Issue #18763: subprocess: The file descriptors are now closed after calling the

preexec_fn callback, which may open file descriptors.

1 files changed, 12 insertions, 11 deletions

diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index 07d7096..8d65530 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -412,17 +412,6 @@ child_exec(char *const exec_array[],
         POSIX_CALL(close(errwrite));
     }
 
-    if (close_fds) {
-        int local_max_fd = max_fd;
-#if defined(__NetBSD__)
-        local_max_fd = fcntl(0, F_MAXFD);
-        if (local_max_fd < 0)
-            local_max_fd = max_fd;
-#endif
-        /* TODO HP-UX could use pstat_getproc() if anyone cares about it. */
-        _close_open_fd_range(3, local_max_fd, py_fds_to_keep);
-    }
-
     if (cwd)
         POSIX_CALL(chdir(cwd));
 
@@ -451,6 +440,18 @@ child_exec(char *const exec_array[],
         /* Py_DECREF(result); - We're about to exec so why bother? */
     }
 
+    /* close FDs after executing preexec_fn, which might open FDs */
+    if (close_fds) {
+        int local_max_fd = max_fd;
+#if defined(__NetBSD__)
+        local_max_fd = fcntl(0, F_MAXFD);
+        if (local_max_fd < 0)
+            local_max_fd = max_fd;
+#endif
+        /* TODO HP-UX could use pstat_getproc() if anyone cares about it. */
+        _close_open_fd_range(3, local_max_fd, py_fds_to_keep);
+    }
+
     /* This loop matches the Lib/os.py _execvpe()'s PATH search when */
     /* given the executable_list generated by Lib/subprocess.py.     */
     saved_errno = 0;