From d7f37f6455a08ac164efbddf381fac2b08d6c16c Mon Sep 17 00:00:00 2001
From: Reagan Bohan <xbjfk.github@gmail.com>
Date: Mon, 21 Apr 2025 08:44:43 +0000
Subject: [PATCH] Fix mmap aborting with invalid fd in debug mode

---
 stdlib/src/mmap.rs | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/stdlib/src/mmap.rs b/stdlib/src/mmap.rs
index bca367ae4d..9319bab64c 100644
--- a/stdlib/src/mmap.rs
+++ b/stdlib/src/mmap.rs
@@ -23,13 +23,15 @@ mod mmap {
     };
     use crossbeam_utils::atomic::AtomicCell;
     use memmap2::{Advice, Mmap, MmapMut, MmapOptions};
+    #[cfg(unix)]
+    use nix::sys::stat::fstat;
     use nix::unistd;
     use num_traits::Signed;
     use std::fs::File;
-    use std::io::Write;
+    use std::io::{self, Write};
     use std::ops::{Deref, DerefMut};
     #[cfg(unix)]
-    use std::os::unix::io::{FromRawFd, IntoRawFd, RawFd};
+    use std::os::unix::io::{FromRawFd, RawFd};
 
     fn advice_try_from_i32(vm: &VirtualMachine, i: i32) -> PyResult<Advice> {
         Ok(match i {
@@ -299,7 +301,7 @@ mod mmap {
         fn py_new(
             cls: PyTypeRef,
             MmapNewArgs {
-                fileno: mut fd,
+                fileno: fd,
                 length,
                 flags,
                 prot,
@@ -348,12 +350,10 @@ mod mmap {
             };
 
             if fd != -1 {
-                let file = unsafe { File::from_raw_fd(fd) };
-                let metadata = file.metadata().map_err(|err| err.to_pyexception(vm))?;
-                let file_len: libc::off_t = metadata.len().try_into().expect("file size overflow");
-                // File::from_raw_fd will consume the fd, so we
-                // have to  get it again.
-                fd = file.into_raw_fd();
+                let metadata = fstat(fd)
+                    .map_err(|err| io::Error::from_raw_os_error(err as i32).to_pyexception(vm))?;
+                let file_len = metadata.st_size;
+
                 if map_size == 0 {
                     if file_len == 0 {
                         return Err(vm.new_value_error("cannot mmap an empty file".to_owned()));