten_syscalls.c
index bd5cc07071f20e..886262acbc6810 100644
--- a/Python/emscripten_syscalls.c
+++ b/Python/emscripten_syscalls.c
@@ -148,10 +148,17 @@ EM_JS_MACROS(__externref_t, __maybe_fd_read_async, (
     size_t iovcnt,
     __wasi_size_t *nread
 ), {
-    var stream = SYSCALLS.getStreamFromFD(fd);
     if (!WebAssembly.promising) {
         return null;
     }
+    var stream;
+    try {
+        stream = SYSCALLS.getStreamFromFD(fd);
+    } catch (e) {
+        // If the fd was already closed or never existed, getStreamFromFD()
+        // raises. We'll let fd_read_orig() handle setting errno.
+        return null;
+    }
     if (!stream.stream_ops.readAsync) {
         // Not an async device. Fall back to __wasi_fd_read_orig().
         return null;